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．