spring源码分析——xml加载流程
这里我们以最基础的xml配置的形式来解析，看一下spring启动流程的初始步骤：
一：使用spring
引入依赖：
<dependency>
<groupId>org.springframework</groupId>
<artifactId>spring-context</artifactId>
<version>${spring-context.version}</version>
</dependency>
<dependency>
<groupId>ch.qos.logback</groupId>
<artifactId>logback-classic</artifactId>
<version>${logback-classic.version}</version>
</dependency>
配置spring-context.xml文件，下面的properties和order-context的引入可以注释掉：
<?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" xmlns:myname="http://www.lexueba.com/schema/user" xmlns:p="http://www.springframework.org/schema/p" xmlns:c="http://www.springframework.org/schema/c" xmlns:aop="http://www.springframework.org/schema/aop" 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.xsd http://www.lexueba.com/schema/user http://www.lexueba.com/schema/user.xsd http://www.springframework.org/schema/aop https://www.springframework.org/schema/aop/spring-aop.xsd"> <!--配置扫描路径--> <context:component-scan base-package="com.hello"/> <myname:user id="customId" name="hello"/> <aop:aspectj-autoproxy/> <!-- 传统set注入用法 <bean id="person" name="person1,person2,person3" class="com.hello.model.Person"> <property name="id" value="123"></property> <property name="name" value="tom"></property> </bean> --> <!-- 自定义标签set属性注入--> <bean id="person" name="person1,person2,person3" class="com.hello.model.Person" p:id="1234" p:name="tomcat"/> <!--构造器注入--> <bean id="student1" class="com.hello.model.Student" c:_0="300" c:_1="400" primary="true"> <!-- <constructor-arg index="0" value="100"/> <constructor-arg index="1" value="200"/> --> </bean> <!--meta元数据设置--> <bean id="orderService" class="com.hello.model.OrderService"> <meta key="test" value="testValue"></meta> </bean> <!--lookup-method标签可以动态的赋值bean,bean的值从teacher替换为student--> <bean id="userStudyService" class="com.hello.model.UserStudyService"> <lookup-method name="getUser" bean="student1"></lookup-method> </bean> <bean id="teacher" class="com.hello.model.Teacher"/> <!--replaced-method标签可以摒弃原来的业务--> <bean id="cat" class="com.hello.model.Cat"> <replaced-method name="sing" replacer="tomcat"/> </bean> <bean id="tomcat" class="com.hello.model.TomCat"/> <!--qualifier的作用等于给bean再起一个名字，注入的时候可以使用这个名字--> <bean id="testQualifier1" class="com.hello.model.TestQualifier"> <property name="id" value="111"/> <qualifier type="org.springframework.beans.factory.annotation.Qualifier" value="qf"/> </bean> <bean id="testQualifier2" class="com.hello.model.TestQualifier"> <property name="id" value="222"/> </bean> <!--factory-bean的用法--> <bean id="myFactoryBean" class="com.hello.model.MyFactoryBean"/> <bean id="user" factory-bean="myFactoryBean" factory-method="user"/> <!--导入其他模块的配置文件--> <import resource="order-context.xml"/> <!--加载properties配置文件--> <context:property-placeholder location="classpath*:*.properties" /> </beans>
测试代码：
public class TestSpringContext {
public static void main(String[] args) {
ClassPathXmlApplicationContext context = new ClassPathXmlApplicationContext("spring-context.xml");
System.out.println("person: "+context.getBean("person3"));
System.out.println("student: "+context.getBean("student1"));
System.out.println("orderService: "+context.getBean("orderService"));
UserStudyService userStudyService = (UserStudyService)context.getBean("userStudyService");
userStudyService.doStudy();
Cat cat = context.getBean(Cat.class);
cat.sing();
Teacher teacher = context.getBean(Teacher.class);
