手写Spring框架-笔记

参考文章：
https://github.com/DerekYRC/mini-spring
https://juejin.cn/post/6989013058035122207#heading-14

后者也是借鉴的前者哦。

当我们自己想实现一个Spring框架的时候，想想我们需要实现哪些功能。

版本V1.0 实现一个简单的Bean容器

 

先从最基础的部分开始，实现bean的定义、注册、获取。我们首先需要一个容器，我们可以通过这个容器获取bean。那容器里的bean是从哪来的呢？然后我们再考虑需要将bean注册到容器里面。
定义BeanFactoy作为容器，定义BeanDefinition作为bean的注册类。具体实现如下

public class BeanFactory {
    private Map<String, BeanDefinition> beanDefinitionMap = new ConcurrentHashMap<>();

    public void registerBeanDefinition(String name, BeanDefinition obj) {
        beanDefinitionMap.put(name, obj);
    }

    public Object getBean(String name) {
        return beanDefinitionMap.get(name).getBean();
    }
}

public class BeanDefinition {

    private Object bean;

    public BeanDefinition(Object bean) {
        this.bean = bean;
    }


    public Object getBean() {
        return bean;
    }
}

测试代码如下：

public class ApiTest {

    @Test
    public void test_BeanFactory(){
        // 1.初始化 BeanFactory
        BeanFactory beanFactory = new BeanFactory();

        // 2.注入bean
        BeanDefinition beanDefinition = new BeanDefinition(new Object());
        beanFactory.registerBeanDefinition("test", beanDefinition);

        // 3.获取bean
        Object userService = beanFactory.getBean("test");
        userService.toString();
    }

}

 这样我们就获得了一个最基本的框架版本V1.0

 

版本V2.0 运用设计模式，实现 Bean 的定义、注册、获取

 

 

 

对BeanFactory进行更细致化的划分，更迭结果如下。

代码

public class BeanDefinition {

    private Class beanClass;

    public BeanDefinition(Class beanClass) {
        this.beanClass = beanClass;
    }

    public Class getBeanClass() {
        return beanClass;
    }

    public void setBeanClass(Class beanClass) {
        this.beanClass = beanClass;
    }
}

public class DefaultSingletonBeanRegistry implements SingletonBeanRegistry {
    private final Map<String, Object> singletonObjects = new HashMap<>();

    @Override
    public Object getSingleton(String beanName) {
        return singletonObjects.get(beanName);
    }

    protected void addSingleton(String beanName, Object singletonObject) {
        singletonObjects.put(beanName, singletonObject);
    }
}

public abstract class AbstractBeanFactory extends DefaultSingletonBeanRegistry implements BeanFactory {
    @Override
    public Object getBean(String beanName) throws BeanException {
        Object bean = getSingleton(beanName);
        if (bean != null) {
            System.out.println("exist bean " + beanName);
            return bean;
        }
        BeanDefinition beanDefinition = getBeanDefinition(beanName);
        return createBean(beanName, beanDefinition);

    }

    protected abstract BeanDefinition getBeanDefinition(String beanName);

    protected abstract Object createBean(String beanName, BeanDefinition beanDefinition);
}

public abstract class AbstractAutowireCapableBean extends AbstractBeanFactory{

    @Override
    protected Object createBean(String beanName, BeanDefinition beanDefinition) throws BeansException {
        Object bean;
        try {
            bean = beanDefinition.getBeanClass().newInstance();
        } catch (InstantiationException | IllegalAccessException e) {
            throw new BeansException("Instantiation of bean failed", e);
        }

        addSingleton(beanName, bean);
        return bean;
    }
}

public class DefaultListableBeanFactory  extends AbstractAutowireCapableBean implements BeanDefinitionRegistry {
    private final Map<String, BeanDefinition> beanDefinitionMap = new HashMap<>();

    @Override
    public void registerBeanDefinition(String beanName, BeanDefinition beanDefinition) {
        beanDefinitionMap.put(beanName, beanDefinition);
    }

    @Override
    public BeanDefinition getBeanDefinition(String beanName) throws BeansException {
        BeanDefinition beanDefinition = beanDefinitionMap.get(beanName);
        if (beanDefinition == null) throw new BeansException("No bean named '" + beanName + "' is defined");
        return beanDefinition;
    }
}

 测试代码

public class ApiTest {

    @Test
    public void test_BeanFactory(){
        // 1.初始化 BeanFactory
        DefaultListableBeanFactory beanFactory = new DefaultListableBeanFactory();

        // 2.注册 bean
        BeanDefinition beanDefinition = new BeanDefinition(UserService.class);
        beanFactory.registerBeanDefinition("userService", beanDefinition);

        // 3.第一次获取 bean
        UserService userService = (UserService) beanFactory.getBean("userService");
        userService.queryUserInfo();

        // 4.第二次获取 bean from Singleton
        UserService userService_singleton = (UserService) beanFactory.getSingleton("userService");
        userService_singleton.queryUserInfo();
    }

}

 

 

 

版本V3.0 基于Cglib实现含构造函数的类实例化策略

 

 

 

对bean的实例化进行迭代，实现带参数的bean的实例化 

 BeanFactory增加带参数的getBean()方法，在实例化的时候根据配置的策略决定使用哪种方法。

public interface BeanFactory {
    Object getBean(String name) throws BeanException;

    Object getBean(String name, Object ...args) throws BeanException;
}

public abstract class AbstractBeanFactory extends DefaultSingletonBeanRegistry implements BeanFactory {
    @Override
    public Object getBean(String name) throws BeansException {
        return doGetBean(name, null);
    }

    @Override
    public Object getBean(String name, Object... args) throws BeansException {
        return doGetBean(name, args);
    }

    protected <T> T doGetBean(final String name, final Object[] args) {
        Object bean = getSingleton(name);
        if (bean != null) {
            return (T) bean;
        }

        BeanDefinition beanDefinition = getBeanDefinition(name);
        return (T) createBean(name, beanDefinition, args);
    }

    protected abstract BeanDefinition getBeanDefinition(String beanName) throws BeansException;

    protected abstract Object createBean(String beanName, BeanDefinition beanDefinition, Object[] args) throws BeansException;
}

public abstract class AbstractAutowireCapableBean extends AbstractBeanFactory{


    private InstantiationStrategy instantiationStrategy = new CglibSubclassingInstantiationStrategy();

    @Override
    protected Object createBean(String beanName, BeanDefinition beanDefinition, Object[] args) throws BeansException {
        Object bean = null;
        try {
            bean = createBeanInstance(beanDefinition, beanName, args);
        } catch (Exception e) {
            throw new BeansException("Instantiation of bean failed", e);
        }

        addSingleton(beanName, bean);
        return bean;
    }

    protected Object createBeanInstance(BeanDefinition beanDefinition, String beanName, Object[] args) {
        Constructor constructorToUse = null;
        Class<?> beanClass = beanDefinition.getBeanClass();
        Constructor<?>[] declaredConstructors = beanClass.getDeclaredConstructors();
        for (Constructor ctor : declaredConstructors) {
            if (null != args && ctor.getParameterTypes().length == args.length) {
                constructorToUse = ctor;
                break;
            }
        }
        return getInstantiationStrategy().instantiate(beanDefinition, beanName, constructorToUse, args);
    }

    public InstantiationStrategy getInstantiationStrategy() {
        return instantiationStrategy;
    }

    public void setInstantiationStrategy(InstantiationStrategy instantiationStrategy) {
        this.instantiationStrategy = instantiationStrategy;
    }
}

public class CglibSubclassingInstantiationStrategy implements InstantiationStrategy {

    @Override
    public Object instantiate(BeanDefinition beanDefinition, String beanName, Constructor ctor, Object[] args) throws BeansException {
        Enhancer enhancer = new Enhancer();
        enhancer.setSuperclass(beanDefinition.getBeanClass());
        enhancer.setCallback(new NoOp() {
            @Override
            public int hashCode() {
                return super.hashCode();
            }
        });
        if (null == ctor) return enhancer.create();
        return enhancer.create(ctor.getParameterTypes(), args);
    }

}

public class SimpleInstantiationStrategy implements InstantiationStrategy {

    @Override
    public Object instantiate(BeanDefinition beanDefinition, String beanName, Constructor ctor, Object[] args) throws BeansException {
        Class clazz = beanDefinition.getBeanClass();
        try {
            if (null != ctor) {
                return clazz.getDeclaredConstructor(ctor.getParameterTypes()).newInstance(args);
            } else {
                return clazz.getDeclaredConstructor().newInstance();
            }
        } catch (NoSuchMethodException | InstantiationException | IllegalAccessException | InvocationTargetException e) {
            throw new BeansException("Failed to instantiate [" + clazz.getName() + "]", e);
        }
    }

}

测试代码

    public void test_BeanFactory() {
        // 1.初始化 BeanFactory
        DefaultListableBeanFactory beanFactory = new DefaultListableBeanFactory();

        // 2.注入bean
        BeanDefinition beanDefinition = new BeanDefinition(new UserService().getClass());
        beanFactory.registerBeanDefinition("userService", beanDefinition);

        // 3.获取bean
        UserService userService = (UserService) beanFactory.getBean("userService","name");
        userService.queryUserInfo();
        
    }

 

版本V4.0 为Bean对象注入属性和依赖Bean的功能实现

 

 

 

对BeanDefinition进行优化，增加propertyValue。填充bean的属性值（包含bean类型的属性值）

public class BeanDefinition {

    private Class beanClass;

    private PropertyValues propertyValues;

    public BeanDefinition(Class beanClass) {
        this.beanClass = beanClass;
        this.propertyValues = new PropertyValues();
    }

    public BeanDefinition(Class beanClass, PropertyValues propertyValues) {
        this.beanClass = beanClass;
        this.propertyValues = propertyValues;
    }

    public Class getBeanClass() {
        return beanClass;
    }

    public void setBeanClass(Class beanClass) {
        this.beanClass = beanClass;
    }

    public PropertyValues getPropertyValues() {
        return propertyValues;
    }

    public void setPropertyValues(PropertyValues propertyValues) {
        this.propertyValues = propertyValues;
    }
}

public class PropertyValues {

    private final List<PropertyValue> propertyValueList = new ArrayList<>();

    public void addPropertyValue(PropertyValue pv) {
        this.propertyValueList.add(pv);
    }

    public PropertyValue[] getPropertyValues() {
        return this.propertyValueList.toArray(new PropertyValue[0]);
    }

    public PropertyValue getPropertyValue(String propertyName) {
        for (PropertyValue pv : this.propertyValueList) {
            if (pv.getName().equals(propertyName)) {
                return pv;
            }
        }
        return null;
    }

}

public class PropertyValue {

    private final String name;

    private final Object value;

    public PropertyValue(String name, Object value) {
        this.name = name;
        this.value = value;
    }

    public String getName() {
        return name;
    }

    public Object getValue() {
        return value;
    }

}

public abstract class AbstractAutowireCapableBean extends AbstractBeanFactory{


    private InstantiationStrategy instantiationStrategy = new CglibSubclassingInstantiationStrategy();

    @Override
    protected Object createBean(String beanName, BeanDefinition beanDefinition, Object[] args) throws BeansException {
        Object bean = null;
        try {
            bean = createBeanInstance(beanDefinition, beanName, args);
            // 给 Bean 填充属性
            applyPropertyValues(beanName, bean, beanDefinition);
        } catch (Exception e) {
            throw new BeansException("Instantiation of bean failed", e);
        }

        addSingleton(beanName, bean);
        return bean;
    }

    /**
     * Bean 属性填充
     */
    protected void applyPropertyValues(String beanName, Object bean, BeanDefinition beanDefinition) {
        try {
            PropertyValues propertyValues = beanDefinition.getPropertyValues();
            for (PropertyValue propertyValue : propertyValues.getPropertyValues()) {

                String name = propertyValue.getName();
                Object value = propertyValue.getValue();

                if (value instanceof BeanReference) {
                    // A 依赖 B，获取 B 的实例化
                    BeanReference beanReference = (BeanReference) value;
                    value = getBean(beanReference.getBeanName());
                }
                // 属性填充
                BeanUtil.setFieldValue(bean, name, value);
            }
        } catch (Exception e) {
            throw new BeansException("Error setting property values：" + beanName);
        }
    }

    protected Object createBeanInstance(BeanDefinition beanDefinition, String beanName, Object[] args) {
        Constructor constructorToUse = null;
        Class<?> beanClass = beanDefinition.getBeanClass();
        Constructor<?>[] declaredConstructors = beanClass.getDeclaredConstructors();
        for (Constructor ctor : declaredConstructors) {
            if (null != args && ctor.getParameterTypes().length == args.length) {
                constructorToUse = ctor;
                break;
            }
        }
        return getInstantiationStrategy().instantiate(beanDefinition, beanName, constructorToUse, args);
    }

    public InstantiationStrategy getInstantiationStrategy() {
        return instantiationStrategy;
    }

    public void setInstantiationStrategy(InstantiationStrategy instantiationStrategy) {
        this.instantiationStrategy = instantiationStrategy;
    }
}

测试代码

@Test
    public void test_BeanFactory() {
        // 1.初始化 BeanFactory
        DefaultListableBeanFactory beanFactory = new DefaultListableBeanFactory();

        // 2. UserDao 注册
        beanFactory.registerBeanDefinition("userDao", new BeanDefinition(UserDao.class));

        // 3. UserService 设置属性[uId、userDao]
        PropertyValues propertyValues = new PropertyValues();
        propertyValues.addPropertyValue(new PropertyValue("uId", "10001"));
        propertyValues.addPropertyValue(new PropertyValue("userDao",new BeanReference("userDao")));

        // 4. UserService 注入bean
        BeanDefinition beanDefinition = new BeanDefinition(UserService.class, propertyValues);
        beanFactory.registerBeanDefinition("userService", beanDefinition);

        // 5. UserService 获取bean
        UserService userService = (UserService) beanFactory.getBean("userService");
        userService.queryUserInfo();
    }

版本V5.0 设计与实现资源加载器，从Spring.xml解析和注册Bean对象

增加xml文件解析功能，从spring.xml解析跟注册bean
在XmlBeanDefinitionReader中进行xml文件解析，将解析出的beanDefinition 注册到BeanFactory中。

public abstract class AbstractBeanDefinitionReader implements BeanDefinitionReader {

    private final BeanDefinitionRegistry registry;

    private ResourceLoader resourceLoader;

    protected AbstractBeanDefinitionReader(BeanDefinitionRegistry registry) {
        this(registry, new DefaultResourceLoader());
    }

    public AbstractBeanDefinitionReader(BeanDefinitionRegistry registry, ResourceLoader resourceLoader) {
        this.registry = registry;
        this.resourceLoader = resourceLoader;
    }

    @Override
    public BeanDefinitionRegistry getRegistry() {
        return registry;
    }

    @Override
    public ResourceLoader getResourceLoader() {
        return resourceLoader;
    }

}

public class XmlBeanDefinitionReader extends AbstractBeanDefinitionReader {

    public XmlBeanDefinitionReader(BeanDefinitionRegistry registry) {
        super(registry);
    }

    public XmlBeanDefinitionReader(BeanDefinitionRegistry registry, ResourceLoader resourceLoader) {
        super(registry, resourceLoader);
    }

    @Override
    public void loadBeanDefinitions(Resource resource) throws BeansException {
        try {
            try (InputStream inputStream = resource.getInputStream()) {
                doLoadBeanDefinitions(inputStream);
            }
        } catch (IOException | ClassNotFoundException e) {
            throw new BeansException("IOException parsing XML document from " + resource, e);
        }
    }

    @Override
    public void loadBeanDefinitions(Resource... resources) throws BeansException {
        for (Resource resource : resources) {
            loadBeanDefinitions(resource);
        }
    }

    @Override
    public void loadBeanDefinitions(String location) throws BeansException {
        ResourceLoader resourceLoader = getResourceLoader();
        Resource resource = resourceLoader.getResource(location);
        loadBeanDefinitions(resource);
    }

    protected void doLoadBeanDefinitions(InputStream inputStream) throws ClassNotFoundException {
        Document doc = XmlUtil.readXML(inputStream);
        Element root = doc.getDocumentElement();
        NodeList childNodes = root.getChildNodes();

        for (int i = 0; i < childNodes.getLength(); i++) {
            // 判断元素
            if (!(childNodes.item(i) instanceof Element)) continue;
            // 判断对象
            if (!"bean".equals(childNodes.item(i).getNodeName())) continue;
            
            // 解析标签
            Element bean = (Element) childNodes.item(i);
            String id = bean.getAttribute("id");
            String name = bean.getAttribute("name");
            String className = bean.getAttribute("class");
            // 获取 Class，方便获取类中的名称
            Class<?> clazz = Class.forName(className);
            // 优先级 id > name
            String beanName = StrUtil.isNotEmpty(id) ? id : name;
            if (StrUtil.isEmpty(beanName)) {
                beanName = StrUtil.lowerFirst(clazz.getSimpleName());
            }

