Spring源码阅读（四）—容器的功能拓展ApplicationContext

ApplicationContext和BeanFactory都用于Bean的加载，ApplicationContext包含BeanFactory的所有功能，创建的上下文环境是BeanFactory的功能拓展．

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原文地址：Spring源码阅读（四）—容器的功能拓展ApplicationContext

(0) ApplicationContext和BeanFactory的区别

• ApplicationContext（应用上下文）和BeanFactory（bean工厂）是Spring的两种容器，ApplicationContext是BeanFactory的功能拓展．

• BeanFactroy采用的是延迟加载形式来注入依赖的，只有在调用getBean()的时候才对该Bean进行加载实例化.而ApplicationContext是在容器启动时，一次性创建了所有的Bean。这样，在容器启动时，我们就可以发现Spring中存在的配置错误。

• ApplicationContext扩展了ResourceLoader(资源加载器)接口，从而可以用来加载多个Resource，而BeanFactory是没有扩展ResourceLoader ，只能加载单个资源文件．

• BeanFactory是不支持国际化功能的，因为BeanFactory没有扩展Spring中MessageResource接口。相反，由于ApplicationContext扩展了MessageResource接口提供了国际化的消息访问功能．

• ApplicationContext实现了强大的事件机制(Event)

(1) ApplicationContext上下文的入口

• 初始化ApplicationContext

ApplicationContext context = new ClassPathXmlApplicationContext("applicationContext.xml");HelloWorld helloWorld = context.getBean("hello",HelloWorld.class);

• 调用setConfigLocations()方法将配置文件加载进内存，调用refresh()方法进行上下文的初始化

public ClassPathXmlApplicationContext(String[] configLocations, boolean refresh, ApplicationContext parent) throws BeansException {    super(parent);    this.setConfigLocations(configLocations);    if(refresh) {        this.refresh();    }}

(2) ApplicationContext上下文的初始化

上下文初始化主要步骤：

• 调用prepareRefresh()方法刷新上下文环境，对系统属性和环境变量的初始化进行验证；

• 调用obtainFreshBeanFactory()方法读取XML配置文件初始化BeanFactory，实现了BeanFactory的功能．

• 调用prepareBeanFactory()方法对BeanFactory进行功能拓展

• 实现事件机制

• 初始化剩下的所有单例bean，进行bean的初始化和依赖的注入

public void refresh() throws BeansException, IllegalStateException {    Object var1 = this.startupShutdownMonitor;    synchronized(this.startupShutdownMonitor) {        this.prepareRefresh();        ConfigurableListableBeanFactory beanFactory = this.obtainFreshBeanFactory();        this.prepareBeanFactory(beanFactory);        try {            this.postProcessBeanFactory(beanFactory);            this.invokeBeanFactoryPostProcessors(beanFactory);            this.registerBeanPostProcessors(beanFactory);            this.initMessageSource();            this.initApplicationEventMulticaster();            this.onRefresh();            this.registerListeners();            this.finishBeanFactoryInitialization(beanFactory);            this.finishRefresh();        } catch (BeansException var5) {            this.logger.warn("Exception encountered during context initialization - cancelling refresh attempt", var5);            this.destroyBeans();            this.cancelRefresh(var5);            throw var5;        }    }}

1.调用obtainFreshBeanFactory()方法初始化BeanFactory

• 调用customizeBeanFactory()定制BeanFactory提供＠Autowired支持等

• 调用loadBeanDefinitions()方法从XML配置文件中装载bean

protected ConfigurableListableBeanFactory obtainFreshBeanFactory() {    this.refreshBeanFactory();    ConfigurableListableBeanFactory beanFactory = this.getBeanFactory();    if(this.logger.isDebugEnabled()) {        this.logger.debug("Bean factory for " + this.getDisplayName() + ": " + beanFactory);    }    return beanFactory;}

2.BeanFactory的功能拓展

• 调用invokeBeanFactoryPostProcessors()方法激活所有注册的BeanBeanFactoryPostProcessor后处理器（对象是BeanFactory）.BeanBeanFactoryPostProcessor是在注册Bean工厂加载完所有Bean后执行，通过实现BeanFactoryPostProcessor接口进行注册．

this.invokeBeanFactoryPostProcessors(beanFactory);

• 调用registerBeanPostProcessors()方法注册BeanPostProcessor后处理器（对象是Bean）.BeanPostProcessor是在bean实例化后调用，用于功能拓展．BeanPostProcessor注册的方法是实现InstantiationAwareBeanPostProcessor接口．

this.registerBeanPostProcessors(beanFactory);

• 调用initMessageSource()方法初始化Message源，进行国际化处理

this.initMessageSource();

• 实现事件机制

  • 调用initApplicationMuticaster()方法初始化消息广播器，广播器用于存放监听器并在合适的时候调用监听器．

  • 调用registerListeners()方法注册bean中的所有监听器listener

this.initApplicationEventMulticaster();this.registerListeners();

• 调用finishBeanFactoryInitialization()方法加载所有的bean实例，并进行依赖注入（区别于BeanFactory的重要一点）

调用preInstantiateSingletons()方法进行bean的实例化和依赖注入

protected void finishBeanFactoryInitialization(ConfigurableListableBeanFactory beanFactory) {    if(beanFactory.containsBean("conversionService") && beanFactory.isTypeMatch("conversionService", ConversionService.class)) {        beanFactory.setConversionService((ConversionService)beanFactory.getBean("conversionService", ConversionService.class));    }    String[] weaverAwareNames = beanFactory.getBeanNamesForType(LoadTimeWeaverAware.class, false, false);    String[] var3 = weaverAwareNames;    int var4 = weaverAwareNames.length;    for(int var5 = 0; var5 < var4; ++var5) {        String weaverAwareName = var3[var5];        this.getBean(weaverAwareName);    }    beanFactory.setTempClassLoader((ClassLoader)null);    beanFactory.freezeConfiguration();    beanFactory.preInstantiateSingletons();}

(3) 总结

ApplicationContext上下文的初始化主要是进行了初始化BeanFactory，并在此基础上进行功能拓展比如事件机制，后处理器等，最后对BeanFactory中的所有bean进行实例化和依赖注入．