使用BeanFactory方式加载XML
BeanFactory bf = new XmlBeanFactory(new ClassPathResource("beanTest.xml"));
使用ApplicationContext方式加载XML
ApplicationContext context = new ClassPathXmlApplicationContext("beanTest.xml");
ApplicationContext和BeanFactory两者都是用于加载bean的,但是相比之下,ApplicationContext提供了更多的功能扩展。
以ClassPathXmlApplicationContext作为切入点,开始对整体功能进行分析。
public ClassPathXmlApplicationContext(String configLocation) throws BeansException { this(new String[] {configLocation}, true, null); }
public ClassPathXmlApplicationContext(String[] configLocations, boolean refresh, ApplicationContext parent) throws BeansException { super(parent); setConfigLocations(configLocations); if (refresh) { refresh(); } }
ClassPathXmlApplicationContext中可以将配置文件路径以数组的方式传入,ClassPathXmlApplicationContext可以对数组进行解析并进行加载。而对于解析及功能实现都在refresh()中实现。
public void setConfigLocations(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; } }
此函数主要用于解析给定的路径数组,如果数组中包含特殊符号,如${var},那么resolvePath中会搜寻匹配系统变量并替换。
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) { // Destroy already created singletons to avoid dangling resources. destroyBeans(); // Reset 'active' flag. cancelRefresh(ex); // Propagate exception to caller. throw ex; } } }
refresh函数中包含了几乎ApplicationContext中提供的全部功能,而且逻辑非常清晰明了。
(1)初始化前的准备工作,例如对系统属性或者环境变量进行准备验证。
(2)初始化BeanFactory,并进行XML文件读取。
(3)对BeanFactory进行各种功能填充。
(4)子类覆盖方法做额外处理。
(5)激活各种BeanFactory处理器。
(6)注册拦截bean创建的bean处理器,这里只是注册,真正的调用是在getBean时候。
(7)为上下文初始化Message源,即对不同语言的消息体进行国际化处理。
(8)初始化应用消息广播器,并放入applicationEventMulticaster中。
(9)留给子类来初始化其他的bean。
(10)在所有注册的bean中查找listener bean,注册到消息广播中。
(11)初始化剩下的单实例(非惰性)。
(12)完成刷新过程,通知生命周期处理器lifecycleProcessor刷新过程,同时发出ContextRefreshEvent通知别人。