            // 定义Bean
            BeanDefinition beanDefinition = new BeanDefinition(clazz);
            // 读取属性并填充
            for (int j = 0; j < bean.getChildNodes().getLength(); j++) {
                if (!(bean.getChildNodes().item(j) instanceof Element)) continue;
                if (!"property".equals(bean.getChildNodes().item(j).getNodeName())) continue;
                // 解析标签：property
                Element property = (Element) bean.getChildNodes().item(j);
                String attrName = property.getAttribute("name");
                String attrValue = property.getAttribute("value");
                String attrRef = property.getAttribute("ref");
                // 获取属性值：引入对象、值对象
                Object value = StrUtil.isNotEmpty(attrRef) ? new BeanReference(attrRef) : attrValue;
                // 创建属性信息
                PropertyValue propertyValue = new PropertyValue(attrName, value);
                beanDefinition.getPropertyValues().addPropertyValue(propertyValue);
            }
            if (getRegistry().containsBeanDefinition(beanName)) {
                throw new BeansException("Duplicate beanName[" + beanName + "] is not allowed");
            }
            // 注册 BeanDefinition
            getRegistry().registerBeanDefinition(beanName, beanDefinition);
        }
    }

}

测试代码

public class UserDao {

    private static Map<String, String> hashMap = new HashMap<>();

    static {
        hashMap.put("1", "a");
        hashMap.put("2", "b");
        hashMap.put("3", "c");
    }

    public String queryUserName(String uId) {
        return hashMap.get(uId);
    }

}

public class UserService {

    private String uId;

    private UserDao userDao;

    public String queryUserInfo() {
        return ("查询用户信息：" + userDao.queryUserName(uId));
    }

    public String getuId() {
        return uId;
    }

    public void setuId(String uId) {
        this.uId = uId;
    }

    public UserDao getUserDao() {
        return userDao;
    }

    public void setUserDao(UserDao userDao) {
        this.userDao = userDao;
    }
}


    public void test_BeanFactory() {
        // 1.初始化 BeanFactory
        DefaultListableBeanFactory beanFactory = new DefaultListableBeanFactory();

        // 2. 读取配置文件&注册Bean
        XmlBeanDefinitionReader reader = new XmlBeanDefinitionReader(beanFactory);
        reader.loadBeanDefinitions("classpath:spring.xml");

        // 3. 获取Bean对象调用方法
        UserService userService = beanFactory.getBean("userService", UserService.class);
        String result = userService.queryUserInfo();
        System.out.println("测试结果：" + result);
    }

测试xml

<?xml version="1.0" encoding="UTF-8"?>
<beans>

    <bean id="userDao" class="springframework.UserDao"/>

    <bean id="userService" class="springframework.UserService">
        <property name="uId" value="1"/>
        <property name="userDao" ref="userDao"/>
    </bean>

</beans>

 

版本V6.0 实现应用上下文，自动识别、资源加载、扩展机制。向虚拟机注册钩子，实现Bean对象的初始化和销毁方法

 

 

 

实现BeanFactoryPostProcess 和 BeanPostProcessor接口。

BeanFactoryPostProcess：SpringIOC容器允许BeanFactoryPostProcessor在容器实际实例化任何bean之前读取beanDefinition,并有可能修改他.并且我们还可以配置自定义的BeanFactoryPostProcessor.如果想改变bean,那么使用beanPostProcessor。

BeanPostProcessor：作用是在Bean对象在实例化和依赖注入完毕后，在显示调用初始化方法的前后添加我们自己的逻辑。

 

BeanFactoryPostProcess主要实现逻辑是在 beanDefinition生成后进行修改。

BeanPostProcessor 生效阶段是在bean 实例化、填充属性后，执行接口。

 

AbstractApplicationContext完成的任务：生成beanFactory、根据BeanFactoryPostProcess修改beanDefinition、注册实例化BeanPostProcessor对象

在AbstractAutowireCapableBean中处理init、BeanPostProcessor方法

public interface BeanFactoryPostProcessor {

    /**
     * 在所有的 BeanDefinition 加载完成后，实例化 Bean 对象之前，提供修改 BeanDefinition 属性的机制
     *
     */
    void postProcessBeanFactory(ConfigurableListableBeanFactory beanFactory) throws BeansException;

}

public interface BeanPostProcessor {

    /**
     * 在 Bean 对象执行初始化方法之前，执行此方法
     *
     * @param bean
     * @param beanName
     * @return
     * @throws BeansException
     */
    Object postProcessBeforeInitialization(Object bean, String beanName) throws BeansException;

    /**
     * 在 Bean 对象执行初始化方法之后，执行此方法
     *
     * @param bean
     * @param beanName
     * @return
     * @throws BeansException
     */
    Object postProcessAfterInitialization(Object bean, String beanName) throws BeansException;

}

public abstract class AbstractAutowireCapableBean extends AbstractBeanFactory implements AutowireCapableBeanFactory {


    private InstantiationStrategy instantiationStrategy = new CglibSubclassingInstantiationStrategy();

    @Override
    protected Object createBean(String beanName, BeanDefinition beanDefinition, Object[] args) throws BeansException {
        Object bean = null;
        try {
            bean = createBeanInstance(beanDefinition, beanName, args);
            // 给 Bean 填充属性
            applyPropertyValues(beanName, bean, beanDefinition);

            // 执行 Bean 的初始化方法和 BeanPostProcessor 的前置和后置处理方法
            bean = initializeBean(beanName, bean, beanDefinition);
        } catch (Exception e) {
            throw new BeansException("Instantiation of bean failed", e);
        }

        addSingleton(beanName, bean);
        return bean;
    }

    /**
     * Bean 属性填充
     */
    protected void applyPropertyValues(String beanName, Object bean, BeanDefinition beanDefinition) {
        try {
            PropertyValues propertyValues = beanDefinition.getPropertyValues();
            for (PropertyValue propertyValue : propertyValues.getPropertyValues()) {

                String name = propertyValue.getName();
                Object value = propertyValue.getValue();

                if (value instanceof BeanReference) {
                    // A 依赖 B，获取 B 的实例化
                    BeanReference beanReference = (BeanReference) value;
                    value = getBean(beanReference.getBeanName());
                }
                // 属性填充
                BeanUtil.setFieldValue(bean, name, value);
            }
        } catch (Exception e) {
            throw new BeansException("Error setting property values：" + beanName);
        }
    }

    protected Object createBeanInstance(BeanDefinition beanDefinition, String beanName, Object[] args) {
        Constructor constructorToUse = null;
        Class<?> beanClass = beanDefinition.getBeanClass();
        Constructor<?>[] declaredConstructors = beanClass.getDeclaredConstructors();
        for (Constructor ctor : declaredConstructors) {
            if (null != args && ctor.getParameterTypes().length == args.length) {
                constructorToUse = ctor;
                break;
            }
        }
        return getInstantiationStrategy().instantiate(beanDefinition, beanName, constructorToUse, args);
    }

    public InstantiationStrategy getInstantiationStrategy() {
        return instantiationStrategy;
    }

    public void setInstantiationStrategy(InstantiationStrategy instantiationStrategy) {
        this.instantiationStrategy = instantiationStrategy;
    }

    private Object initializeBean(String beanName, Object bean, BeanDefinition beanDefinition) {
        // 1. 执行 BeanPostProcessor Before 处理
        Object wrappedBean = applyBeanPostProcessorsBeforeInitialization(bean, beanName);

        // 待完成内容：invokeInitMethods(beanName, wrappedBean, beanDefinition);
        invokeInitMethods(beanName, wrappedBean, beanDefinition);

        // 2. 执行 BeanPostProcessor After 处理
        wrappedBean = applyBeanPostProcessorsAfterInitialization(wrappedBean, beanName);
        return wrappedBean;
    }

    private void invokeInitMethods(String beanName, Object wrappedBean, BeanDefinition beanDefinition) {

    }

    @Override
    public Object applyBeanPostProcessorsBeforeInitialization(Object existingBean, String beanName) throws BeansException {
        Object result = existingBean;
        for (BeanPostProcessor processor : getBeanPostProcessors()) {
            Object current = processor.postProcessBeforeInitialization(result, beanName);
            if (null == current) return result;
            result = current;
        }
        return result;
    }

    @Override
    public Object applyBeanPostProcessorsAfterInitialization(Object existingBean, String beanName) throws BeansException {
        Object result = existingBean;
        for (BeanPostProcessor processor : getBeanPostProcessors()) {
            Object current = processor.postProcessAfterInitialization(result, beanName);
            if (null == current) return result;
            result = current;
        }
        return result;
    }
}

public abstract class AbstractApplicationContext extends DefaultResourceLoader implements ConfigurableApplicationContext {

    @Override
    public void refresh() throws BeansException {
        // 1. 创建 BeanFactory，并加载 BeanDefinition
        refreshBeanFactory();

        // 2. 获取 BeanFactory
        ConfigurableListableBeanFactory beanFactory = getBeanFactory();

        // 3. 在 Bean 实例化之前，执行 BeanFactoryPostProcessor (Invoke factory processors registered as beans in the context.)
        invokeBeanFactoryPostProcessors(beanFactory);

        // 4. BeanPostProcessor 需要提前于其他 Bean 对象实例化之前执行注册操作
        registerBeanPostProcessors(beanFactory);

        // 5. 提前实例化单例Bean对象
        beanFactory.preInstantiateSingletons();
    }

    protected abstract void refreshBeanFactory() throws BeansException;

    protected abstract ConfigurableListableBeanFactory getBeanFactory();

    private void invokeBeanFactoryPostProcessors(ConfigurableListableBeanFactory beanFactory) {
        Map<String, BeanFactoryPostProcessor> beanFactoryPostProcessorMap = beanFactory.getBeansOfType(BeanFactoryPostProcessor.class);
        for (BeanFactoryPostProcessor beanFactoryPostProcessor : beanFactoryPostProcessorMap.values()) {
            beanFactoryPostProcessor.postProcessBeanFactory(beanFactory);
        }
    }

    private void registerBeanPostProcessors(ConfigurableListableBeanFactory beanFactory) {
        Map<String, BeanPostProcessor> beanPostProcessorMap = beanFactory.getBeansOfType(BeanPostProcessor.class);
        for (BeanPostProcessor beanPostProcessor : beanPostProcessorMap.values()) {
            beanFactory.addBeanPostProcessor(beanPostProcessor);
        }
    }

    @Override
    public <T> Map<String, T> getBeansOfType(Class<T> type) throws BeansException {
        return getBeanFactory().getBeansOfType(type);
    }

    @Override
    public String[] getBeanDefinitionNames() {
        return getBeanFactory().getBeanDefinitionNames();
    }

    @Override
    public Object getBean(String name) throws BeansException {
        return getBeanFactory().getBean(name);
    }

    @Override
    public Object getBean(String name, Object... args) throws BeansException {
        return getBeanFactory().getBean(name, args);
    }

    @Override
    public <T> T getBean(String name, Class<T> requiredType) throws BeansException {
        return getBeanFactory().getBean(name, requiredType);
    }

    @Override
    public void registerShutdownHook() {
        Runtime.getRuntime().addShutdownHook(new Thread(this::close));
    }

    @Override
    public void close() {
        getBeanFactory().destroySingletons();
    }

}

public abstract class AbstractAutowireCapableBean extends AbstractBeanFactory implements AutowireCapableBeanFactory {


    private InstantiationStrategy instantiationStrategy = new CglibSubclassingInstantiationStrategy();

    @Override
    protected Object createBean(String beanName, BeanDefinition beanDefinition, Object[] args) throws BeansException {
        Object bean = null;
        try {
            bean = createBeanInstance(beanDefinition, beanName, args);
            // 给 Bean 填充属性
            applyPropertyValues(beanName, bean, beanDefinition);

            // 执行 Bean 的初始化方法和 BeanPostProcessor 的前置和后置处理方法
            bean = initializeBean(beanName, bean, beanDefinition);
        } catch (Exception e) {
            throw new BeansException("Instantiation of bean failed", e);
        }

        addSingleton(beanName, bean);
        return bean;
    }

    /**
     * Bean 属性填充
     */
    protected void applyPropertyValues(String beanName, Object bean, BeanDefinition beanDefinition) {
        try {
            PropertyValues propertyValues = beanDefinition.getPropertyValues();
            for (PropertyValue propertyValue : propertyValues.getPropertyValues()) {

                String name = propertyValue.getName();
                Object value = propertyValue.getValue();

                if (value instanceof BeanReference) {
                    // A 依赖 B，获取 B 的实例化
                    BeanReference beanReference = (BeanReference) value;
                    value = getBean(beanReference.getBeanName());
                }
                // 属性填充
                BeanUtil.setFieldValue(bean, name, value);
            }
        } catch (Exception e) {
            throw new BeansException("Error setting property values：" + beanName);
        }
    }

    protected Object createBeanInstance(BeanDefinition beanDefinition, String beanName, Object[] args) {
        Constructor constructorToUse = null;
        Class<?> beanClass = beanDefinition.getBeanClass();
        Constructor<?>[] declaredConstructors = beanClass.getDeclaredConstructors();
        for (Constructor ctor : declaredConstructors) {
            if (null != args && ctor.getParameterTypes().length == args.length) {
                constructorToUse = ctor;
                break;
            }
        }
        return getInstantiationStrategy().instantiate(beanDefinition, beanName, constructorToUse, args);
    }

    public InstantiationStrategy getInstantiationStrategy() {
        return instantiationStrategy;
    }

    public void setInstantiationStrategy(InstantiationStrategy instantiationStrategy) {
        this.instantiationStrategy = instantiationStrategy;
    }

    private Object initializeBean(String beanName, Object bean, BeanDefinition beanDefinition) {
        // 1. 执行 BeanPostProcessor Before 处理
        Object wrappedBean = applyBeanPostProcessorsBeforeInitialization(bean, beanName);

        // 执行 Bean 对象的初始化方法
        try {
            invokeInitMethods(beanName, wrappedBean, beanDefinition);
        } catch (Exception e) {
            throw new BeansException("Invocation of init method of bean[" + beanName + "] failed", e);
        }
        // 2. 执行 BeanPostProcessor After 处理
        wrappedBean = applyBeanPostProcessorsAfterInitialization(wrappedBean, beanName);
        return wrappedBean;
    }

    private void invokeInitMethods(String beanName, Object bean, BeanDefinition beanDefinition) throws Exception {
        // 1. 实现接口 InitializingBean
        if (bean instanceof InitializingBean) {
            ((InitializingBean) bean).afterPropertiesSet();
        }

        // 2. 注解配置 init-method {判断是为了避免二次执行初始化}
        String initMethodName = beanDefinition.getInitMethodName();
        if (StrUtil.isNotEmpty(initMethodName) && !(bean instanceof InitializingBean)) {
            Method initMethod = beanDefinition.getBeanClass().getMethod(initMethodName);
            if (null == initMethod) {
                throw new BeansException("Could not find an init method named '" + initMethodName + "' on bean with name '" + beanName + "'");
            }
            initMethod.invoke(bean);
        }
    }

    @Override
    public Object applyBeanPostProcessorsBeforeInitialization(Object existingBean, String beanName) throws BeansException {
        Object result = existingBean;
        for (BeanPostProcessor processor : getBeanPostProcessors()) {
            Object current = processor.postProcessBeforeInitialization(result, beanName);
            if (null == current) return result;
            result = current;
        }
        return result;
    }

    @Override
    public Object applyBeanPostProcessorsAfterInitialization(Object existingBean, String beanName) throws BeansException {
        Object result = existingBean;
        for (BeanPostProcessor processor : getBeanPostProcessors()) {
            Object current = processor.postProcessAfterInitialization(result, beanName);
            if (null == current) return result;
            result = current;
        }
        return result;
    }
}

public class XmlBeanDefinitionReader extends AbstractBeanDefinitionReader {

    public XmlBeanDefinitionReader(BeanDefinitionRegistry registry) {
        super(registry);
    }

    public XmlBeanDefinitionReader(BeanDefinitionRegistry registry, ResourceLoader resourceLoader) {
        super(registry, resourceLoader);
    }

    @Override
    public void loadBeanDefinitions(Resource resource) throws BeansException {
        try {
            try (InputStream inputStream = resource.getInputStream()) {
                doLoadBeanDefinitions(inputStream);
            }
        } catch (IOException | ClassNotFoundException e) {
            throw new BeansException("IOException parsing XML document from " + resource, e);
        }
    }

    @Override
    public void loadBeanDefinitions(Resource... resources) throws BeansException {
        for (Resource resource : resources) {
            loadBeanDefinitions(resource);
        }
    }

    @Override
    public void loadBeanDefinitions(String location) throws BeansException {
        ResourceLoader resourceLoader = getResourceLoader();
        Resource resource = resourceLoader.getResource(location);
        loadBeanDefinitions(resource);
    }