teacher.study();
User user = (User)context.getBean("hello");
System.out.println(user);
Child child = (Child)context.getBean("child");
System.out.println("child: "+child);
context.getBean(TestAutowiredModel.class).print();
context.getBean("myFactoryBeanDemo");
TestAopService testAopService = context.getBean(TestAopService.class);
testAopService.test();
}
}
看日志可以spring容器已经正常启动，对象以及对象之间的依赖关系已经交给spring容器维护
二：基于xml配置的加载流程分析
这条语句执行完，spring容器就已经启动完成了，下面我们来看一下，入参就是xml配置文件：
ClassPathXmlApplicationContext context = new ClassPathXmlApplicationContext("spring-context.xml");
有一个setConfigLocations方法，入参就是上面的xml文件路径，
public ClassPathXmlApplicationContext(
String[] configLocations, boolean refresh, @Nullable ApplicationContext parent)
throws BeansException {
super(parent);
// 初始化配置文件xml的位置（AbstractRefreshableConfigApplicationContext）
setConfigLocations(configLocations);
if (refresh) {
// spring容器启动的主流程
refresh();
}
}
public void setConfigLocations(@Nullable String... locations) {
if (locations != null) {
Assert.noNullElements(locations, "Config locations must not be null");
this.configLocations = new String[locations.length];
for (int i = 0; i < locations.length; i++) {
this.configLocations[i] = resolvePath(locations[i]).trim();
}
}
else {
this.configLocations = null;
}
}
维护到了AbstractRefreshableConfigApplicationContext的属性上：
回过头来看刚才的创建ApplicationContext对象的构造方法，spring容器的主要逻辑都是在这里：
进如refresh，实际上这个是父类AbstractApplicationContext中的方法：
public void refresh() throws BeansException, IllegalStateException {
synchronized (this.startupShutdownMonitor) {
// Prepare this context for refreshing.
// 准备刷新spring上下文，可以不看
prepareRefresh();
// Tell the subclass to refresh the internal bean factory.
// 1：创建beanFactory工厂 2：解析xml文件，扫描注解 生成beanDefinition对象 3：注册到beanDefinitionRegistry缓存中
ConfigurableListableBeanFactory beanFactory = obtainFreshBeanFactory();
// Prepare the bean factory for use in this context.
// beanFactory 的一些准备工作，可以不看
prepareBeanFactory(beanFactory);
try {
// Allows post-processing of the bean factory in context subclasses.
// 钩子方法，由子类实现
postProcessBeanFactory(beanFactory);
// Invoke factory processors registered as beans in the context.
// 注册beanFactoryPostProcessor对象
invokeBeanFactoryPostProcessors(beanFactory);
// Register bean processors that intercept bean creation.
// 注册beanPostProcessor实例，在bean创建的时候实现拦截
registerBeanPostProcessors(beanFactory);
// Initialize message source for this context.
initMessageSource();
// Initialize event multicaster for this context.
initApplicationEventMulticaster();
// Initialize other special beans in specific context subclasses.
onRefresh();
// Check for listener beans and register them.
registerListeners();
// Instantiate all remaining (non-lazy-init) singletons.
/**
* 在之前已经实例化了BeanFactoryPostProcessor以及beanPostProcessor
* 下面开始实例化剩下的所有非懒加载的单例对象
*/
finishBeanFactoryInitialization(beanFactory);
// Last step: publish corresponding event.
finishRefresh();
}
catch (BeansException ex) {
if (logger.isWarnEnabled()) {
logger.warn("Exception encountered during context initialization - " +
"cancelling refresh attempt: " + ex);
}
// Destroy already created singletons to avoid dangling resources.
destroyBeans();
// Reset 'active' flag.
cancelRefresh(ex);
// Propagate exception to caller.
throw ex;
}
finally {
// Reset common introspection caches in Spring's core, since we
// might not ever need metadata for singleton beans anymore...
