Spring中创建对象的方式整理
在没有使用Spring时，开发者创建对象一般都是使用new/反射创建对象；Spring出来后简化了开发方式，它提供了一个IoC容器的实现，用于帮助开发者以依赖注入的方式管理对象之间的依赖关系，从而将开发者创建对象的所有权转移到IoC容器上，这使得Spring易于整合第三方模块，因此Spring更是一个分层的框架；
对于Spring创建对象的方式创建整理如下：
方式一：自定义BeanPostProcessor，生成代理对象
如实现InstantiationAwareBeanPostProcessor接口，其中InstantiationAwareBeanPostProcessor是一个BeanPostProcessor，它可用于处理bean实例创建前后的回调；
测试如下：
@Test
public void instantiationAwareBeanPostProcessorTest() {
AnnotationConfigApplicationContext context = new AnnotationConfigApplicationContext();
GenericBeanDefinition definition1 = new GenericBeanDefinition();
definition1.setBeanClass(DemoInstantiationAwareBPP.class);
context.registerBeanDefinition("demoInstantiationAwareBPP", definition1);
GenericBeanDefinition definition2 = new GenericBeanDefinition();
definition2.setBeanClass(InstantiationDemo.class);
context.registerBeanDefinition("instantiationDemo", definition2);
context.refresh();
InstantiationDemo bean = context.getBean(InstantiationDemo.class);
bean.invoke();
}
public class DemoInstantiationAwareBPP implements InstantiationAwareBeanPostProcessor {
private final static Log LOG = LogFactory.getLog(DemoInstantiationAwareBPP.class);
@Override
public Object postProcessBeforeInstantiation(Class<?> beanClass, String beanName) throws BeansException {
LOG.info("beanName:" + beanName + "执行postProcessBeforeInstantiation方法");
// 使用cglib生成代理对象
if (beanClass == InstantiationDemo.class) {
Enhancer enhancer = new Enhancer();
enhancer.setSuperclass(beanClass);
enhancer.setCallback((MethodInterceptor) (o, method, objects, methodProxy) -> {
boolean objFlag = method.getDeclaringClass().getName().equals("java.lang.Object");
if (!objFlag) {
LOG.info("执行方法" + method + "前");
Object rtn = methodProxy.invokeSuper(o, objects);
LOG.info("执行方法" + method + "后");
return rtn;
} else {
return methodProxy.invokeSuper(o, objects);
}
});
InstantiationDemo bean = (InstantiationDemo) enhancer.create();
LOG.info("创建代理对象:" + bean);
return bean;
}
return null;
}
@Override
public boolean postProcessAfterInstantiation(Object bean, String beanName) throws BeansException {
LOG.info("beanName:" + beanName + "执行postProcessAfterInstantiation方法");
return false;
}
}
public class InstantiationDemo {
private final static Log LOG = LogFactory.getLog(InstantiationDemo.class);
public void invoke() {
LOG.info(this);
LOG.info("InstantiationDemo invoke");
}
}
注：
MethodProxy#invokeSuper是退出当前interceptor的处理,进入下一个callback处理；
MethodProxy#invoke则会继续回调该方法,如果传递给invoke的obj参数出错容易造成递归调用；
方式二：通过反射创建
AbstractAutowireCapableBeanFactory#doCreateBean为真正创建bean的逻辑，该方法是最复杂的，包含了调用构造函数，给bean的属性赋值，调用bean的初始化操作以及生成代理对象；
该方法会调用AbstractAutowireCapableBeanFactory#createBeanInstance实例化对象，如下图；
AbstractAutowireCapableBeanFactory#createBeanInstance
判断Bean定义信息中的resolvedConstructorOrFactoryMethod是否缓存，因为需要根据参数确认到底使用哪个构造器，该过程比较消耗性能，所以采用缓存机制；
通过bean的后置处理器进行获取合适的构造器对象，有且只有一个有参构造或有且只有一个@Autowired注解构造；
创建对象方式
AbstractAutowireCapableBeanFactory#createBeanInstance根据@Autowried自动注入/调用无参构造器创建，进行相应的处理；
- instantiateBean 调用无参数的构造器进行创建对象；
- autowireConstructor @Autowired自动注入，调用构造器注入；
方式三：通过FactoryBean创建对象
AbstractBeanFactory#getObjectForBeanInstance
如果有实现了FactoryBean接口的实例，则从FactoryBean中获取实例；
测试如下：
@Test
public void mainTest13() {
AnnotationConfigApplicationContext context = new AnnotationConfigApplicationContext(
MainConfig10.class);
System.out.println("IOC容器创建完成...");
// 调用FactoryBean#getBean方法,入参为Bean id,得到的对象为FactoryBean#getObjectType的对象
// FactoryBean要获取工厂Bean本身,需要在id前加个&
// org.springframework.beans.factory.support.AbstractBeanFactory.getObjectForBeanInstance
Object factoryBean1 = context.getBean("demoFactoryBean");
Object factoryBean2 = context.getBean("demoFactoryBean");
System.out.println("factoryBean1==factoryBean2 :" + (factoryBean1 == factoryBean2));
System.out.println("bean的类型:" + factoryBean1.getClass());
Object factoryBean3 = context.getBean("&demoFactoryBean");
System.out.println("bean的类型:" + factoryBean3.getClass());
}
@Configuration
public class MainConfig10 {
@Bean
public DemoFactoryBean demoFactoryBean() {
return new DemoFactoryBean();
}
}
public class DemoFactoryBean implements FactoryBean<Person> {
/**
* 是否单例进行控制
* @return
*/
@Override
public boolean isSingleton() {
return true;
}
/**
* 返回对象，把对象放到容器中
* @return
* @throws Exception
*/
@Override
public Person getObject() throws Exception {
return new Person();
}
/**
* 返回对象类型
* @return
*/
@Override
public Class<?> getObjectType() {
return Person.class;
}
}
方式四：通过设置BeanDefinition属性Supplier创建对象
AbstractAutowireCapableBeanFactory#createBeanInstance