    @Override
    public void loadBeanDefinitions(String... locations) throws BeansException {
        for (String location : locations) {
            loadBeanDefinitions(location);
        }
    }

    protected void doLoadBeanDefinitions(InputStream inputStream) throws ClassNotFoundException {
        Document doc = XmlUtil.readXML(inputStream);
        Element root = doc.getDocumentElement();
        NodeList childNodes = root.getChildNodes();

        for (int i = 0; i < childNodes.getLength(); i++) {
            // 判断元素
            if (!(childNodes.item(i) instanceof Element)) continue;
            // 判断对象
            if (!"bean".equals(childNodes.item(i).getNodeName())) continue;

            // 解析标签
            Element bean = (Element) childNodes.item(i);
            String id = bean.getAttribute("id");
            String name = bean.getAttribute("name");
            String className = bean.getAttribute("class");
            String initMethod = bean.getAttribute("init-method");
            String destroyMethodName = bean.getAttribute("destroy-method");

            // 获取 Class，方便获取类中的名称
            Class<?> clazz = Class.forName(className);
            // 优先级 id > name
            String beanName = StrUtil.isNotEmpty(id) ? id : name;
            if (StrUtil.isEmpty(beanName)) {
                beanName = StrUtil.lowerFirst(clazz.getSimpleName());
            }

            // 定义Bean
            BeanDefinition beanDefinition = new BeanDefinition(clazz);
            beanDefinition.setInitMethodName(initMethod);
            beanDefinition.setDestroyMethodName(destroyMethodName);

            // 读取属性并填充
            for (int j = 0; j < bean.getChildNodes().getLength(); j++) {
                if (!(bean.getChildNodes().item(j) instanceof Element)) continue;
                if (!"property".equals(bean.getChildNodes().item(j).getNodeName())) continue;
                // 解析标签：property
                Element property = (Element) bean.getChildNodes().item(j);
                String attrName = property.getAttribute("name");
                String attrValue = property.getAttribute("value");
                String attrRef = property.getAttribute("ref");
                // 获取属性值：引入对象、值对象
                Object value = StrUtil.isNotEmpty(attrRef) ? new BeanReference(attrRef) : attrValue;
                // 创建属性信息
                PropertyValue propertyValue = new PropertyValue(attrName, value);
                beanDefinition.getPropertyValues().addPropertyValue(propertyValue);
            }
            if (getRegistry().containsBeanDefinition(beanName)) {
                throw new BeansException("Duplicate beanName[" + beanName + "] is not allowed");
            }
            // 注册 BeanDefinition
            getRegistry().registerBeanDefinition(beanName, beanDefinition);
        }
    }
}

 

测试代码

public class UserDao {

    private static Map<String, String> hashMap = new HashMap<>();

    public void initDataMethod(){
        System.out.println("执行：init-method");
        hashMap.put("1", "a");
        hashMap.put("2", "b");
        hashMap.put("3", "c");
    }

    public void destroyDataMethod(){
        System.out.println("执行：destroy-method");
        hashMap.clear();
    }

    public String queryUserName(String uId) {
        return hashMap.get(uId);
    }

}

public class UserService implements InitializingBean, DisposableBean {

    private String uId;
    private String company;
    private String location;
    private UserDao userDao;

    @Override
    public void destroy() throws Exception {
        System.out.println("执行：UserService.destroy");
    }

    @Override
    public void afterPropertiesSet() throws Exception {
        System.out.println("执行：UserService.afterPropertiesSet");
    }

    public String queryUserInfo() {
        return userDao.queryUserName(uId) + "," + company + "," + location;
    }

    public String getuId() {
        return uId;
    }

    public void setuId(String uId) {
        this.uId = uId;
    }

    public String getCompany() {
        return company;
    }

    public void setCompany(String company) {
        this.company = company;
    }

    public String getLocation() {
        return location;
    }

    public void setLocation(String location) {
        this.location = location;
    }

    public UserDao getUserDao() {
        return userDao;
    }

    public void setUserDao(UserDao userDao) {
        this.userDao = userDao;
    }


}


public class MyBeanFactoryPostProcessor implements BeanFactoryPostProcessor {

    @Override
    public void postProcessBeanFactory(ConfigurableListableBeanFactory beanFactory) throws BeansException {

        BeanDefinition beanDefinition = beanFactory.getBeanDefinition("userService");
        PropertyValues propertyValues = beanDefinition.getPropertyValues();

        propertyValues.addPropertyValue(new PropertyValue("company", "改为：字节跳动"));
    }

}

public class MyBeanPostProcessor implements BeanPostProcessor {

    @Override
    public Object postProcessBeforeInitialization(Object bean, String beanName) throws BeansException {
        if ("userService".equals(beanName)) {
            UserService userService = (UserService) bean;
            userService.setLocation("改为：北京");
        }
        return bean;
    }

    @Override
    public Object postProcessAfterInitialization(Object bean, String beanName) throws BeansException {
        return bean;
    }

}


public class BeanFactoryTest extends TestCase {
    @Test
    public void test_xml() {
        // 1.初始化 BeanFactory
        ClassPathXmlApplicationContext applicationContext = new ClassPathXmlApplicationContext("classpath:springPostProcessor.xml");
        applicationContext.registerShutdownHook();

        // 2. 获取Bean对象调用方法
        UserService userService = applicationContext.getBean("userService", UserService.class);
        String result = userService.queryUserInfo();
        System.out.println("测试结果：" + result);
    }

    @Test
    public void test_hook() {
        Runtime.getRuntime().addShutdownHook(new Thread(() -> System.out.println("close！")));
    }

}

测试xml

<?xml version="1.0" encoding="UTF-8"?>
<beans>

    <bean id="userDao" class="springframework.bean.UserDao" init-method="initDataMethod" destroy-method="destroyDataMethod"/>

    <bean id="userService" class="springframework.bean.UserService">
        <property name="uId" value="1"/>
        <property name="company" value="haha"/>
        <property name="location" value="22"/>
        <property name="userDao" ref="userDao"/>
    </bean>

    <bean class="springframework.common.MyBeanPostProcessor"/>
    <bean class="springframework.common.MyBeanFactoryPostProcessor"/>

</beans>

 

 

版本V7.0 定义标记类型Aware接口，实现感知容器对象

 

实现Aware接口，在bean初始化的时候，根据bean classtype 设置数据。

public abstract class AbstractApplicationContext extends DefaultResourceLoader implements ConfigurableApplicationContext {

    @Override
    public void refresh() throws BeansException {
        // 1. 创建 BeanFactory，并加载 BeanDefinition
        refreshBeanFactory();

        // 2. 获取 BeanFactory
        ConfigurableListableBeanFactory beanFactory = getBeanFactory();

        // 3. 添加 ApplicationContextAwareProcessor，让继承自 ApplicationContextAware 的 Bean 对象都能感知所属的 ApplicationContext
        beanFactory.addBeanPostProcessor(new ApplicationContextAwareProcessor(this));

        // 4. 在 Bean 实例化之前，执行 BeanFactoryPostProcessor (Invoke factory processors registered as beans in the context.)
        invokeBeanFactoryPostProcessors(beanFactory);

        // 5. BeanPostProcessor 需要提前于其他 Bean 对象实例化之前执行注册操作
        registerBeanPostProcessors(beanFactory);

        // 6. 提前实例化单例Bean对象
        beanFactory.preInstantiateSingletons();
    }

    protected abstract void refreshBeanFactory() throws BeansException;

    protected abstract ConfigurableListableBeanFactory getBeanFactory();

    private void invokeBeanFactoryPostProcessors(ConfigurableListableBeanFactory beanFactory) {
        Map<String, BeanFactoryPostProcessor> beanFactoryPostProcessorMap = beanFactory.getBeansOfType(BeanFactoryPostProcessor.class);
        for (BeanFactoryPostProcessor beanFactoryPostProcessor : beanFactoryPostProcessorMap.values()) {
            beanFactoryPostProcessor.postProcessBeanFactory(beanFactory);
        }
    }

    private void registerBeanPostProcessors(ConfigurableListableBeanFactory beanFactory) {
        Map<String, BeanPostProcessor> beanPostProcessorMap = beanFactory.getBeansOfType(BeanPostProcessor.class);
        for (BeanPostProcessor beanPostProcessor : beanPostProcessorMap.values()) {
            beanFactory.addBeanPostProcessor(beanPostProcessor);
        }
    }

    @Override
    public <T> Map<String, T> getBeansOfType(Class<T> type) throws BeansException {
        return getBeanFactory().getBeansOfType(type);
    }

    @Override
    public String[] getBeanDefinitionNames() {
        return getBeanFactory().getBeanDefinitionNames();
    }

    @Override
    public Object getBean(String name) throws BeansException {
        return getBeanFactory().getBean(name);
    }

    @Override
    public Object getBean(String name, Object... args) throws BeansException {
        return getBeanFactory().getBean(name, args);
    }

    @Override
    public <T> T getBean(String name, Class<T> requiredType) throws BeansException {
        return getBeanFactory().getBean(name, requiredType);
    }

    @Override
    public void registerShutdownHook() {
        Runtime.getRuntime().addShutdownHook(new Thread(this::close));
    }

    @Override
    public void close() {
        getBeanFactory().destroySingletons();
    }

}

public class ApplicationContextAwareProcessor implements BeanPostProcessor {

    private final ApplicationContext applicationContext;

    public ApplicationContextAwareProcessor(ApplicationContext applicationContext) {
        this.applicationContext = applicationContext;
    }

    @Override
    public Object postProcessBeforeInitialization(Object bean, String beanName) throws BeansException {
        if (bean instanceof ApplicationContextAware){
            ((ApplicationContextAware) bean).setApplicationContext(applicationContext);
        }
        return bean;
    }

    @Override
    public Object postProcessAfterInitialization(Object bean, String beanName) throws BeansException {
        return bean;
    }

}

public abstract class AbstractAutowireCapableBean extends AbstractBeanFactory implements AutowireCapableBeanFactory {


    private InstantiationStrategy instantiationStrategy = new CglibSubclassingInstantiationStrategy();

    @Override
    protected Object createBean(String beanName, BeanDefinition beanDefinition, Object[] args) throws BeansException {
        Object bean = null;
        try {
            bean = createBeanInstance(beanDefinition, beanName, args);
            // 给 Bean 填充属性
            applyPropertyValues(beanName, bean, beanDefinition);

            // 执行 Bean 的初始化方法和 BeanPostProcessor 的前置和后置处理方法
            bean = initializeBean(beanName, bean, beanDefinition);
        } catch (Exception e) {
            throw new BeansException("Instantiation of bean failed", e);
        }

        addSingleton(beanName, bean);
        return bean;
    }

    /**
     * Bean 属性填充
     */
    protected void applyPropertyValues(String beanName, Object bean, BeanDefinition beanDefinition) {
        try {
            PropertyValues propertyValues = beanDefinition.getPropertyValues();
            for (PropertyValue propertyValue : propertyValues.getPropertyValues()) {

                String name = propertyValue.getName();
                Object value = propertyValue.getValue();

                if (value instanceof BeanReference) {
                    // A 依赖 B，获取 B 的实例化
                    BeanReference beanReference = (BeanReference) value;
                    value = getBean(beanReference.getBeanName());
                }
                // 属性填充
                BeanUtil.setFieldValue(bean, name, value);
            }
        } catch (Exception e) {
            throw new BeansException("Error setting property values：" + beanName);
        }
    }

    protected Object createBeanInstance(BeanDefinition beanDefinition, String beanName, Object[] args) {
        Constructor constructorToUse = null;
        Class<?> beanClass = beanDefinition.getBeanClass();
        Constructor<?>[] declaredConstructors = beanClass.getDeclaredConstructors();
        for (Constructor ctor : declaredConstructors) {
            if (null != args && ctor.getParameterTypes().length == args.length) {
                constructorToUse = ctor;
                break;
            }
        }
        return getInstantiationStrategy().instantiate(beanDefinition, beanName, constructorToUse, args);
    }

    public InstantiationStrategy getInstantiationStrategy() {
        return instantiationStrategy;
    }

    public void setInstantiationStrategy(InstantiationStrategy instantiationStrategy) {
        this.instantiationStrategy = instantiationStrategy;
    }

    private Object initializeBean(String beanName, Object bean, BeanDefinition beanDefinition) {
        // invokeAwareMethods
        if (bean instanceof Aware) {
            if (bean instanceof BeanFactoryAware) {
                ((BeanFactoryAware) bean).setBeanFactory(this);
            }
            if (bean instanceof BeanClassLoaderAware){
                ((BeanClassLoaderAware) bean).setBeanClassLoader(getBeanClassLoader());
            }
            if (bean instanceof BeanNameAware) {
                ((BeanNameAware) bean).setBeanName(beanName);
            }
        }

        // 1. 执行 BeanPostProcessor Before 处理
        Object wrappedBean = applyBeanPostProcessorsBeforeInitialization(bean, beanName);

        // 执行 Bean 对象的初始化方法
        try {
            invokeInitMethods(beanName, wrappedBean, beanDefinition);
        } catch (Exception e) {
            throw new BeansException("Invocation of init method of bean[" + beanName + "] failed", e);
        }
        // 2. 执行 BeanPostProcessor After 处理
        wrappedBean = applyBeanPostProcessorsAfterInitialization(wrappedBean, beanName);
        return wrappedBean;
    }

    private void invokeInitMethods(String beanName, Object bean, BeanDefinition beanDefinition) throws Exception {
        // 1. 实现接口 InitializingBean
        if (bean instanceof InitializingBean) {
            ((InitializingBean) bean).afterPropertiesSet();
        }

        // 2. 注解配置 init-method {判断是为了避免二次执行初始化}
        String initMethodName = beanDefinition.getInitMethodName();
        if (StrUtil.isNotEmpty(initMethodName) && !(bean instanceof InitializingBean)) {
            Method initMethod = beanDefinition.getBeanClass().getMethod(initMethodName);
            if (null == initMethod) {
                throw new BeansException("Could not find an init method named '" + initMethodName + "' on bean with name '" + beanName + "'");
            }
            initMethod.invoke(bean);
        }
    }

    @Override
    public Object applyBeanPostProcessorsBeforeInitialization(Object existingBean, String beanName) throws BeansException {
        Object result = existingBean;
        for (BeanPostProcessor processor : getBeanPostProcessors()) {
            Object current = processor.postProcessBeforeInitialization(result, beanName);
            if (null == current) return result;
            result = current;
        }
        return result;
    }

    @Override
    public Object applyBeanPostProcessorsAfterInitialization(Object existingBean, String beanName) throws BeansException {
        Object result = existingBean;
        for (BeanPostProcessor processor : getBeanPostProcessors()) {
            Object current = processor.postProcessAfterInitialization(result, beanName);
            if (null == current) return result;
            result = current;
        }
        return result;
    }
}

 

测试代码

public class UserService implements BeanNameAware, BeanClassLoaderAware, ApplicationContextAware, BeanFactoryAware {

    private ApplicationContext applicationContext;
    private BeanFactory beanFactory;

    private String uId;
    private String company;
    private String location;
    private UserDao userDao;

    @Override
    public void setBeanFactory(BeanFactory beanFactory) throws BeansException {
        this.beanFactory = beanFactory;
    }

    @Override
    public void setApplicationContext(ApplicationContext applicationContext) throws BeansException {
        this.applicationContext = applicationContext;
    }

    @Override
    public void setBeanName(String name) {
        System.out.println("Bean Name is：" + name);
    }

    @Override
    public void setBeanClassLoader(ClassLoader classLoader) {
        System.out.println("ClassLoader：" + classLoader);
    }

    public String queryUserInfo() {
        return userDao.queryUserName(uId) + "," + company + "," + location;
    }

    public String getuId() {
        return uId;
    }

    public void setuId(String uId) {
        this.uId = uId;
    }

    public String getCompany() {
        return company;
    }

    public void setCompany(String company) {
        this.company = company;
    }

    public String getLocation() {
        return location;
    }

    public void setLocation(String location) {
        this.location = location;
    }

    public UserDao getUserDao() {
        return userDao;
    }

    public void setUserDao(UserDao userDao) {
        this.userDao = userDao;
    }


    public ApplicationContext getApplicationContext() {
        return applicationContext;
    }

    public BeanFactory getBeanFactory() {
        return beanFactory;
    }

}
public class BeanFactoryTest extends TestCase {
    @Test
    public void test_xml() {
        // 1.初始化 BeanFactory
        ClassPathXmlApplicationContext applicationContext = new ClassPathXmlApplicationContext("classpath:spring.xml");
        applicationContext.registerShutdownHook();

        // 2. 获取Bean对象调用方法
        UserService userService = applicationContext.getBean("userService", UserService.class);
        String result = userService.queryUserInfo();
        System.out.println("测试结果：" + result);

        System.out.println("ApplicationContextAware："+userService.getApplicationContext());
        System.out.println("BeanFactoryAware："+userService.getBeanFactory());
 }
 
}

ps:

在具体的接口实现过程中你可以看到，一部分(BeanFactoryAware、BeanClassLoaderAware、BeanNameAware)在 factory 的 support 文件夹下，另外 ApplicationContextAware 是在 context 的 support 中，这是因为不同的内容获取需要在不同的包下提供。所以，在 AbstractApplicationContext 的具体实现中会用到向 beanFactory 添加 BeanPostProcessor 内容的 ApplicationContextAwareProcessor 操作，最后由 AbstractAutowireCapableBeanFactory 创建 createBean 时处理相应的调用操作。 