resetCommonCaches();
}
}
}
我们这里挑选重要的步骤进行分析，不重要的方法直接跳过了
这一节主要看一下这个方法，从英文看，是让子类刷新内部的bean工厂
// Tell the subclass to refresh the internal bean factory. // 1：创建beanFactory工厂 2：解析xml文件，扫描注解 生成beanDefinition对象 3：注册到beanDefinitionRegistry缓存中 ConfigurableListableBeanFactory beanFactory = obtainFreshBeanFactory();
protected ConfigurableListableBeanFactory obtainFreshBeanFactory() {
refreshBeanFactory();
return getBeanFactory();
}
我们看一下refreshBeanFactory，这个方法是钩子方法，在AbstractApplicationContext中并没有实现，而是交给子类实现：
调到了AbstractRefreshableApplicationContext，这个判断如果beanFactory存在，就销毁实例，关闭工厂，然后重新创建一个beanFactory
protected final void refreshBeanFactory() throws BeansException {
//如果beanFactory存在，就销毁实例，关闭工厂
if (hasBeanFactory()) {
destroyBeans();
closeBeanFactory();
}
try {
// 创建一个beanFactory工厂容器
DefaultListableBeanFactory beanFactory = createBeanFactory();
beanFactory.setSerializationId(getId());
customizeBeanFactory(beanFactory);
// 加载xml配置文件
loadBeanDefinitions(beanFactory);
synchronized (this.beanFactoryMonitor) {
this.beanFactory = beanFactory;
}
}
catch (IOException ex) {
throw new ApplicationContextException("I/O error parsing bean definition source for " + getDisplayName(), ex);
}
}
加载xml配置，把beanFactory作为入参传入
// 加载xml配置文件 loadBeanDefinitions(beanFactory);
调用到AbstractXmlApplicationContext，这个类继承了AbstractRefreshableConfigApplicationContext类，这个类就是刚才setConfigLocation方法所在的类：
protected void loadBeanDefinitions(DefaultListableBeanFactory beanFactory) throws BeansException, IOException {
// Create a new XmlBeanDefinitionReader for the given BeanFactory.
// 为beanFactory创建一个xmlBean的解析器
XmlBeanDefinitionReader beanDefinitionReader = new XmlBeanDefinitionReader(beanFactory);
// Configure the bean definition reader with this context's
// resource loading environment.
beanDefinitionReader.setEnvironment(this.getEnvironment());
beanDefinitionReader.setResourceLoader(this);
beanDefinitionReader.setEntityResolver(new ResourceEntityResolver(this));
// Allow a subclass to provide custom initialization of the reader,
// then proceed with actually loading the bean definitions.
initBeanDefinitionReader(beanDefinitionReader);
// 加载xml配置
loadBeanDefinitions(beanDefinitionReader);
}
然后将xml解析的任务委托给了XmlBeanDefinitionReader对象来操作，调用loadBeanDefinitions
protected void loadBeanDefinitions(XmlBeanDefinitionReader reader) throws BeansException, IOException {
Resource[] configResources = getConfigResources();
if (configResources != null) {
reader.loadBeanDefinitions(configResources);
}
// 在第一步classPathXmlApplicationContext构造器中，已经初始化了configLocation
String[] configLocations = getConfigLocations();
if (configLocations != null) {
// xml的阅读器加载xml配置文件
reader.loadBeanDefinitions(configLocations);
}
}
委托给reader来解析 reader.loadBeanDefinitions()
public int loadBeanDefinitions(String... locations) throws BeanDefinitionStoreException {
Assert.notNull(locations, "Location array must not be null");
int count = 0;
// 如果有多个xml文件，会循环解析，我们这里只有一个xml配置文件
for (String location : locations) {
count += loadBeanDefinitions(location);
}
return count;
}
Xml解析器将xml所在的路径location，封装成一个资源文件Resource，然后调用loadBeanDefinitions（resources）
public int loadBeanDefinitions(String location, @Nullable Set<Resource> actualResources) throws BeanDefinitionStoreException {
ResourceLoader resourceLoader = getResourceLoader();
if (resourceLoader == null) {
throw new BeanDefinitionStoreException(
"Cannot load bean definitions from location [" + location + "]: no ResourceLoader available");
}
if (resourceLoader instanceof ResourcePatternResolver) {
// Resource pattern matching available.
