Spring——Spring IOC容器初始化过程详解编程语言

第一个过程是Resource资源定位。这个Resouce指的是BeanDefinition的资源定位。这个过程就是容器找数据的过程，就像水桶装水需要先找到水一样。（将xml, db.properties等文件打包成一个BeanDefinition） 第二个过程是BeanDefinition的载入过程。这个载入过程是把用户定义好的Bean表示成Ioc容器内部的数据结构，而这个容器内部的数据结构就是BeanDefition。（将BeanDefinition载入，这是Bean就产生了，只不过还没实例化） ​ 第三个过程是向IOC容器注册这些BeanDefinition的过程，这个过程就是将前面的BeanDefition保存到HashMap中的过程。（实例化出这些Bean，由反射完成）

所以实际上IOC注入的那个容器，实际上就是HashMap

Spring 初始化流程

我们从这一步打断点进入，一步步剖析Spring启动的过程

ApplicationContext context = new ClassPathXmlApplicationContext("application.xml"); 

接下来会进入AbstractApplicationContext类的静态初始块，AbstractApplicationContext是ClassPathXmlApplicationContext的父类，下面附上它们的继承关系

static {

 // Eagerly load the ContextClosedEvent class to avoid weird classloader issues 

 // on application shutdown in WebLogic 8.1. (Reported by Dustin Woods.) 

 ContextClosedEvent.class.getName(); 

这句话没有什么特别的实际作用，我们接下去

 /** 

 * Create a new ClassPathXmlApplicationContext, loading the definitions 

 * from the given XML file and automatically refreshing the context. 

 * @param configLocation resource location 

 * @throws BeansException if context creation failed 

 public ClassPathXmlApplicationContext(String configLocation) throws BeansException {

 this(new String[] {

 configLocation}, true, null); 

其中的this构造方法，是下面这一个

 /** 

 * Create a new ClassPathXmlApplicationContext with the given parent, 

 * loading the definitions from the given XML files. 

 * @param configLocations array of resource locations 

 * @param refresh whether to automatically refresh the context, 

 * loading all bean definitions and creating all singletons. 

 * Alternatively, call refresh manually after further configuring the context. 

 * @param parent the parent context 

 * @throws BeansException if context creation failed 

 * @see #refresh() 

 public ClassPathXmlApplicationContext( 

 String[] configLocations, boolean refresh, @Nullable ApplicationContext parent) 

 throws BeansException {

里面的super(parent)会调用一系列父类的的构造方法，最终到达AbstractApplicationContext的构造方法，这实际上是一堆父类容器的初始过程。接下来的setConfigLocations则是解析xml文件**（资源定位过程）**，将所有的配置项读取到Spring中保存（这时候一个BeanDefinition就创建好了）

最重要的Spring初始化过程其实都在refresh方法里

public void refresh() throws BeansException, IllegalStateException {

 synchronized (this.startupShutdownMonitor) {

 // Prepare this context for refreshing. 

 prepareRefresh(); 

 // Tell the subclass to refresh the internal bean factory. 

 ConfigurableListableBeanFactory beanFactory = obtainFreshBeanFactory(); 

 // Prepare the bean factory for use in this context. 

 prepareBeanFactory(beanFactory); 

 try {

 // Allows post-processing of the bean factory in context subclasses. 

 postProcessBeanFactory(beanFactory); 

 // Invoke factory processors registered as beans in the context. 

 invokeBeanFactoryPostProcessors(beanFactory); 

 // Register bean processors that intercept bean creation. 

 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. 

 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 Springs core, since we 

 // might not ever need metadata for singleton beans anymore... 

 resetCommonCaches(); 

未完待续…

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