 

版本V8.0 关于Bean对象作用域以及FactoryBean的实现和使用 

 

 

 

FactoryBean：是实现了 FactoryBean<T> 接⼝的Bean，根据该Bean的ID从BeanFactory中获取的实际上是FactoryBean的getObject()返回的对象，⽽不是FactoryBean本身，如果要获取FactoryBean对象，请在id前⾯加⼀个&符号来获取。

 

思路：在beanDefinition中增加scope属性，决定是否使用单例缓存; getBean()时如果发现bean是FactoryBean，使用getObject(),替代createBean();

public abstract class AbstractBeanFactory extends FactoryBeanRegistrySupport implements ConfigurableBeanFactory {

    private ClassLoader beanClassLoader = ClassUtils.getDefaultClassLoader();


    private final List<BeanPostProcessor> beanPostProcessors = new ArrayList<>();

    @Override
    public Object getBean(String name) throws BeansException {
        return doGetBean(name, null);
    }

    @Override
    public Object getBean(String name, Object... args) throws BeansException {
        return doGetBean(name, args);
    }

    @Override
    public <T> T getBean(String name, Class<T> requiredType) throws BeansException {
        return (T) getBean(name);
    }

    protected <T> T doGetBean(final String name, final Object[] args) {
        Object sharedInstance = getSingleton(name);
        if (sharedInstance != null) {
            // 如果是 FactoryBean，则需要调用 FactoryBean#getObject
            return (T) getObjectForBeanInstance(sharedInstance, name);
        }

        BeanDefinition beanDefinition = getBeanDefinition(name);
        Object bean = createBean(name, beanDefinition, args);
        return (T) getObjectForBeanInstance(bean, name);
    }

    private Object getObjectForBeanInstance(Object beanInstance, String beanName) {
        if (!(beanInstance instanceof FactoryBean)) {
            return beanInstance;
        }

        Object object = getCachedObjectForFactoryBean(beanName);

        if (object == null) {
            FactoryBean<?> factoryBean = (FactoryBean<?>) beanInstance;
            object = getObjectFromFactoryBean(factoryBean, beanName);
        }

        return object;
    }

    protected abstract BeanDefinition getBeanDefinition(String beanName) throws BeansException;

    protected abstract Object createBean(String beanName, BeanDefinition beanDefinition, Object[] args) throws BeansException;

    @Override
    public void addBeanPostProcessor(BeanPostProcessor beanPostProcessor){
        this.beanPostProcessors.remove(beanPostProcessor);
        this.beanPostProcessors.add(beanPostProcessor);
    }

    public List<BeanPostProcessor> getBeanPostProcessors() {
        return this.beanPostProcessors;
    }

    public ClassLoader getBeanClassLoader() {
        return this.beanClassLoader;
    }

}

public abstract class FactoryBeanRegistrySupport extends DefaultSingletonBeanRegistry {

    /**
     * Cache of singleton objects created by FactoryBeans: FactoryBean name --> object
     */
    private final Map<String, Object> factoryBeanObjectCache = new ConcurrentHashMap<String, Object>();

    protected Object getCachedObjectForFactoryBean(String beanName) {
        Object object = this.factoryBeanObjectCache.get(beanName);
        return (object != NULL_OBJECT ? object : null);
    }

    protected Object getObjectFromFactoryBean(FactoryBean factory, String beanName) {
        if (factory.isSingleton()) {
            Object object = this.factoryBeanObjectCache.get(beanName);
            if (object == null) {
                object = doGetObjectFromFactoryBean(factory, beanName);
                this.factoryBeanObjectCache.put(beanName, (object != null ? object : NULL_OBJECT));
            }
            return (object != NULL_OBJECT ? object : null);
        } else {
            return doGetObjectFromFactoryBean(factory, beanName);
        }
    }

    private Object doGetObjectFromFactoryBean(final FactoryBean factory, final String beanName){
        try {
            return factory.getObject();
        } catch (Exception e) {
            throw new BeansException("FactoryBean threw exception on object[" + beanName + "] creation", e);
        }
    }

}

public abstract class AbstractAutowireCapableBean extends AbstractBeanFactory implements AutowireCapableBeanFactory {


    private InstantiationStrategy instantiationStrategy = new SimpleInstantiationStrategy();

    @Override
    protected Object createBean(String beanName, BeanDefinition beanDefinition, Object[] args) throws BeansException {
        Object bean = null;
        try {
            bean = createBeanInstance(beanDefinition, beanName, args);
            // 给 Bean 填充属性
            applyPropertyValues(beanName, bean, beanDefinition);

            // 执行 Bean 的初始化方法和 BeanPostProcessor 的前置和后置处理方法
            bean = initializeBean(beanName, bean, beanDefinition);
        } catch (Exception e) {
            throw new BeansException("Instantiation of bean failed", e);
        }

        // 注册实现了 DisposableBean 接口的 Bean 对象
        registerDisposableBeanIfNecessary(beanName, bean, beanDefinition);

        // 判断 SCOPE_SINGLETON、SCOPE_PROTOTYPE
        if (beanDefinition.isSingleton()) {
            addSingleton(beanName, bean);
        }
        return bean;
    }
}

 

 

版本V9.0 基于观察者实现，容器事件和事件监听器 

 

 

 

在整个功能实现过程中，仍然需要在面向用户的应用上下文 AbstractApplicationContext 中添加相关事件内容，包括：初始化事件发布者、注册事件监听器、发布容器刷新完成事件。

使用观察者模式定义事件类、监听类、发布类，同时还需要完成一个广播器的功能，接收到事件推送时进行分析处理符合监听事件接受者感兴趣的事件，也就是使用 isAssignableFrom 进行判断。

 

理解event包下消息发布、监听机制。在AbstractApplicationContext.refresh()中实现监听机制。

 

public abstract class AbstractApplicationContext extends DefaultResourceLoader implements ConfigurableApplicationContext {


    public static final String APPLICATION_EVENT_MULTICASTER_BEAN_NAME = "applicationEventMulticaster";

    private ApplicationEventMulticaster applicationEventMulticaster;

    @Override
    public void refresh() throws BeansException {
        // 1. 创建 BeanFactory，并加载 BeanDefinition
        refreshBeanFactory();

        // 2. 获取 BeanFactory
        ConfigurableListableBeanFactory beanFactory = getBeanFactory();

        // 3. 添加 ApplicationContextAwareProcessor，让继承自 ApplicationContextAware 的 Bean 对象都能感知所属的 ApplicationContext
        beanFactory.addBeanPostProcessor(new ApplicationContextAwareProcessor(this));

        // 4. 在 Bean 实例化之前，执行 BeanFactoryPostProcessor (Invoke factory processors registered as beans in the context.)
        invokeBeanFactoryPostProcessors(beanFactory);

        // 5. BeanPostProcessor 需要提前于其他 Bean 对象实例化之前执行注册操作
        registerBeanPostProcessors(beanFactory);


        // 6. 初始化事件发布者
        initApplicationEventMulticaster();

        // 7. 注册事件监听器
        registerListeners();

        // 8. 提前实例化单例Bean对象
        beanFactory.preInstantiateSingletons();

        // 9. 发布容器刷新完成事件
        finishRefresh();
    }

    protected abstract void refreshBeanFactory() throws BeansException;

    protected abstract ConfigurableListableBeanFactory getBeanFactory();

    private void invokeBeanFactoryPostProcessors(ConfigurableListableBeanFactory beanFactory) {
        Map<String, BeanFactoryPostProcessor> beanFactoryPostProcessorMap = beanFactory.getBeansOfType(BeanFactoryPostProcessor.class);
        for (BeanFactoryPostProcessor beanFactoryPostProcessor : beanFactoryPostProcessorMap.values()) {
            beanFactoryPostProcessor.postProcessBeanFactory(beanFactory);
        }
    }

    private void registerBeanPostProcessors(ConfigurableListableBeanFactory beanFactory) {
        Map<String, BeanPostProcessor> beanPostProcessorMap = beanFactory.getBeansOfType(BeanPostProcessor.class);
        for (BeanPostProcessor beanPostProcessor : beanPostProcessorMap.values()) {
            beanFactory.addBeanPostProcessor(beanPostProcessor);
        }
    }

    @Override
    public <T> Map<String, T> getBeansOfType(Class<T> type) throws BeansException {
        return getBeanFactory().getBeansOfType(type);
    }

    @Override
    public String[] getBeanDefinitionNames() {
        return getBeanFactory().getBeanDefinitionNames();
    }

    @Override
    public Object getBean(String name) throws BeansException {
        return getBeanFactory().getBean(name);
    }

    @Override
    public Object getBean(String name, Object... args) throws BeansException {
        return getBeanFactory().getBean(name, args);
    }

    @Override
    public <T> T getBean(String name, Class<T> requiredType) throws BeansException {
        return getBeanFactory().getBean(name, requiredType);
    }

    @Override
    public void registerShutdownHook() {
        Runtime.getRuntime().addShutdownHook(new Thread(this::close));
    }

    @Override
    public void close() {
        getBeanFactory().destroySingletons();
    }

    private void initApplicationEventMulticaster() {
        ConfigurableListableBeanFactory beanFactory = getBeanFactory();
        applicationEventMulticaster = new SimpleApplicationEventMulticaster(beanFactory);
        beanFactory.registerSingleton(APPLICATION_EVENT_MULTICASTER_BEAN_NAME, applicationEventMulticaster);
    }

    private void registerListeners() {
        Collection<ApplicationListener> applicationListeners = getBeansOfType(ApplicationListener.class).values();
        for (ApplicationListener listener : applicationListeners) {
            applicationEventMulticaster.addApplicationListener(listener);
        }
    }

    private void finishRefresh() {
        publishEvent(new ContextRefreshedEvent(this));
    }

    @Override
    public void publishEvent(ApplicationEvent event) {
        applicationEventMulticaster.multicastEvent(event);
    }
}

public abstract class AbstractApplicationEventMulticaster implements ApplicationEventMulticaster, BeanFactoryAware {

    public final Set<ApplicationListener<ApplicationEvent>> applicationListeners = new LinkedHashSet<>();

    private BeanFactory beanFactory;

    @Override
    public void addApplicationListener(ApplicationListener<?> listener) {
        applicationListeners.add((ApplicationListener<ApplicationEvent>) listener);
    }

    @Override
    public void removeApplicationListener(ApplicationListener<?> listener) {
        applicationListeners.remove(listener);
    }

    @Override
    public final void setBeanFactory(BeanFactory beanFactory) {
        this.beanFactory = beanFactory;
    }

    /**
     * Return a Collection of ApplicationListeners matching the given
     * event type. Non-matching listeners get excluded early.
     * @param event the event to be propagated. Allows for excluding
     * non-matching listeners early, based on cached matching information.
     * @return a Collection of ApplicationListeners
     * @see cn.bugstack.springframework.context.ApplicationListener
     */
    protected Collection<ApplicationListener> getApplicationListeners(ApplicationEvent event) {
        LinkedList<ApplicationListener> allListeners = new LinkedList<ApplicationListener>();
        for (ApplicationListener<ApplicationEvent> listener : applicationListeners) {
            if (supportsEvent(listener, event)) allListeners.add(listener);
        }
        return allListeners;
    }

    /**
     * 监听器是否对该事件感兴趣
     */
    protected boolean supportsEvent(ApplicationListener<ApplicationEvent> applicationListener, ApplicationEvent event) {
        Class<? extends ApplicationListener> listenerClass = applicationListener.getClass();

        // 按照 CglibSubclassingInstantiationStrategy、SimpleInstantiationStrategy 不同的实例化类型，需要判断后获取目标 class
        Class<?> targetClass = ClassUtils.isCglibProxyClass(listenerClass) ? listenerClass.getSuperclass() : listenerClass;
        Type genericInterface = targetClass.getGenericInterfaces()[0];

        Type actualTypeArgument = ((ParameterizedType) genericInterface).getActualTypeArguments()[0];
        String className = actualTypeArgument.getTypeName();
        Class<?> eventClassName;
        try {
            eventClassName = Class.forName(className);
        } catch (ClassNotFoundException e) {
            throw new BeansException("wrong event class name: " + className);
        }
        // 判定此 eventClassName 对象所表示的类或接口与指定的 event.getClass() 参数所表示的类或接口是否相同，或是否是其超类或超接口。
        // isAssignableFrom是用来判断子类和父类的关系的，或者接口的实现类和接口的关系的，默认所有的类的终极父类都是Object。如果A.isAssignableFrom(B)结果是true，证明B可以转换成为A,也就是A可以由B转换而来。
        return eventClassName.isAssignableFrom(event.getClass());
    }

}

public class ApplicationContextEvent extends ApplicationEvent {

    /**
     * Constructs a prototypical Event.
     *
     * @param source The object on which the Event initially occurred.
     * @throws IllegalArgumentException if source is null.
     */
    public ApplicationContextEvent(Object source) {
        super(source);
    }

    /**
     * Get the <code>ApplicationContext</code> that the event was raised for.
     */
    public final ApplicationContext getApplicationContext() {
        return (ApplicationContext) getSource();
    }

}

public interface ApplicationEventMulticaster {

    /**
     * Add a listener to be notified of all events.
     * @param listener the listener to add
     */
    void addApplicationListener(ApplicationListener<?> listener);

    /**
     * Remove a listener from the notification list.
     * @param listener the listener to remove
     */
    void removeApplicationListener(ApplicationListener<?> listener);

    /**
     * Multicast the given application event to appropriate listeners.
     * @param event the event to multicast
     */
    void multicastEvent(ApplicationEvent event);

}

public class ContextClosedEvent extends ApplicationContextEvent{

    /**
     * Constructs a prototypical Event.
     *
     * @param source The object on which the Event initially occurred.
     * @throws IllegalArgumentException if source is null.
     */
    public ContextClosedEvent(Object source) {
        super(source);
    }

}

public class ContextRefreshedEvent extends ApplicationContextEvent{
    /**
     * Constructs a prototypical Event.
     *
     * @param source The object on which the Event initially occurred.
     * @throws IllegalArgumentException if source is null.
     */
    public ContextRefreshedEvent(Object source) {
        super(source);
    }

}

public class SimpleApplicationEventMulticaster extends AbstractApplicationEventMulticaster {

    public SimpleApplicationEventMulticaster(BeanFactory beanFactory) {
        setBeanFactory(beanFactory);
    }

    @SuppressWarnings("unchecked")
    @Override
    public void multicastEvent(final ApplicationEvent event) {
        for (final ApplicationListener listener : getApplicationListeners(event)) {
            listener.onApplicationEvent(event);
        }
    }

}

 

测试代码

public class ContextClosedEventListener implements ApplicationListener<ContextClosedEvent> {

    @Override
    public void onApplicationEvent(ContextClosedEvent event) {
        System.out.println("关闭事件：" + this.getClass().getName());
    }
}

public class ContextRefreshedEventListener implements ApplicationListener<ContextRefreshedEvent> {

    @Override
    public void onApplicationEvent(ContextRefreshedEvent event) {
        System.out.println("刷新事件：" + this.getClass().getName());
    }

}

public class CustomEvent extends ApplicationContextEvent {

    private Long id;
    private String message;

    /**
     * Constructs a prototypical Event.
     *
     * @param source The object on which the Event initially occurred.
     * @throws IllegalArgumentException if source is null.
     */
    public CustomEvent(Object source, Long id, String message) {
        super(source);
        this.id = id;
        this.message = message;
    }

    public Long getId() {
        return id;
    }

    public void setId(Long id) {
        this.id = id;
    }

    public String getMessage() {
        return message;
    }

    public void setMessage(String message) {
        this.message = message;
    }
}

public class CustomEventListener implements ApplicationListener<CustomEvent> {

    @Override
    public void onApplicationEvent(CustomEvent event) {
        System.out.println("收到：" + event.getSource() + "消息;时间：" + new Date());
        System.out.println("消息：" + event.getId() + ":" + event.getMessage());
    }

}



测试方法
    @Test
    public void test_event() {
        ClassPathXmlApplicationContext applicationContext = new ClassPathXmlApplicationContext("classpath:spring1.xml");
        applicationContext.publishEvent(new CustomEvent(applicationContext, 1L, "成功了！"));

        applicationContext.registerShutdownHook();
    }
}

<?xml version="1.0" encoding="UTF-8"?>
<beans>

    <bean class="springframework.event.ContextRefreshedEventListener"/>

    <bean class="springframework.event.CustomEventListener"/>

    <bean class="springframework.event.ContextClosedEventListener"/>

</beans>

刷新事件：springframework.event.ContextRefreshedEventListener
收到：springframework.context.support.ClassPathXmlApplicationContext@6996db8消息;时间：Tue Mar 07 20:05:24 CST 2023
消息：1019129009086763:成功了！

 