try {
// 首先把location路径封装成一个资源文件
Resource[] resources = ((ResourcePatternResolver) resourceLoader).getResources(location);
int count = loadBeanDefinitions(resources);
if (actualResources != null) {
Collections.addAll(actualResources, resources);
}
if (logger.isTraceEnabled()) {
logger.trace("Loaded " + count + " bean definitions from location pattern [" + location + "]");
}
return count;
}
catch (IOException ex) {
throw new BeanDefinitionStoreException(
"Could not resolve bean definition resource pattern [" + location + "]", ex);
}
}
else {
// Can only load single resources by absolute URL.
// 这个Resource仅仅能够加载单个的绝对路径的xml配置文件
Resource resource = resourceLoader.getResource(location);
int count = loadBeanDefinitions(resource);
if (actualResources != null) {
actualResources.add(resource);
}
if (logger.isTraceEnabled()) {
logger.trace("Loaded " + count + " bean definitions from location [" + location + "]");
}
return count;
}
}
接着向下看，上一步将resouce包装成可编码的EncodedResource对象，下面的方法，从资源Resource中拿到输入流InputStream，维护到InputSource中，然后调用doLoaderBeanDefinitions解析
public int loadBeanDefinitions(EncodedResource encodedResource) throws BeanDefinitionStoreException {
Assert.notNull(encodedResource, "EncodedResource must not be null");
if (logger.isTraceEnabled()) {
logger.trace("Loading XML bean definitions from " + encodedResource);
}
Set<EncodedResource> currentResources = this.resourcesCurrentlyBeingLoaded.get();
if (currentResources == null) {
currentResources = new HashSet<>(4);
this.resourcesCurrentlyBeingLoaded.set(currentResources);
}
if (!currentResources.add(encodedResource)) {
throw new BeanDefinitionStoreException(
"Detected cyclic loading of " + encodedResource + " - check your import definitions!");
}
try {
// 从resource资源中获取输入流
InputStream inputStream = encodedResource.getResource().getInputStream();
try {
InputSource inputSource = new InputSource(inputStream);
if (encodedResource.getEncoding() != null) {
inputSource.setEncoding(encodedResource.getEncoding());
}
// 加载beanDefinition
return doLoadBeanDefinitions(inputSource, encodedResource.getResource());
}
finally {
inputStream.close();
}
}
catch (IOException ex) {
throw new BeanDefinitionStoreException(
"IOException parsing XML document from " + encodedResource.getResource(), ex);
}
finally {
currentResources.remove(encodedResource);
if (currentResources.isEmpty()) {
this.resourcesCurrentlyBeingLoaded.remove();
}
}
}
将inputSource对象解析成Documet对象，具体的解析细节先不看
protected int doLoadBeanDefinitions(InputSource inputSource, Resource resource)
throws BeanDefinitionStoreException {
try {
// 将输入流解析为Document文件
Document doc = doLoadDocument(inputSource, resource);
int count = registerBeanDefinitions(doc, resource);
if (logger.isDebugEnabled()) {
logger.debug("Loaded " + count + " bean definitions from " + resource);
}
return count;
}
}
解析为document对象，之后就要注册beanDefinition了，在spring的加载过程中，BeanDefinition是一个重要的数据结构，它是在创建对象之前，对象数据的一种存在形式
xml —— beanDefinition ——bean 从xml配置bean ，到解析xml创建 beanDefinition ， 到从beanDefinition实例为 bean对象，这是一个流程。
docoment对象的解析过程委托给了BeanDefinitionDocumentReader对象来完成：
public int registerBeanDefinitions(Document doc, Resource resource) throws BeanDefinitionStoreException {
BeanDefinitionDocumentReader documentReader = createBeanDefinitionDocumentReader();
int countBefore = getRegistry().getBeanDefinitionCount();
// 解析document文件，然后注册registerBeanDefinitions
documentReader.registerBeanDefinitions(doc, createReaderContext(resource));
return getRegistry().getBeanDefinitionCount() - countBefore;
}
public void registerBeanDefinitions(Document doc, XmlReaderContext readerContext) {
this.readerContext = readerContext;
// 注册beanDefinition，将document中root元素传入
doRegisterBeanDefinitions(doc.getDocumentElement());
}
委托给document的解析器，入参为document的根元素，就是spring-context.xml的beans元素：
protected void doRegisterBeanDefinitions(Element root) {
// Any nested <beans> elements will cause recursion in this method. In
// order to propagate and preserve <beans> default-* attributes correctly,
// keep track of the current (parent) delegate, which may be null. Create
// the new (child) delegate with a reference to the parent for fallback purposes,
// then ultimately reset this.delegate back to its original (parent) reference.