获取bean的supplier；
AbstractAutowireCapableBeanFactory#obtainFromSupplier
通过Suupplier#get方法获取实例，此时获取实例不是使用反射；
测试如下：
@Test
public void supplierTest() {
AnnotationConfigApplicationContext context = new AnnotationConfigApplicationContext();
GenericBeanDefinition definition = new GenericBeanDefinition();
definition.setBeanClass(BeanC.class);
definition.setInstanceSupplier((Supplier<BeanC>) BeanC::new);
context.registerBeanDefinition("beanC", definition);
context.refresh();
Assertions.assertNotNull(context.getBean("beanC"));
}
public class BeanC {
private final static Log LOG = LogFactory.getLog(BeanC.class);
public BeanC() {
LOG.info("BeanC constructor");
}
}
方式五：通过设置BeanDefinition属性factoryMethod创建对象
AbstractAutowireCapableBeanFactory#createBeanInstance
createBeanInstance是实例化对象的过程，如果beanDefinition设置了factoryMethod，则从设置的factoryMethod实例化，而supplier属性的优先级高于factoryMethod，即beanDefinition同时存在supplier和factoryMethod属性时，优先执行supplier的实例化逻辑；
mbd的factoryMethodName在BeanDefiniton加载时赋值的，如下：
ConfigurationClassBeanDefinitionReader#loadBeanDefinitionsForBeanMethod
factoryMethod使用方式：往beanDefinition设置factoryMethod所属类的beanName和factoryMethodName的属性；
使用factoryMethod实例化对象的解析逻辑：ConstructorResolver#instantiateUsingFactoryMethod
SimpleInstantiationStrategy最终通过对factoryBean反射调用factoryMethod；
测试如下：
beanDefinition只有factoryMethod属性
public class FactoryDemo {
private final static Log LOG = LogFactory.getLog(FactoryDemo.class);
private int num;
private String msg;
public int getNum() {
return num;
}
public void setNum(int num) {
this.num = num;
}
public String getMsg() {
return msg;
}
public void setMsg(String msg) {
this.msg = msg;
}
public FactoryDemo() {
LOG.info("FactoryDemo no params constructor");
}
public BeanDemo create() {
BeanDemo beanDemo = new BeanDemo();
LOG.info("invoke create without args,beanDemo:" + beanDemo);
return beanDemo;
}
public BeanDemo create(int num, String msg) {
BeanDemo beanDemo = new BeanDemo();
beanDemo.setMsg(msg);
beanDemo.setNum(num);
LOG.info("invoke create with args,beanDemo:" + "[" + beanDemo + "]" + beanDemo.getMsg() + "," + beanDemo.getNum());
return beanDemo;
}
}
public class BeanDemo {
private final static Log LOG = LogFactory.getLog(BeanDemo.class);
private int num;
private String msg;
public BeanDemo() {
LOG.info("BeanDemo constructor");
}
public int getNum() {
return num;
}
public void setNum(int num) {
this.num = num;
}
public String getMsg() {
return msg;
}
public void setMsg(String msg) {
this.msg = msg;
}
}
调用无参的factoryMethod
@Test
public void factoryBeanNameTestWithoutArgs() {
AnnotationConfigApplicationContext context = new AnnotationConfigApplicationContext();
context.register(FactoryDemo.class);
GenericBeanDefinition definition = new GenericBeanDefinition();
// 设置factoryBean
definition.setFactoryBeanName("factoryDemo");
definition.setFactoryMethodName("create");
definition.setBeanClass(BeanDemo.class);
context.registerBeanDefinition("beanDemo", definition);
context.refresh();
System.out.println(context.getBean(BeanDemo.class));
}
调用有参factoryMethod
@Test
public void factoryBeanNameWithArgsTest() {
AnnotationConfigApplicationContext context = new AnnotationConfigApplicationContext();
context.register(FactoryDemo.class);
GenericBeanDefinition definition = new GenericBeanDefinition();
// 设置factoryBean
definition.setFactoryBeanName("factoryDemo");
definition.setFactoryMethodName("create");
ConstructorArgumentValues argumentValues = new ConstructorArgumentValues();
argumentValues.addGenericArgumentValue("test", "java.lang.String");
argumentValues.addGenericArgumentValue(1, "int");
definition.setConstructorArgumentValues(argumentValues);
definition.setBeanClass(BeanDemo.class);
context.registerBeanDefinition("beanDemo", definition);
context.refresh();
System.out.println(context.getBean(BeanDemo.class));
}
beanDefinition有factoryMethod属性和supplier属性
@Test
public void supplierOrderTest() {
AnnotationConfigApplicationContext context = new AnnotationConfigApplicationContext();
context.register(FactoryDemo.class);
GenericBeanDefinition definition = new GenericBeanDefinition();
// 设置factoryBean
definition.setFactoryBeanName("factoryDemo");
definition.setFactoryMethodName("create");
definition.setBeanClass(BeanDemo.class);
context.registerBeanDefinition("beanDemo", definition);
definition.setInstanceSupplier((Supplier<BeanDemo>) BeanDemo::new);
context.refresh();
Assertions.assertNotNull(context.getBean("beanDemo"));
}
此时优先执行supplier逻辑；
Spring创建对象方式的整理图
Spring实例化策略整理
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