版本V10.0 于JDK和Cglib动态代理，实现AOP核心功能 

 将复杂的代理实现过程 封装到AdviseSupport

public class AspectJExpressionPointcut implements Pointcut, ClassFilter, MethodMatcher {

    private static final Set<PointcutPrimitive> SUPPORTED_PRIMITIVES = new HashSet<PointcutPrimitive>();

    static {
        SUPPORTED_PRIMITIVES.add(PointcutPrimitive.EXECUTION);
    }

    private final PointcutExpression pointcutExpression;

    public AspectJExpressionPointcut(String expression) {
        PointcutParser pointcutParser = PointcutParser.getPointcutParserSupportingSpecifiedPrimitivesAndUsingSpecifiedClassLoaderForResolution(SUPPORTED_PRIMITIVES, this.getClass().getClassLoader());
        pointcutExpression = pointcutParser.parsePointcutExpression(expression);
    }

    @Override
    public boolean matches(Class<?> clazz) {
        return pointcutExpression.couldMatchJoinPointsInType(clazz);
    }

    @Override
    public boolean matches(Method method, Class<?> targetClass) {
        return pointcutExpression.matchesMethodExecution(method).alwaysMatches();
    }

    @Override
    public ClassFilter getClassFilter() {
        return this;
    }

    @Override
    public MethodMatcher getMethodMatcher() {
        return this;
    }

}

public interface AopProxy {

    Object getProxy();

}

public class Cglib2AopProxy implements AopProxy {

    private final AdvisedSupport advised;

    public Cglib2AopProxy(AdvisedSupport advised) {
        this.advised = advised;
    }

    @Override
    public Object getProxy() {
        Enhancer enhancer = new Enhancer();
        enhancer.setSuperclass(advised.getTargetSource().getTarget().getClass());
        enhancer.setInterfaces(advised.getTargetSource().getTargetClass());
        enhancer.setCallback(new DynamicAdvisedInterceptor(advised));
        return enhancer.create();
    }

    private static class DynamicAdvisedInterceptor implements MethodInterceptor {

        private final AdvisedSupport advised;

        public DynamicAdvisedInterceptor(AdvisedSupport advised) {
            this.advised = advised;
        }

        @Override
        public Object intercept(Object o, Method method, Object[] objects, MethodProxy methodProxy) throws Throwable {
            CglibMethodInvocation methodInvocation = new CglibMethodInvocation(advised.getTargetSource().getTarget(), method, objects, methodProxy);
            if (advised.getMethodMatcher().matches(method, advised.getTargetSource().getTarget().getClass())) {
                return advised.getMethodInterceptor().invoke(methodInvocation);
            }
            return methodInvocation.proceed();
        }
    }

    private static class CglibMethodInvocation extends ReflectiveMethodInvocation {

        private final MethodProxy methodProxy;

        public CglibMethodInvocation(Object target, Method method, Object[] arguments, MethodProxy methodProxy) {
            super(target, method, arguments);
            this.methodProxy = methodProxy;
        }

        @Override
        public Object proceed() throws Throwable {
            return this.methodProxy.invoke(this.target, this.arguments);
        }

    }

}

public class JdkDynamicAopProxy implements AopProxy, InvocationHandler {

    private final AdvisedSupport advised;

    public JdkDynamicAopProxy(AdvisedSupport advised) {
        this.advised = advised;
    }

    @Override
    public Object getProxy() {
        return Proxy.newProxyInstance(Thread.currentThread().getContextClassLoader(), advised.getTargetSource().getTargetClass(), this);
    }

    @Override
    public Object invoke(Object proxy, Method method, Object[] args) throws Throwable {
        if (advised.getMethodMatcher().matches(method, advised.getTargetSource().getTarget().getClass())) {
            MethodInterceptor methodInterceptor = advised.getMethodInterceptor();
            return methodInterceptor.invoke(new ReflectiveMethodInvocation(advised.getTargetSource().getTarget(), method, args));
        }
        return method.invoke(advised.getTargetSource().getTarget(), args);
    }

}

public class ReflectiveMethodInvocation implements MethodInvocation {

    // 目标对象
    protected final Object target;
    // 方法
    protected final Method method;
    // 入参
    protected final Object[] arguments;

    public ReflectiveMethodInvocation(Object target, Method method, Object[] arguments) {
        this.target = target;
        this.method = method;
        this.arguments = arguments;
    }

    @Override
    public Method getMethod() {
        return method;
    }

    @Override
    public Object[] getArguments() {
        return arguments;
    }

    @Override
    public Object proceed() throws Throwable {
        return method.invoke(target, arguments);
    }

    @Override
    public Object getThis() {
        return target;
    }

    @Override
    public AccessibleObject getStaticPart() {
        return method;
    }

}

public class AdvisedSupport {

    // 被代理的目标对象
    private TargetSource targetSource;
    // 方法拦截器
    private MethodInterceptor methodInterceptor;
    // 方法匹配器(检查目标方法是否符合通知条件)
    private MethodMatcher methodMatcher;

    public TargetSource getTargetSource() {
        return targetSource;
    }

    public void setTargetSource(TargetSource targetSource) {
        this.targetSource = targetSource;
    }

    public MethodInterceptor getMethodInterceptor() {
        return methodInterceptor;
    }

    public void setMethodInterceptor(MethodInterceptor methodInterceptor) {
        this.methodInterceptor = methodInterceptor;
    }

    public MethodMatcher getMethodMatcher() {
        return methodMatcher;
    }

    public void setMethodMatcher(MethodMatcher methodMatcher) {
        this.methodMatcher = methodMatcher;
    }
}

public interface ClassFilter {

    /**
     * Should the pointcut apply to the given interface or target class?
     * @param clazz the candidate target class
     * @return whether the advice should apply to the given target class
     */
    boolean matches(Class<?> clazz);

}

public interface MethodMatcher {

    /**
     * Perform static checking whether the given method matches. If this
     * @return whether or not this method matches statically
     */
    boolean matches(Method method, Class<?> targetClass);
    
}



public interface Pointcut {

    /**
     * Return the ClassFilter for this pointcut.
     *
     * @return the ClassFilter (never <code>null</code>)
     */
    ClassFilter getClassFilter();

    /**
     * Return the MethodMatcher for this pointcut.
     *
     * @return the MethodMatcher (never <code>null</code>)
     */
    MethodMatcher getMethodMatcher();

}

public class TargetSource {

    private final Object target;

    public TargetSource(Object target) {
        this.target = target;
    }

    /**
     * Return the type of targets returned by this {@link TargetSource}.
     * <p>Can return <code>null</code>, although certain usages of a
     * <code>TargetSource</code> might just work with a predetermined
     * target class.
     * @return the type of targets returned by this {@link TargetSource}
     */
    public Class<?>[] getTargetClass(){
        return this.target.getClass().getInterfaces();
    }

    /**
     * Return a target instance. Invoked immediately before the
     * AOP framework calls the "target" of an AOP method invocation.
     * @return the target object, which contains the joinpoint
     * @throws Exception if the target object can't be resolved
     */
    public Object getTarget(){
        return this.target;
    }
    
}

 

测试

 @Test
    public void test_proxy_class() {
        IUserService userService = (IUserService) Proxy.newProxyInstance(Thread.currentThread().getContextClassLoader(), new Class[]{IUserService.class}, (proxy, method, args) -> "你被代理了！");
        String result = userService.queryUserInfo();
        System.out.println("测试结果：" + result);
    }

    @Test
    public void test_proxy_method() {
        // 目标对象(可以替换成任何的目标对象)
        Object targetObj = new UserService();

        // AOP 代理
        IUserService proxy = (IUserService) Proxy.newProxyInstance(Thread.currentThread().getContextClassLoader(), targetObj.getClass().getInterfaces(), new InvocationHandler() {
            // 方法匹配器
            MethodMatcher methodMatcher = new AspectJExpressionPointcut("execution(* springframework.bean.IUserService.*(..))");

            @Override
            public Object invoke(Object proxy, Method method, Object[] args) throws Throwable {
                if (methodMatcher.matches(method, targetObj.getClass())) {
                    // 方法拦截器
                    MethodInterceptor methodInterceptor = invocation -> {
                        long start = System.currentTimeMillis();
                        try {
                            return invocation.proceed();
                        } finally {
                            System.out.println("监控 - Begin By AOP");
                            System.out.println("方法名称：" + invocation.getMethod().getName());
                            System.out.println("方法耗时：" + (System.currentTimeMillis() - start) + "ms");
                            System.out.println("监控 - End\r\n");
                        }
                    };
                    // 反射调用
                    return methodInterceptor.invoke(new ReflectiveMethodInvocation(targetObj, method, args));
                }
                return method.invoke(targetObj, args);
            }
        });

        String result = proxy.queryUserInfo();
        System.out.println("测试结果：" + result);

    }

    @Test
    public void test_dynamic() {
        // 目标对象
        IUserService userService = new UserService();
        // 组装代理信息
        AdvisedSupport advisedSupport = new AdvisedSupport();
        advisedSupport.setTargetSource(new TargetSource(userService));
        advisedSupport.setMethodInterceptor(new UserServiceInterceptor());
        advisedSupport.setMethodMatcher(new AspectJExpressionPointcut("execution(* springframework.bean.IUserService.*(..))"));

        // 代理对象(JdkDynamicAopProxy)
        IUserService proxy_jdk = (IUserService) new JdkDynamicAopProxy(advisedSupport).getProxy();
        // 测试调用
        System.out.println("测试结果：" + proxy_jdk.queryUserInfo());

        // 代理对象(Cglib2AopProxy)
        IUserService proxy_cglib = (IUserService) new Cglib2AopProxy(advisedSupport).getProxy();
        // 测试调用
        System.out.println("测试结果：" + proxy_cglib.register("花花"));
    }

 

 

版本V11.0 把AOP动态代理，融入到Bean的生命周期

利用V10版本的AOP能力，

在createBean时，在InstantiationAwareBeanPostProcessor中根据AspectJExpressionPointcutAdvisor判断是否需要代理目标类，如需代理，则返回代理对象。

public abstract class AbstractAutowireCapableBeanFactory extends AbstractBeanFactory implements AutowireCapableBeanFactory {

    private InstantiationStrategy instantiationStrategy = new CglibSubclassingInstantiationStrategy();

    @Override
    protected Object createBean(String beanName, BeanDefinition beanDefinition, Object[] args) throws BeansException {
        Object bean = null;
        try {
            // 判断是否返回代理 Bean 对象
            bean = resolveBeforeInstantiation(beanName, beanDefinition);
            if (null != bean) {
                return bean;
            }
            // 实例化 Bean
            bean = createBeanInstance(beanDefinition, beanName, args);
            // 给 Bean 填充属性
            applyPropertyValues(beanName, bean, beanDefinition);
            // 执行 Bean 的初始化方法和 BeanPostProcessor 的前置和后置处理方法
            bean = initializeBean(beanName, bean, beanDefinition);
        } catch (Exception e) {
            throw new BeansException("Instantiation of bean failed", e);
        }

        // 注册实现了 DisposableBean 接口的 Bean 对象
        registerDisposableBeanIfNecessary(beanName, bean, beanDefinition);

        // 判断 SCOPE_SINGLETON、SCOPE_PROTOTYPE
        if (beanDefinition.isSingleton()) {
            registerSingleton(beanName, bean);
        }
        return bean;
    }

    protected Object resolveBeforeInstantiation(String beanName, BeanDefinition beanDefinition) {
        Object bean = applyBeanPostProcessorsBeforeInstantiation(beanDefinition.getBeanClass(), beanName);
        if (null != bean) {
            bean = applyBeanPostProcessorsAfterInitialization(bean, beanName);
        }
        return bean;
    }

    protected Object applyBeanPostProcessorsBeforeInstantiation(Class<?> beanClass, String beanName) {
        for (BeanPostProcessor beanPostProcessor : getBeanPostProcessors()) {
            if (beanPostProcessor instanceof InstantiationAwareBeanPostProcessor) {
                Object result = ((InstantiationAwareBeanPostProcessor) beanPostProcessor).postProcessBeforeInstantiation(beanClass, beanName);
                if (null != result) return result;
            }
        }
        return null;
    }

    protected void registerDisposableBeanIfNecessary(String beanName, Object bean, BeanDefinition beanDefinition) {
        // 非 Singleton 类型的 Bean 不执行销毁方法
        if (!beanDefinition.isSingleton()) return;

        if (bean instanceof DisposableBean || StrUtil.isNotEmpty(beanDefinition.getDestroyMethodName())) {
            registerDisposableBean(beanName, new DisposableBeanAdapter(bean, beanName, beanDefinition));
        }
    }

    protected Object createBeanInstance(BeanDefinition beanDefinition, String beanName, Object[] args) {
        Constructor constructorToUse = null;
        Class<?> beanClass = beanDefinition.getBeanClass();
        Constructor<?>[] declaredConstructors = beanClass.getDeclaredConstructors();
        for (Constructor ctor : declaredConstructors) {
            if (null != args && ctor.getParameterTypes().length == args.length) {
                constructorToUse = ctor;
                break;
            }
        }
        return getInstantiationStrategy().instantiate(beanDefinition, beanName, constructorToUse, args);
    }

    /**
     * Bean 属性填充
     */
    protected void applyPropertyValues(String beanName, Object bean, BeanDefinition beanDefinition) {
        try {
            PropertyValues propertyValues = beanDefinition.getPropertyValues();
            for (PropertyValue propertyValue : propertyValues.getPropertyValues()) {

                String name = propertyValue.getName();
                Object value = propertyValue.getValue();

                if (value instanceof BeanReference) {
                    // A 依赖 B，获取 B 的实例化
                    BeanReference beanReference = (BeanReference) value;
                    value = getBean(beanReference.getBeanName());
                }
                // 属性填充
                BeanUtil.setFieldValue(bean, name, value);
            }
        } catch (Exception e) {
            throw new BeansException("Error setting property values：" + beanName);
        }
    }

    public InstantiationStrategy getInstantiationStrategy() {
        return instantiationStrategy;
    }

    public void setInstantiationStrategy(InstantiationStrategy instantiationStrategy) {
        this.instantiationStrategy = instantiationStrategy;
    }

    private Object initializeBean(String beanName, Object bean, BeanDefinition beanDefinition) {

        // invokeAwareMethods
        if (bean instanceof Aware) {
            if (bean instanceof BeanFactoryAware) {
                ((BeanFactoryAware) bean).setBeanFactory(this);
            }
            if (bean instanceof BeanClassLoaderAware) {
                ((BeanClassLoaderAware) bean).setBeanClassLoader(getBeanClassLoader());
            }
            if (bean instanceof BeanNameAware) {
                ((BeanNameAware) bean).setBeanName(beanName);
            }
        }

        // 1. 执行 BeanPostProcessor Before 处理
        Object wrappedBean = applyBeanPostProcessorsBeforeInitialization(bean, beanName);

        // 执行 Bean 对象的初始化方法
        try {
            invokeInitMethods(beanName, wrappedBean, beanDefinition);
        } catch (Exception e) {
            throw new BeansException("Invocation of init method of bean[" + beanName + "] failed", e);
        }

        // 2. 执行 BeanPostProcessor After 处理
        wrappedBean = applyBeanPostProcessorsAfterInitialization(wrappedBean, beanName);
        return wrappedBean;
    }

    private void invokeInitMethods(String beanName, Object bean, BeanDefinition beanDefinition) throws Exception {
        // 1. 实现接口 InitializingBean
        if (bean instanceof InitializingBean) {
            ((InitializingBean) bean).afterPropertiesSet();
        }

        // 2. 注解配置 init-method {判断是为了避免二次执行销毁}
        String initMethodName = beanDefinition.getInitMethodName();
        if (StrUtil.isNotEmpty(initMethodName)) {
            Method initMethod = beanDefinition.getBeanClass().getMethod(initMethodName);
            if (null == initMethod) {
                throw new BeansException("Could not find an init method named '" + initMethodName + "' on bean with name '" + beanName + "'");
            }
            initMethod.invoke(bean);
        }
    }

    @Override
    public Object applyBeanPostProcessorsBeforeInitialization(Object existingBean, String beanName) throws BeansException {
        Object result = existingBean;
        for (BeanPostProcessor processor : getBeanPostProcessors()) {
            Object current = processor.postProcessBeforeInitialization(result, beanName);
            if (null == current) return result;
            result = current;
        }
        return result;
    }

    @Override
    public Object applyBeanPostProcessorsAfterInitialization(Object existingBean, String beanName) throws BeansException {
        Object result = existingBean;
        for (BeanPostProcessor processor : getBeanPostProcessors()) {
            Object current = processor.postProcessAfterInitialization(result, beanName);
            if (null == current) return result;
            result = current;
        }
        return result;
    }

}

public interface InstantiationAwareBeanPostProcessor extends BeanPostProcessor {

    /**
     * Apply this BeanPostProcessor <i>before the target bean gets instantiated</i>.
     * The returned bean object may be a proxy to use instead of the target bean,
     * effectively suppressing default instantiation of the target bean.
     *
     * 在 Bean 对象执行初始化方法之前，执行此方法
     *
     * @param beanClass
     * @param beanName
     * @return
     * @throws BeansException
     */
    Object postProcessBeforeInstantiation(Class<?> beanClass, String beanName) throws BeansException;