// this behavior emulates a stack of delegates without actually necessitating one.
BeanDefinitionParserDelegate parent = this.delegate;
this.delegate = createDelegate(getReaderContext(), root, parent);
if (this.delegate.isDefaultNamespace(root)) {
String profileSpec = root.getAttribute(PROFILE_ATTRIBUTE);
if (StringUtils.hasText(profileSpec)) {
String[] specifiedProfiles = StringUtils.tokenizeToStringArray(
profileSpec, BeanDefinitionParserDelegate.MULTI_VALUE_ATTRIBUTE_DELIMITERS);
// We cannot use Profiles.of(...) since profile expressions are not supported
// in XML config. See SPR-12458 for details.
if (!getReaderContext().getEnvironment().acceptsProfiles(specifiedProfiles)) {
if (logger.isDebugEnabled()) {
logger.debug("Skipped XML bean definition file due to specified profiles [" + profileSpec +
"] not matching: " + getReaderContext().getResource());
}
return;
}
}
}
// 这里有两个钩子方法，典型的模板设计，由子类去实现
preProcessXml(root);
// 具体的解析document对象，注册beanDefinition的逻辑在这里实现
parseBeanDefinitions(root, this.delegate);
postProcessXml(root);
this.delegate = parent;
}
具体的解析工作在parseBeanDefinition中，在这里就是具体解析默认标签和自定义标签的流程。
protected void parseBeanDefinitions(Element root, BeanDefinitionParserDelegate delegate) {
//判断根元素的命名空间是否为空或者是 xmlns="http://www.springframework.org/schema/beans"
if (delegate.isDefaultNamespace(root)) {
NodeList nl = root.getChildNodes();
for (int i = 0; i < nl.getLength(); i++) {
Node node = nl.item(i);
if (node instanceof Element) {
Element ele = (Element) node;
if (delegate.isDefaultNamespace(ele)) {
// 解析默认标签，例如：bean
parseDefaultElement(ele, delegate);
}
else {
// 解析自定义标签 例如：context
delegate.parseCustomElement(ele);
}
}
}
}
else {
delegate.parseCustomElement(root);
}
}
总结：这一节主要是启动spring流程的第一步，解析配置文件，当然我们这里是以xml配置的方式分析，也可能是注解配置的方法，后续再来分析注解方式。
1：创建applicationContext对象，将xml文件的路径维护到AbstractRefreshableApplicationContext的属性上
2：refresh启动spring流程，这里是spring启动的核心流程
3：第一步 obtainBeanFactory ，这这个方法里，会创建bean工厂，加载xml文件，委托给XmlBeanDefinitionReader解析
4：XmlBeanDefinitionReader 将xml字符串路径封装为Resource对象，再转为InputStream流，最后把输入流生成Document对象，然后委托给BeanDefinitionDocumentReader解析。
下面一节来分析一下解析默认标签
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