}

public class ProxyFactory {

    private AdvisedSupport advisedSupport;

    public ProxyFactory(AdvisedSupport advisedSupport) {
        this.advisedSupport = advisedSupport;
    }

    public Object getProxy() {
        return createAopProxy().getProxy();
    }

    private AopProxy createAopProxy() {
        if (advisedSupport.isProxyTargetClass()) {
            return new Cglib2AopProxy(advisedSupport);
        }

        return new JdkDynamicAopProxy(advisedSupport);
    }

}

public class DefaultAdvisorAutoProxyCreator implements InstantiationAwareBeanPostProcessor, BeanFactoryAware {

    private DefaultListableBeanFactory beanFactory;

    @Override
    public void setBeanFactory(BeanFactory beanFactory) throws BeansException {
        this.beanFactory = (DefaultListableBeanFactory) beanFactory;
    }

    @Override
    public Object postProcessBeforeInstantiation(Class<?> beanClass, String beanName) throws BeansException {

        if (isInfrastructureClass(beanClass)) return null;

        Collection<AspectJExpressionPointcutAdvisor> advisors = beanFactory.getBeansOfType(AspectJExpressionPointcutAdvisor.class).values();

        for (AspectJExpressionPointcutAdvisor advisor : advisors) {
            ClassFilter classFilter = advisor.getPointcut().getClassFilter();
            if (!classFilter.matches(beanClass)) continue;

            AdvisedSupport advisedSupport = new AdvisedSupport();

            TargetSource targetSource = null;
            try {
                targetSource = new TargetSource(beanClass.getDeclaredConstructor().newInstance());
            } catch (Exception e) {
                e.printStackTrace();
            }
            advisedSupport.setTargetSource(targetSource);
            advisedSupport.setMethodInterceptor((MethodInterceptor) advisor.getAdvice());
            advisedSupport.setMethodMatcher(advisor.getPointcut().getMethodMatcher());
            advisedSupport.setProxyTargetClass(false);

            return new ProxyFactory(advisedSupport).getProxy();

        }

        return null;
    }

    private boolean isInfrastructureClass(Class<?> beanClass) {
        return Advice.class.isAssignableFrom(beanClass) || Pointcut.class.isAssignableFrom(beanClass) || Advisor.class.isAssignableFrom(beanClass);
    }

    @Override
    public Object postProcessBeforeInitialization(Object bean, String beanName) throws BeansException {
        return bean;
    }

    @Override
    public Object postProcessAfterInitialization(Object bean, String beanName) throws BeansException {
        return bean;
    }
    
}

public class JdkDynamicAopProxy implements AopProxy, InvocationHandler {

    private final AdvisedSupport advised;

    public JdkDynamicAopProxy(AdvisedSupport advised) {
        this.advised = advised;
    }

    @Override
    public Object getProxy() {
        return Proxy.newProxyInstance(Thread.currentThread().getContextClassLoader(), advised.getTargetSource().getTargetClass(), this);
    }

    @Override
    public Object invoke(Object proxy, Method method, Object[] args) throws Throwable {
        if (advised.getMethodMatcher().matches(method, advised.getTargetSource().getTarget().getClass())) {
            MethodInterceptor methodInterceptor = advised.getMethodInterceptor();
            return methodInterceptor.invoke(new ReflectiveMethodInvocation(advised.getTargetSource().getTarget(), method, args));
        }
        return method.invoke(advised.getTargetSource().getTarget(), args);
    }

}

public class Cglib2AopProxy implements AopProxy {

    private final AdvisedSupport advised;

    public Cglib2AopProxy(AdvisedSupport advised) {
        this.advised = advised;
    }

    @Override
    public Object getProxy() {
        Enhancer enhancer = new Enhancer();
        enhancer.setSuperclass(advised.getTargetSource().getTarget().getClass());
        enhancer.setInterfaces(advised.getTargetSource().getTargetClass());
        enhancer.setCallback(new DynamicAdvisedInterceptor(advised));
        return enhancer.create();
    }

    private static class DynamicAdvisedInterceptor implements MethodInterceptor {

        private final AdvisedSupport advised;

        public DynamicAdvisedInterceptor(AdvisedSupport advised) {
            this.advised = advised;
        }

        @Override
        public Object intercept(Object o, Method method, Object[] objects, MethodProxy methodProxy) throws Throwable {
            CglibMethodInvocation methodInvocation = new CglibMethodInvocation(advised.getTargetSource().getTarget(), method, objects, methodProxy);
            if (advised.getMethodMatcher().matches(method, advised.getTargetSource().getTarget().getClass())) {
                return advised.getMethodInterceptor().invoke(methodInvocation);
            }
            return methodInvocation.proceed();
        }
    }

    private static class CglibMethodInvocation extends ReflectiveMethodInvocation {

        private final MethodProxy methodProxy;

        public CglibMethodInvocation(Object target, Method method, Object[] arguments, MethodProxy methodProxy) {
            super(target, method, arguments);
            this.methodProxy = methodProxy;
        }

        @Override
        public Object proceed() throws Throwable {
            return this.methodProxy.invoke(this.target, this.arguments);
        }

    }

}

UT

<?xml version="1.0" encoding="UTF-8"?>
<beans>

    <bean id="userService" class="springframework.bean.UserService"/>

    <bean class="springframework.aop.framework.autoproxy.DefaultAdvisorAutoProxyCreator"/>

    <bean id="beforeAdvice" class="springframework.bean.UserServiceBeforeAdvice"/>

    <bean id="methodInterceptor" class="springframework.aop.framework.adapter.MethodBeforeAdviceInterceptor">
        <property name="advice" ref="beforeAdvice"/>
    </bean>

    <bean id="pointcutAdvisor" class="springframework.aop.aspectj.AspectJExpressionPointcutAdvisor">
        <property name="expression" value="execution(* springframework.bean.IUserService.*(..))"/>
        <property name="advice" ref="methodInterceptor"/>
    </bean>

</beans>

    @Test
    public void test_aop() {
        ClassPathXmlApplicationContext applicationContext = new ClassPathXmlApplicationContext("classpath:spring2.xml");

        IUserService userService = applicationContext.getBean("userService", IUserService.class);
        System.out.println("测试结果：" + userService.queryUserInfo());
    }

 

版本V12.0 通过注解配置和包自动扫描的方式完成Bean对象的注册 

 

可以理解为通过xml生成BeanDefinition之外，通过在扫描指定路径中的类，解析类上的特定注释，将特定的类解析为BeanDefinition后，执行后续流程。

PropertyPlaceholderConfigurer类的作用是，作为BeanFactoryPostProcessor，修改benaDefiniton的定义，替换其中的属性值。

public class XmlBeanDefinitionReader extends AbstractBeanDefinitionReader {

    public XmlBeanDefinitionReader(BeanDefinitionRegistry registry) {
        super(registry);
    }

    public XmlBeanDefinitionReader(BeanDefinitionRegistry registry, ResourceLoader resourceLoader) {
        super(registry, resourceLoader);
    }

    @Override
    public void loadBeanDefinitions(Resource resource) throws BeansException {
        try {
            try (InputStream inputStream = resource.getInputStream()) {
                doLoadBeanDefinitions(inputStream);
            }
        } catch (IOException | ClassNotFoundException | DocumentException e) {
            throw new BeansException("IOException parsing XML document from " + resource, e);
        }
    }

    @Override
    public void loadBeanDefinitions(Resource... resources) throws BeansException {
        for (Resource resource : resources) {
            loadBeanDefinitions(resource);
        }
    }

    @Override
    public void loadBeanDefinitions(String location) throws BeansException {
        ResourceLoader resourceLoader = getResourceLoader();
        Resource resource = resourceLoader.getResource(location);
        loadBeanDefinitions(resource);
    }

    @Override
    public void loadBeanDefinitions(String... locations) throws BeansException {
        for (String location : locations) {
            loadBeanDefinitions(location);
        }
    }

    protected void doLoadBeanDefinitions(InputStream inputStream) throws ClassNotFoundException, DocumentException {
        SAXReader reader = new SAXReader();
        Document document = reader.read(inputStream);
        Element root = document.getRootElement();

        // 解析 context:component-scan 标签，扫描包中的类并提取相关信息，用于组装 BeanDefinition
        Element componentScan = root.element("component-scan");
        if (null != componentScan) {
            String scanPath = componentScan.attributeValue("base-package");
            if (StrUtil.isEmpty(scanPath)) {
                throw new BeansException("The value of base-package attribute can not be empty or null");
            }
            scanPackage(scanPath);
        }

        List<Element> beanList = root.elements("bean");
        for (Element bean : beanList) {

            String id = bean.attributeValue("id");
            String name = bean.attributeValue("name");
            String className = bean.attributeValue("class");
            String initMethod = bean.attributeValue("init-method");
            String destroyMethodName = bean.attributeValue("destroy-method");
            String beanScope = bean.attributeValue("scope");

            // 获取 Class，方便获取类中的名称
            Class<?> clazz = Class.forName(className);
            // 优先级 id > name
            String beanName = StrUtil.isNotEmpty(id) ? id : name;
            if (StrUtil.isEmpty(beanName)) {
                beanName = StrUtil.lowerFirst(clazz.getSimpleName());
            }

            // 定义Bean
            BeanDefinition beanDefinition = new BeanDefinition(clazz);
            beanDefinition.setInitMethodName(initMethod);
            beanDefinition.setDestroyMethodName(destroyMethodName);

            if (StrUtil.isNotEmpty(beanScope)) {
                beanDefinition.setScope(beanScope);
            }

            List<Element> propertyList = bean.elements("property");
            // 读取属性并填充
            for (Element property : propertyList) {
                // 解析标签：property
                String attrName = property.attributeValue("name");
                String attrValue = property.attributeValue("value");
                String attrRef = property.attributeValue("ref");
                // 获取属性值：引入对象、值对象
                Object value = StrUtil.isNotEmpty(attrRef) ? new BeanReference(attrRef) : attrValue;
                // 创建属性信息
                PropertyValue propertyValue = new PropertyValue(attrName, value);
                beanDefinition.getPropertyValues().addPropertyValue(propertyValue);
            }
            if (getRegistry().containsBeanDefinition(beanName)) {
                throw new BeansException("Duplicate beanName[" + beanName + "] is not allowed");
            }
            // 注册 BeanDefinition
            getRegistry().registerBeanDefinition(beanName, beanDefinition);
        }
    }

    private void scanPackage(String scanPath) {
        String[] basePackages = StrUtil.splitToArray(scanPath, ',');
        ClassPathBeanDefinitionScanner scanner = new ClassPathBeanDefinitionScanner(getRegistry());
        scanner.doScan(basePackages);
    }

}

public class ClassPathBeanDefinitionScanner extends ClassPathScanningCandidateComponentProvider {

    private BeanDefinitionRegistry registry;

    public ClassPathBeanDefinitionScanner(BeanDefinitionRegistry registry) {
        this.registry = registry;
    }

    public void doScan(String... basePackages) {
        for (String basePackage : basePackages) {
            Set<BeanDefinition> candidates = findCandidateComponents(basePackage);
            for (BeanDefinition beanDefinition : candidates) {
                // 解析 Bean 的作用域 singleton、prototype
                String beanScope = resolveBeanScope(beanDefinition);
                if (StrUtil.isNotEmpty(beanScope)) {
                    beanDefinition.setScope(beanScope);
                }
                registry.registerBeanDefinition(determineBeanName(beanDefinition), beanDefinition);
            }
        }
    }

    private String resolveBeanScope(BeanDefinition beanDefinition) {
        Class<?> beanClass = beanDefinition.getBeanClass();
        Scope scope = beanClass.getAnnotation(Scope.class);
        if (null != scope) return scope.value();
        return StrUtil.EMPTY;
    }

    private String determineBeanName(BeanDefinition beanDefinition) {
        Class<?> beanClass = beanDefinition.getBeanClass();
        Component component = beanClass.getAnnotation(Component.class);
        String value = component.value();
        if (StrUtil.isEmpty(value)) {
            value = StrUtil.lowerFirst(beanClass.getSimpleName());
        }
        return value;
    }

}

public class ClassPathScanningCandidateComponentProvider {

    public Set<BeanDefinition> findCandidateComponents(String basePackage) {
        Set<BeanDefinition> candidates = new LinkedHashSet<>();
        Set<Class<?>> classes = ClassUtil.scanPackageByAnnotation(basePackage, Component.class);
        for (Class<?> clazz : classes) {
            candidates.add(new BeanDefinition(clazz));
        }
        return candidates;
    }

}

public class PropertyPlaceholderConfigurer implements BeanFactoryPostProcessor {

    /**
     * Default placeholder prefix: {@value}
     */
    public static final String DEFAULT_PLACEHOLDER_PREFIX = "${";

    /**
     * Default placeholder suffix: {@value}
     */
    public static final String DEFAULT_PLACEHOLDER_SUFFIX = "}";

    private String location;

    @Override
    public void postProcessBeanFactory(ConfigurableListableBeanFactory beanFactory) throws BeansException {
        // 加载属性文件
        try {
            DefaultResourceLoader resourceLoader = new DefaultResourceLoader();
            Resource resource = resourceLoader.getResource(location);
            Properties properties = new Properties();
            properties.load(resource.getInputStream());

            String[] beanDefinitionNames = beanFactory.getBeanDefinitionNames();
            for (String beanName : beanDefinitionNames) {
                BeanDefinition beanDefinition = beanFactory.getBeanDefinition(beanName);

                PropertyValues propertyValues = beanDefinition.getPropertyValues();
                for (PropertyValue propertyValue : propertyValues.getPropertyValues()) {
                    Object value = propertyValue.getValue();
                    if (!(value instanceof String)) continue;
                    String strVal = (String) value;
                    StringBuilder buffer = new StringBuilder(strVal);
                    int startIdx = strVal.indexOf(DEFAULT_PLACEHOLDER_PREFIX);
                    int stopIdx = strVal.indexOf(DEFAULT_PLACEHOLDER_SUFFIX);
                    if (startIdx != -1 && stopIdx != -1 && startIdx < stopIdx) {
                        String propKey = strVal.substring(startIdx + 2, stopIdx);
                        String propVal = properties.getProperty(propKey);
                        buffer.replace(startIdx, stopIdx + 1, propVal);
                        propertyValues.addPropertyValue(new PropertyValue(propertyValue.getName(), buffer.toString()));
                    }
                }
            }
        } catch (IOException e) {
            throw new BeansException("Could not load properties", e);
        }
    }

    public void setLocation(String location) {
        this.location = location;
    }

}

UT

<?xml version="1.0" encoding="UTF-8"?>
<beans xmlns="http://www.springframework.org/schema/beans"
       xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
       xmlns:context="http://www.springframework.org/schema/context"
       xsi:schemaLocation="http://www.springframework.org/schema/beans
             http://www.springframework.org/schema/beans/spring-beans.xsd
         http://www.springframework.org/schema/context">

    <bean class="springframework.beans.factory.PropertyPlaceholderConfigurer">
        <property name="location" value="classpath:token.properties"/>
    </bean>

    <bean id="userService" class="springframework.bean.UserService">
        <property name="token" value="${token}"/>
    </bean>

</beans>

<?xml version="1.0" encoding="UTF-8"?>
<beans xmlns="http://www.springframework.org/schema/beans"
       xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
       xmlns:context="http://www.springframework.org/schema/context"
       xsi:schemaLocation="http://www.springframework.org/schema/beans
             http://www.springframework.org/schema/beans/spring-beans.xsd
         http://www.springframework.org/schema/context">

    <context:component-scan base-package="springframework.bean"/>

</beans>

 @Test
    public void test_scan() {
        ClassPathXmlApplicationContext applicationContext = new ClassPathXmlApplicationContext("classpath:spring-scan.xml");
        IUserService userService = applicationContext.getBean("userService", IUserService.class);
        System.out.println("测试结果：" + userService.queryUserInfo());
    }

    @Test
    public void test_property() {
        ClassPathXmlApplicationContext applicationContext = new ClassPathXmlApplicationContext("classpath:spring-property.xml");
        IUserService userService = applicationContext.getBean("userService", IUserService.class);
        System.out.println("测试结果：" + userService);
    }

@Component("userService")
public class UserService implements IUserService {

    private String token;

    public String queryUserInfo() {
        try {
            Thread.sleep(new Random(1).nextInt(100));
        } catch (InterruptedException e) {
            e.printStackTrace();
        }
        return "a，b，c";
    }

    public String register(String userName) {
        try {
            Thread.sleep(new Random(1).nextInt(100));
        } catch (InterruptedException e) {
            e.printStackTrace();
        }
        return "注册用户：" + userName + " success！";
    }

    @Override
    public String toString() {
        return "UserService#token = { " + token + " }";
    }

    public String getToken() {
        return token;
    }

    public void setToken(String token) {
        this.token = token;
    }
}

 

 

版本V13.0 通过注解给属性注入配置和Bean对象 

 

 

实现原理 在AbstractAutowireCapableBeanFactory的createBean方法中 在设置 Bean 属性之前，允许 BeanPostProcessor 修改属性值。

InstantiationAwareBeanPostProcessor中解析@Value,@Autowire, 而@Value的解析参考V10中的PropertyPlaceholderConfigurer

 

public abstract class AbstractAutowireCapableBeanFactory extends AbstractBeanFactory implements AutowireCapableBeanFactory {

    private InstantiationStrategy instantiationStrategy = new CglibSubclassingInstantiationStrategy();

    @Override
    protected Object createBean(String beanName, BeanDefinition beanDefinition, Object[] args) throws BeansException {
        Object bean = null;
        try {
            // 判断是否返回代理 Bean 对象
            bean = resolveBeforeInstantiation(beanName, beanDefinition);
            if (null != bean) {
                return bean;
            }
            // 实例化 Bean
            bean = createBeanInstance(beanDefinition, beanName, args);

            // 在设置 Bean 属性之前，允许 BeanPostProcessor 修改属性值
            applyBeanPostProcessorsBeforeApplyingPropertyValues(beanName, bean, beanDefinition);

            // 给 Bean 填充属性
            applyPropertyValues(beanName, bean, beanDefinition);
            // 执行 Bean 的初始化方法和 BeanPostProcessor 的前置和后置处理方法
            bean = initializeBean(beanName, bean, beanDefinition);
        } catch (Exception e) {
            throw new BeansException("Instantiation of bean failed", e);
        }

        // 注册实现了 DisposableBean 接口的 Bean 对象
        registerDisposableBeanIfNecessary(beanName, bean, beanDefinition);

        // 判断 SCOPE_SINGLETON、SCOPE_PROTOTYPE
        if (beanDefinition.isSingleton()) {
            registerSingleton(beanName, bean);
        }
        return bean;
    }

    /**
     * 在设置 Bean 属性之前，允许 BeanPostProcessor 修改属性值
     *
     * @param beanName
     * @param bean
     * @param beanDefinition
     */
    protected void applyBeanPostProcessorsBeforeApplyingPropertyValues(String beanName, Object bean, BeanDefinition beanDefinition) {
        for (BeanPostProcessor beanPostProcessor : getBeanPostProcessors()) {
            if (beanPostProcessor instanceof InstantiationAwareBeanPostProcessor){
                PropertyValues pvs = ((InstantiationAwareBeanPostProcessor) beanPostProcessor).postProcessPropertyValues(beanDefinition.getPropertyValues(), bean, beanName);
                if (null != pvs) {
                    for (PropertyValue propertyValue : pvs.getPropertyValues()) {
                        beanDefinition.getPropertyValues().addPropertyValue(propertyValue);
                    }
                }
            }
        }
    }
    protected Object resolveBeforeInstantiation(String beanName, BeanDefinition beanDefinition) {
        Object bean = applyBeanPostProcessorsBeforeInstantiation(beanDefinition.getBeanClass(), beanName);
        if (null != bean) {
            bean = applyBeanPostProcessorsAfterInitialization(bean, beanName);
        }
        return bean;
    }

    protected Object applyBeanPostProcessorsBeforeInstantiation(Class<?> beanClass, String beanName) {
        for (BeanPostProcessor beanPostProcessor : getBeanPostProcessors()) {
            if (beanPostProcessor instanceof InstantiationAwareBeanPostProcessor) {
                Object result = ((InstantiationAwareBeanPostProcessor) beanPostProcessor).postProcessBeforeInstantiation(beanClass, beanName);
                if (null != result) return result;
            }
        }
        return null;
    }

    protected void registerDisposableBeanIfNecessary(String beanName, Object bean, BeanDefinition beanDefinition) {
        // 非 Singleton 类型的 Bean 不执行销毁方法
        if (!beanDefinition.isSingleton()) return;

        if (bean instanceof DisposableBean || StrUtil.isNotEmpty(beanDefinition.getDestroyMethodName())) {
            registerDisposableBean(beanName, new DisposableBeanAdapter(bean, beanName, beanDefinition));
        }
    }

    protected Object createBeanInstance(BeanDefinition beanDefinition, String beanName, Object[] args) {
        Constructor constructorToUse = null;
        Class<?> beanClass = beanDefinition.getBeanClass();
        Constructor<?>[] declaredConstructors = beanClass.getDeclaredConstructors();
        for (Constructor ctor : declaredConstructors) {
            if (null != args && ctor.getParameterTypes().length == args.length) {
                constructorToUse = ctor;
                break;
            }
        }
        return getInstantiationStrategy().instantiate(beanDefinition, beanName, constructorToUse, args);
    }

    /**
     * Bean 属性填充
     */
    protected void applyPropertyValues(String beanName, Object bean, BeanDefinition beanDefinition) {
        try {
            PropertyValues propertyValues = beanDefinition.getPropertyValues();
            for (PropertyValue propertyValue : propertyValues.getPropertyValues()) {

                String name = propertyValue.getName();
                Object value = propertyValue.getValue();

                if (value instanceof BeanReference) {
                    // A 依赖 B，获取 B 的实例化
                    BeanReference beanReference = (BeanReference) value;
                    value = getBean(beanReference.getBeanName());
                }
                // 属性填充
                BeanUtil.setFieldValue(bean, name, value);
            }
        } catch (Exception e) {
            throw new BeansException("Error setting property values：" + beanName);
        }
    }

    public InstantiationStrategy getInstantiationStrategy() {
        return instantiationStrategy;
    }

    public void setInstantiationStrategy(InstantiationStrategy instantiationStrategy) {
        this.instantiationStrategy = instantiationStrategy;
    }

    private Object initializeBean(String beanName, Object bean, BeanDefinition beanDefinition) {

        // invokeAwareMethods
        if (bean instanceof Aware) {
            if (bean instanceof BeanFactoryAware) {
                ((BeanFactoryAware) bean).setBeanFactory(this);
            }
            if (bean instanceof BeanClassLoaderAware) {
                ((BeanClassLoaderAware) bean).setBeanClassLoader(getBeanClassLoader());
            }
            if (bean instanceof BeanNameAware) {
                ((BeanNameAware) bean).setBeanName(beanName);
            }
        }

        // 1. 执行 BeanPostProcessor Before 处理
        Object wrappedBean = applyBeanPostProcessorsBeforeInitialization(bean, beanName);

        // 执行 Bean 对象的初始化方法
        try {
            invokeInitMethods(beanName, wrappedBean, beanDefinition);
        } catch (Exception e) {
            throw new BeansException("Invocation of init method of bean[" + beanName + "] failed", e);
        }

        // 2. 执行 BeanPostProcessor After 处理
        wrappedBean = applyBeanPostProcessorsAfterInitialization(wrappedBean, beanName);
        return wrappedBean;
    }

    private void invokeInitMethods(String beanName, Object bean, BeanDefinition beanDefinition) throws Exception {
        // 1. 实现接口 InitializingBean
        if (bean instanceof InitializingBean) {
            ((InitializingBean) bean).afterPropertiesSet();
        }

        // 2. 注解配置 init-method {判断是为了避免二次执行销毁}
        String initMethodName = beanDefinition.getInitMethodName();
        if (StrUtil.isNotEmpty(initMethodName)) {
            Method initMethod = beanDefinition.getBeanClass().getMethod(initMethodName);
            if (null == initMethod) {
                throw new BeansException("Could not find an init method named '" + initMethodName + "' on bean with name '" + beanName + "'");
            }
            initMethod.invoke(bean);
        }
    }

    @Override
    public Object applyBeanPostProcessorsBeforeInitialization(Object existingBean, String beanName) throws BeansException {
        Object result = existingBean;
        for (BeanPostProcessor processor : getBeanPostProcessors()) {
            Object current = processor.postProcessBeforeInitialization(result, beanName);
            if (null == current) return result;
            result = current;
        }
        return result;
    }

    @Override
    public Object applyBeanPostProcessorsAfterInitialization(Object existingBean, String beanName) throws BeansException {
        Object result = existingBean;
        for (BeanPostProcessor processor : getBeanPostProcessors()) {
            Object current = processor.postProcessAfterInitialization(result, beanName);
            if (null == current) return result;
            result = current;
        }
        return result;
    }

}

public interface InstantiationAwareBeanPostProcessor extends BeanPostProcessor {

    /**
     * Apply this BeanPostProcessor <i>before the target bean gets instantiated</i>.
     * The returned bean object may be a proxy to use instead of the target bean,
     * effectively suppressing default instantiation of the target bean.
     * <p>
     * 在 Bean 对象执行初始化方法之前，执行此方法
     *
     * @param beanClass
     * @param beanName
     * @return
     * @throws BeansException
     */
    Object postProcessBeforeInstantiation(Class<?> beanClass, String beanName) throws BeansException;

    PropertyValues postProcessPropertyValues(PropertyValues pvs, Object bean, String beanName);
}

public class AutowiredAnnotationBeanPostProcessor implements InstantiationAwareBeanPostProcessor, BeanFactoryAware {

    private ConfigurableListableBeanFactory beanFactory;

    @Override
    public void setBeanFactory(BeanFactory beanFactory) throws BeansException {
        this.beanFactory = (ConfigurableListableBeanFactory) beanFactory;
    }

    @Override
    public PropertyValues postProcessPropertyValues(PropertyValues pvs, Object bean, String beanName) throws BeansException {
        // 1. 处理注解 @Value
        Class<?> clazz = bean.getClass();
        clazz = ClassUtils.isCglibProxyClass(clazz) ? clazz.getSuperclass() : clazz;

        Field[] declaredFields = clazz.getDeclaredFields();

        for (Field field : declaredFields) {
            Value valueAnnotation = field.getAnnotation(Value.class);
            if (null != valueAnnotation) {
                String value = valueAnnotation.value();
                value = beanFactory.resolveEmbeddedValue(value);
                BeanUtil.setFieldValue(bean, field.getName(), value);
            }
        }

        // 2. 处理注解 @Autowired
        for (Field field : declaredFields) {
            Autowired autowiredAnnotation = field.getAnnotation(Autowired.class);
            if (null != autowiredAnnotation) {
                Class<?> fieldType = field.getType();
                String dependentBeanName = null;
                Qualifier qualifierAnnotation = field.getAnnotation(Qualifier.class);
                Object dependentBean = null;
                if (null != qualifierAnnotation) {
                    dependentBeanName = qualifierAnnotation.value();
                    dependentBean = beanFactory.getBean(dependentBeanName, fieldType);
                } else {
                    dependentBean = beanFactory.getBean(fieldType);
                }
                BeanUtil.setFieldValue(bean, field.getName(), dependentBean);
            }
        }

        return pvs;
    }

    @Override
    public Object postProcessBeforeInstantiation(Class<?> beanClass, String beanName) throws BeansException {
        return null;
    }

    @Override
    public Object postProcessBeforeInitialization(Object bean, String beanName) throws BeansException {
        return null;
    }

    @Override
    public Object postProcessAfterInitialization(Object bean, String beanName) throws BeansException {
        return null;
    }
}

public class PropertyPlaceholderConfigurer implements BeanFactoryPostProcessor {

    /**
     * Default placeholder prefix: {@value}
     */
    public static final String DEFAULT_PLACEHOLDER_PREFIX = "${";

    /**
     * Default placeholder suffix: {@value}
     */
    public static final String DEFAULT_PLACEHOLDER_SUFFIX = "}";

    private String location;

    @Override
    public void postProcessBeanFactory(ConfigurableListableBeanFactory beanFactory) throws BeansException {
        // 加载属性文件
        try {
            DefaultResourceLoader resourceLoader = new DefaultResourceLoader();
            Resource resource = resourceLoader.getResource(location);
            Properties properties = new Properties();
            properties.load(resource.getInputStream());

            String[] beanDefinitionNames = beanFactory.getBeanDefinitionNames();
            for (String beanName : beanDefinitionNames) {
                BeanDefinition beanDefinition = beanFactory.getBeanDefinition(beanName);

                PropertyValues propertyValues = beanDefinition.getPropertyValues();
                for (PropertyValue propertyValue : propertyValues.getPropertyValues()) {
                    Object value = propertyValue.getValue();
                    if (!(value instanceof String)) continue;
                    String strVal = (String) value;
                    StringBuilder buffer = new StringBuilder(strVal);
                    int startIdx = strVal.indexOf(DEFAULT_PLACEHOLDER_PREFIX);
                    int stopIdx = strVal.indexOf(DEFAULT_PLACEHOLDER_SUFFIX);
                    if (startIdx != -1 && stopIdx != -1 && startIdx < stopIdx) {
                        String propKey = strVal.substring(startIdx + 2, stopIdx);
                        String propVal = properties.getProperty(propKey);
                        buffer.replace(startIdx, stopIdx + 1, propVal);
                        propertyValues.addPropertyValue(new PropertyValue(propertyValue.getName(), buffer.toString()));
                    }
                }

                // 向容器中添加字符串解析器，供解析@Value注解使用
                StringValueResolver valueResolver = new PlaceholderResolvingStringValueResolver(properties);
                beanFactory.addEmbeddedValueResolver(valueResolver);

            }
        } catch (IOException e) {
            throw new BeansException("Could not load properties", e);
        }
    }

    public void setLocation(String location) {
        this.location = location;
    }


    private String resolvePlaceholder(String value, Properties properties) {
        String strVal = value;
        StringBuilder buffer = new StringBuilder(strVal);
        int startIdx = strVal.indexOf(DEFAULT_PLACEHOLDER_PREFIX);
        int stopIdx = strVal.indexOf(DEFAULT_PLACEHOLDER_SUFFIX);
        if (startIdx != -1 && stopIdx != -1 && startIdx < stopIdx) {
            String propKey = strVal.substring(startIdx + 2, stopIdx);
            String propVal = properties.getProperty(propKey);
            buffer.replace(startIdx, stopIdx + 1, propVal);
        }
        return buffer.toString();
    }

    private class PlaceholderResolvingStringValueResolver implements StringValueResolver {

        private final Properties properties;

        public PlaceholderResolvingStringValueResolver(Properties properties) {
            this.properties = properties;
        }

        @Override
        public String resolveStringValue(String strVal) {
            return PropertyPlaceholderConfigurer.this.resolvePlaceholder(strVal, properties);
        }
    }

}

public interface ConfigurableBeanFactory extends HierarchicalBeanFactory, SingletonBeanRegistry {

    String SCOPE_SINGLETON = "singleton";

    String SCOPE_PROTOTYPE = "prototype";

    void addBeanPostProcessor(BeanPostProcessor beanPostProcessor);

    /**
     * 销毁单例对象
     */
    void destroySingletons();

    /**
     * Resolve the given embedded value, e.g. an annotation attribute.
     * @param value the value to resolve
     * @return the resolved value (may be the original value as-is)
     * @since 3.0
     */
    String resolveEmbeddedValue(String value);

    void addEmbeddedValueResolver(StringValueResolver valueResolver);
}

UT

@Component("userService")
public class UserService implements IUserService {

    @Value("${token}")
    private String token;

    @Autowired
    private UserDao userDao;

    public String queryUserInfo() {
        try {
            Thread.sleep(new Random(1).nextInt(100));
        } catch (InterruptedException e) {
            e.printStackTrace();
        }
        return userDao.queryUserName("10001") + "，" + token;
    }

    public String register(String userName) {
        try {
            Thread.sleep(new Random(1).nextInt(100));
        } catch (InterruptedException e) {
            e.printStackTrace();
        }
        return "注册用户：" + userName + " success！";
    }

    @Override
    public String toString() {
        return "UserService#token = { " + token + " }";
    }

    public String getToken() {
        return token;
    }

    public void setToken(String token) {
        this.token = token;
    }

    public UserDao getUserDao() {
        return userDao;
    }

    public void setUserDao(UserDao userDao) {
        this.userDao = userDao;
    }
}

<?xml version="1.0" encoding="UTF-8"?>
<beans xmlns="http://www.springframework.org/schema/beans"
       xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
       xmlns:context="http://www.springframework.org/schema/context"
       xsi:schemaLocation="http://www.springframework.org/schema/beans
             http://www.springframework.org/schema/beans/spring-beans.xsd
         http://www.springframework.org/schema/context">

    <bean class="springframework.beans.factory.PropertyPlaceholderConfigurer">
        <property name="location" value="classpath:token.properties"/>
    </bean>

    <context:component-scan base-package="springframework.bean"/>

</beans>

 

 

版本V14.0 给代理对象的属性设置值

在V13版本中，是在 InstantiationAwareBeanPostProcessor.postProcessBeforeInstantiation中实现的，在对象实例化之前进行代理对象的生成，但是这样会造成提前返回，而错过属性值的赋值。 所以现在将代理逻辑由 InstantiationAwareBeanPostProcessor.postProcessBeforeInstantiation迁移到DefaultAdvisorAutoProxyCreator.postProcessAfterInitialization。

其中可能会遇到因为代理而遇到的各种问题。这里将实例化策略更换为SimpleInstantiationStrategy，并且将代理实现逻辑更为JdkDynamicAopProxy。

 参考：

https://github.com/DerekYRC/mini-spring/blob/main/changelog.md#bug-fix%E6%B2%A1%E6%9C%89%E4%B8%BA%E4%BB%A3%E7%90%86bean%E8%AE%BE%E7%BD%AE%E5%B1%9E%E6%80%A7discovered-and-fixed-by-kerwin89

ps:自己定位问题才是理解这套框架最佳的学习方式。

版本V15.0 通过三级缓存解决循环依赖

1简单版本的循环依赖问题 ，不存在代理对象的循环依赖

public class A {
    public B getB() {
        return b;
    }

    public void setB(B b) {
        this.b = b;
    }

    private B b;

}

public class B {

    public A getA() {
        return a;
    }

    public void setA(A a) {
        this.a = a;
    }

    private A a;
}

<?xml version="1.0" encoding="UTF-8"?>
<beans xmlns="http://www.springframework.org/schema/beans"
       xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
       xsi:schemaLocation="http://www.springframework.org/schema/beans
             http://www.springframework.org/schema/beans/spring-beans.xsd">

    <bean id="A" class="springframework.bean.A">
        <property name="b" ref="B"/>
    </bean>

    <bean id="B" class="springframework.bean.B">
        <property name="a" ref="A"/>
    </bean>

</beans>

由于在getBean(A) 中需要 getBean(B)，getBean(B）中又需要 getBean(A)，死循环会造成栈溢出。 

仔细分析原因是由于我们在AbstractBeanFactory getSingleton(beanName) 与在AbstractAutowireCapableBeanFactory registerSingleton(beanName, exposedObject)的时机问题。

当前我们是在bean实例化并初始化后才会将单例注册进singletonObjects，如果在bean实例化后，就提前注入到singletonObjects。这样就能避免简单的循环依赖，为了将初始化并给属性值赋值后的bean与仅完成实例化的bean区分来，我们将后者放入earlySingletonObjects。 getSingleton时先尝试获取singletonObjects中的bean，如果没有的话在尝试从earlySingletonObjects获取bean。

public abstract class AbstractAutowireCapableBeanFactory extends AbstractBeanFactory implements AutowireCapableBeanFactory {

    private InstantiationStrategy instantiationStrategy = new SimpleInstantiationStrategy();

    @Override
    protected Object createBean(String beanName, BeanDefinition beanDefinition, Object[] args) throws BeansException {
        // 判断是否返回代理 Bean 对象
        Object bean = resolveBeforeInstantiation(beanName, beanDefinition);
        if (null != bean) {
            return bean;
        }

        return doCreateBean(beanName, beanDefinition, args);
    }

    protected Object doCreateBean(String beanName, BeanDefinition beanDefinition, Object[] args) throws BeansException {
        Object bean = null;
        try {
            // 实例化 Bean
            bean = createBeanInstance(beanDefinition, beanName, args);
            if (beanDefinition.isSingleton()) {
                // 二级缓存
                registerEarlySingleton(beanName, bean);
            }
            // 实例化后判断
            boolean continueWithPropertyPopulation = applyBeanPostProcessorsAfterInstantiation(beanName, bean);
            if (!continueWithPropertyPopulation) {
                return bean;
            }

            // 在设置 Bean 属性之前，允许 BeanPostProcessor 修改属性值
            applyBeanPostProcessorsBeforeApplyingPropertyValues(beanName, bean, beanDefinition);

            // 给 Bean 填充属性
            applyPropertyValues(beanName, bean, beanDefinition);
            // 执行 Bean 的初始化方法和 BeanPostProcessor 的前置和后置处理方法
            bean = initializeBean(beanName, bean, beanDefinition);
        } catch (Exception e) {
            throw new BeansException("Instantiation of bean failed", e);
        }

        // 注册实现了 DisposableBean 接口的 Bean 对象
        registerDisposableBeanIfNecessary(beanName, bean, beanDefinition);

        // 判断 SCOPE_SINGLETON、SCOPE_PROTOTYPE
        Object exposedObject = bean;
        if (beanDefinition.isSingleton()) {
            // registerSingleton(beanName, bean);

            // 获取代理对象
           // exposedObject = getSingleton(beanName);
            registerSingleton(beanName, exposedObject);
        }
        return bean;
    }}

public class DefaultSingletonBeanRegistry implements SingletonBeanRegistry {

    /**
     * Internal marker for a null singleton object:
     * used as marker value for concurrent Maps (which don't support null values).
     */
    protected static final Object NULL_OBJECT = new Object();


    private final Map<String, DisposableBean> disposableBeans = new HashMap<>();





    // 一级缓存，普通对象
    /**
     * Cache of singleton objects: bean name --> bean instance
     */
    private Map<String, Object> singletonObjects = new ConcurrentHashMap<>();

    // 二级缓存，提前暴漏对象，没有完全实例化的对象
    /**
     * Cache of early singleton objects: bean name --> bean instance
     */
    protected final Map<String, Object> earlySingletonObjects = new HashMap<String, Object>();

    // 三级缓存，存放代理对象
    /**
     * Cache of singleton factories: bean name --> ObjectFactory
     */
    private final Map<String, ObjectFactory<?>> singletonFactories = new HashMap<String, ObjectFactory<?>>();

    @Override
    public Object getSingleton(String beanName) {
        Object singletonObject = singletonObjects.get(beanName);
        if (singletonObject != null) {
            return singletonObject;
        }
        return earlySingletonObjects.get(beanName);
    }

    public void registerEarlySingleton(String beanName, Object singletonObject) {
        earlySingletonObjects.put(beanName, singletonObject);
    }
    @Override
    public void registerSingleton(String beanName, Object singletonObject) {
        singletonObjects.put(beanName, singletonObject);
    }


    public void registerDisposableBean(String beanName, DisposableBean bean) {
        disposableBeans.put(beanName, bean);
    }

    public void destroySingletons() {
        Set<String> keySet = this.disposableBeans.keySet();
        Object[] disposableBeanNames = keySet.toArray();

        for (int i = disposableBeanNames.length - 1; i >= 0; i--) {
            Object beanName = disposableBeanNames[i];
            DisposableBean disposableBean = disposableBeans.remove(beanName);
            try {
                disposableBean.destroy();
            } catch (Exception e) {
                throw new BeansException("Destroy method on bean with name '" + beanName + "' threw an exception", e);
            }
        }
    }


}

这样简单循环依赖解决了。

 

 2.【解决有代理对象时的循环依赖问题，需要提前暴露代理对象的引用，而不是暴露实例化后的bean的引用（这是上节的遗留问题的原因，应该提前暴露A的代理对象的引用）。

spring中用singletonFactories（一般称第三级缓存）解决有代理对象时的循环依赖问题。在实例化后提前暴露代理对象的引用（见AbstractAutowireCapableBeanFactory#doCreateBean方法第6行）。

getBean()时依次检查一级缓存singletonObjects、二级缓存earlySingletonObjects和三级缓存singletonFactories中是否包含该bean。如果三级缓存中包含该bean，则挪至二级缓存中，然后直接返回该bean。见AbstractBeanFactory#getBean方法第1行。

最后将代理bean放进一级缓存singletonObjects，见AbstractAutowireCapableBeanFactory第104行】 

public abstract class AbstractAutowireCapableBeanFactory extends AbstractBeanFactory
        implements AutowireCapableBeanFactory {

    private InstantiationStrategy instantiationStrategy = new SimpleInstantiationStrategy();

    @Override
    protected Object createBean(String beanName, BeanDefinition beanDefinition) throws BeansException {
        //如果bean需要代理，则直接返回代理对象
        Object bean = resolveBeforeInstantiation(beanName, beanDefinition);
        if (bean != null) {
            return bean;
        }

        return doCreateBean(beanName, beanDefinition);
    }

    /**
     * 执行InstantiationAwareBeanPostProcessor的方法，如果bean需要代理，直接返回代理对象
     *
     * @param beanName
     * @param beanDefinition
     * @return
     */
    protected Object resolveBeforeInstantiation(String beanName, BeanDefinition beanDefinition) {
        Object bean = applyBeanPostProcessorsBeforeInstantiation(beanDefinition.getBeanClass(), beanName);
        if (bean != null) {
            bean = applyBeanPostProcessorsAfterInitialization(bean, beanName);
        }
        return bean;
    }

    protected Object applyBeanPostProcessorsBeforeInstantiation(Class beanClass, String beanName) {
        for (BeanPostProcessor beanPostProcessor : getBeanPostProcessors()) {
            if (beanPostProcessor instanceof InstantiationAwareBeanPostProcessor) {
                Object result = ((InstantiationAwareBeanPostProcessor) beanPostProcessor).postProcessBeforeInstantiation(beanClass, beanName);
                if (result != null) {
                    return result;
                }
            }
        }

        return null;
    }

    protected Object doCreateBean(String beanName, BeanDefinition beanDefinition) {
        Object bean;
        try {
            bean = createBeanInstance(beanDefinition);

            //为解决循环依赖问题，将实例化后的bean放进缓存中提前暴露
            if (beanDefinition.isSingleton()) {
                Object finalBean = bean;
                addSingletonFactory(beanName, new ObjectFactory<Object>() {
                    @Override
                    public Object getObject() throws BeansException {
                        return getEarlyBeanReference(beanName, beanDefinition, finalBean);
                    }
                });
            }

            //实例化bean之后执行
            boolean continueWithPropertyPopulation = applyBeanPostProcessorsAfterInstantiation(beanName, bean);
            if (!continueWithPropertyPopulation) {
                return bean;
            }
            //在设置bean属性之前，允许BeanPostProcessor修改属性值
            applyBeanPostProcessorsBeforeApplyingPropertyValues(beanName, bean, beanDefinition);
            //为bean填充属性
            applyPropertyValues(beanName, bean, beanDefinition);
            //执行bean的初始化方法和BeanPostProcessor的前置和后置处理方法
            bean = initializeBean(beanName, bean, beanDefinition);
        } catch (Exception e) {
            throw new BeansException("Instantiation of bean failed", e);
        }

        //注册有销毁方法的bean
        registerDisposableBeanIfNecessary(beanName, bean, beanDefinition);

        Object exposedObject = bean;
        if (beanDefinition.isSingleton()) {
            //如果有代理对象，此处获取代理对象
            exposedObject = getSingleton(beanName);
            addSingleton(beanName, exposedObject);
        }
        return exposedObject;
    }

    protected Object getEarlyBeanReference(String beanName, BeanDefinition beanDefinition, Object bean) {
        Object exposedObject = bean;
        for (BeanPostProcessor bp : getBeanPostProcessors()) {
            if (bp instanceof InstantiationAwareBeanPostProcessor) {
                exposedObject = ((InstantiationAwareBeanPostProcessor) bp).getEarlyBeanReference(exposedObject, beanName);
                if (exposedObject == null) {
                    return exposedObject;
                }
            }
        }

        return exposedObject;
    }

public class DefaultAdvisorAutoProxyCreator implements InstantiationAwareBeanPostProcessor, BeanFactoryAware {

    private DefaultListableBeanFactory beanFactory;

    private Set<Object> earlyProxyReferences = new HashSet<>();

    @Override
    public Object postProcessAfterInitialization(Object bean, String beanName) throws BeansException {
        if (!earlyProxyReferences.contains(beanName)) {
            return wrapIfNecessary(bean, beanName);
        }

        return bean;
    }

    @Override
    public Object getEarlyBeanReference(Object bean, String beanName) throws BeansException {
        earlyProxyReferences.add(beanName);
        return wrapIfNecessary(bean, beanName);
    }

    protected Object wrapIfNecessary(Object bean, String beanName) {
        //避免死循环
        if (isInfrastructureClass(bean.getClass())) {
            return bean;
        }

        Collection<AspectJExpressionPointcutAdvisor> advisors = beanFactory.getBeansOfType(AspectJExpressionPointcutAdvisor.class).values();
        try {
            for (AspectJExpressionPointcutAdvisor advisor : advisors) {
                ClassFilter classFilter = advisor.getPointcut().getClassFilter();
                if (classFilter.matches(bean.getClass())) {
                    AdvisedSupport advisedSupport = new AdvisedSupport();
                    TargetSource targetSource = new TargetSource(bean);

                    advisedSupport.setTargetSource(targetSource);
                    advisedSupport.setMethodInterceptor((MethodInterceptor) advisor.getAdvice());
                    advisedSupport.setMethodMatcher(advisor.getPointcut().getMethodMatcher());

                    //返回代理对象
                    return new ProxyFactory(advisedSupport).getProxy();
                }
            }
        } catch (Exception ex) {
            throw new BeansException("Error create proxy bean for: " + beanName, ex);
        }
        return bean;
    }

    private boolean isInfrastructureClass(Class<?> beanClass) {
        return Advice.class.isAssignableFrom(beanClass)
                || Pointcut.class.isAssignableFrom(beanClass)
                || Advisor.class.isAssignableFrom(beanClass);
    }

    @Override
    public void setBeanFactory(BeanFactory beanFactory) throws BeansException {
        this.beanFactory = (DefaultListableBeanFactory) beanFactory;
    }

    @Override
    public Object postProcessBeforeInstantiation(Class<?> beanClass, String beanName) throws BeansException {
        return null;
    }

    @Override
    public boolean postProcessAfterInstantiation(Object bean, String beanName) throws BeansException {
        return true;
    }

    @Override
    public Object postProcessBeforeInitialization(Object bean, String beanName) throws BeansException {
        return bean;
    }

    @Override
    public PropertyValues postProcessPropertyValues(PropertyValues pvs, Object bean, String beanName) throws BeansException {
        return pvs;
    }
}

public class DefaultSingletonBeanRegistry implements SingletonBeanRegistry {

    //一级缓存
    private Map<String, Object> singletonObjects = new HashMap<>();

    //二级缓存
    private Map<String, Object> earlySingletonObjects = new HashMap<>();

    //三级缓存
    private Map<String, ObjectFactory<?>> singletonFactories = new HashMap<String, ObjectFactory<?>>();

    private final Map<String, DisposableBean> disposableBeans = new HashMap<>();

    @Override
    public Object getSingleton(String beanName) {
        Object singletonObject = singletonObjects.get(beanName);
        if (singletonObject == null) {
            singletonObject = earlySingletonObjects.get(beanName);
            if (singletonObject == null) {
                ObjectFactory<?> singletonFactory = singletonFactories.get(beanName);
                if (singletonFactory != null) {
                    singletonObject = singletonFactory.getObject();
                    //从三级缓存放进二级缓存
                    earlySingletonObjects.put(beanName, singletonObject);
                    singletonFactories.remove(beanName);
                }
            }
        }
        return singletonObject;
    }

    @Override
    public void addSingleton(String beanName, Object singletonObject) {
        singletonObjects.put(beanName, singletonObject);
        earlySingletonObjects.remove(beanName);
        singletonFactories.remove(beanName);
    }

    protected void addSingletonFactory(String beanName, ObjectFactory<?> singletonFactory) {
        singletonFactories.put(beanName, singletonFactory);
    }

    public void registerDisposableBean(String beanName, DisposableBean bean) {
        disposableBeans.put(beanName, bean);
    }

    public void destroySingletons() {
        Set<String> beanNames = disposableBeans.keySet();
        for (String beanName : beanNames) {
            DisposableBean disposableBean = disposableBeans.remove(beanName);
            try {
                disposableBean.destroy();
            } catch (Exception e) {
                throw new BeansException("Destroy method on bean with name '" + beanName + "' threw an exception", e);
            }
        }
    }
}

<?xml version="1.0" encoding="UTF-8"?>
<beans xmlns="http://www.springframework.org/schema/beans"
       xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
       xmlns:context="http://www.springframework.org/schema/context"
       xsi:schemaLocation="http://www.springframework.org/schema/beans
             http://www.springframework.org/schema/beans/spring-beans.xsd
         http://www.springframework.org/schema/context
         http://www.springframework.org/schema/context/spring-context-4.0.xsd">

    <bean id="b" class="org.springframework.test.bean.B">
        <property name="a" ref="a"/>
    </bean>

    <!-- a被代理 -->
    <bean id="a" class="org.springframework.test.bean.A">
        <property name="b" ref="b"/>
    </bean>

    <bean class="org.springframework.aop.framework.autoproxy.DefaultAdvisorAutoProxyCreator"/>

    <bean id="pointcutAdvisor" class="org.springframework.aop.aspectj.AspectJExpressionPointcutAdvisor">
        <property name="expression" value="execution(* org.springframework.test.bean.A.func(..))"/>
        <property name="advice" ref="methodInterceptor"/>
    </bean>


    <bean id="methodInterceptor" class="org.springframework.aop.framework.adapter.MethodBeforeAdviceInterceptor">
        <property name="advice" ref="beforeAdvice"/>
    </bean>

    <bean id="beforeAdvice" class="org.springframework.test.common.ABeforeAdvice"/>

</beans>

此时 A对象会被代理，所以B对象中的A引用也应该是代理对象。

 

 

完结，撒花🎉🎉🎉🎉