spring容器启动的加载过程(一)
使用spring，我们在web.xml都会配置ContextLoaderListener
<listener> <listener-class> org.springframework.web.context.ContextLoaderListener </listener-class> </listener>
public class ContextLoaderListener extends ContextLoader implements ServletContextListener {
//由于他继承自ContextLoader，加载的时候当然会先加载他啦，那我们来看看这个类
}
ContextLoader这个类有一段静态代码块
private static final String DEFAULT_STRATEGIES_PATH = "ContextLoader.properties";//这个文件是在org.springframework.web.context.ContextLoader.properties他里面是
org.springframework.web.context.WebApplicationContext=org.springframework.web.context.support.XmlWebApplicationContext //这个后面再研究 以后就会把spring所有重要的东西都能看到了。 private static final Properties defaultStrategies; static { // Load default strategy implementations from properties file. // This is currently strictly internal and not meant to be customized // by application developers. try { ClassPathResource resource = new ClassPathResource(DEFAULT_STRATEGIES_PATH, ContextLoader.class); defaultStrategies = PropertiesLoaderUtils.loadProperties(resource);//根据上面的properties文件，就能得到一个默认的properties了。 } catch (IOException ex) { throw new IllegalStateException("Could not load 'ContextLoader.properties': " + ex.getMessage()); } }
第一步：我们在看看ContextLoaderListener的这个方法，在容器启动的时候，他会扫描web.xml的listener配置，然后自动调用Listener的contextInitialized初始化方法。
public void contextInitialized(ServletContextEvent event) { this.contextLoader = createContextLoader(); if (this.contextLoader == null) { this.contextLoader = this; } this.contextLoader.initWebApplicationContext(event.getServletContext()); }
第二步：initWebApplicationContext初始化web应用上下文
public WebApplicationContext initWebApplicationContext(ServletContext servletContext) { if (servletContext.getAttribute(WebApplicationContext.ROOT_WEB_APPLICATION_CONTEXT_ATTRIBUTE) != null) { throw new IllegalStateException( "Cannot initialize context because there is already a root application context present - " + "check whether you have multiple ContextLoader* definitions in your web.xml!"); } Log logger = LogFactory.getLog(ContextLoader.class); servletContext.log("Initializing Spring root WebApplicationContext"); if (logger.isInfoEnabled()) { logger.info("Root WebApplicationContext: initialization started"); } long startTime = System.currentTimeMillis(); try { // Store context in local instance variable, to guarantee that // it is available on ServletContext shutdown. if (this.context == null) { this.context = createWebApplicationContext(servletContext);//判断是否有WebApplicationContext，没有则创建，创建得到的是ConfigurableWebApplicationContext } if (this.context instanceof ConfigurableWebApplicationContext) { ConfigurableWebApplicationContext cwac = (ConfigurableWebApplicationContext) this.context; if (!cwac.isActive()) { //上下文尚未活动 // The context has not yet been refreshed -> provide services such as // setting the parent context, setting the application context id, etc if (cwac.getParent() == null) { // The context instance was injected without an explicit parent -> // determine parent for root web application context, if any. ApplicationContext parent = loadParentContext(servletContext);//决定根Web应用程序环境是否存在父应用程序环境，一般是返回null cwac.setParent(parent); } configureAndRefreshWebApplicationContext(cwac, servletContext);//在这里是初始化web应用上下文的入口 ,spring的依赖注入也从这里开始了。 } } servletContext.setAttribute(WebApplicationContext.ROOT_WEB_APPLICATION_CONTEXT_ATTRIBUTE, this.context);//把创建的根Web应用程序环境保存到Servlet环境中，每个派遣器Servlet加载的子环境会应用这个环境作为父环境 ClassLoader ccl = Thread.currentThread().getContextClassLoader();//取得线程的类加载器 if (ccl == ContextLoader.class.getClassLoader()) { currentContext = this.context;//如果线程和本类拥有相同的类加载器，则使用静态变量保存即可，因为同一类加载器加载同一份静态变量 } else if (ccl != null) { currentContextPerThread.put(ccl, this.context);//如果线程和本类拥有不同的类加载器，则使用线程的类加载器作为键值保存在一个映射对象里，保证析构时能拿到Web应用程序环境进行关闭操作 } if (logger.isDebugEnabled()) { logger.debug("Published root WebApplicationContext as ServletContext attribute with name [" + WebApplicationContext.ROOT_WEB_APPLICATION_CONTEXT_ATTRIBUTE + "]"); } if (logger.isInfoEnabled()) { long elapsedTime = System.currentTimeMillis() - startTime; logger.info("Root WebApplicationContext: initialization completed in " + elapsedTime + " ms"); } return this.context; } catch (RuntimeException ex) { logger.error("Context initialization failed", ex); servletContext.setAttribute(WebApplicationContext.ROOT_WEB_APPLICATION_CONTEXT_ATTRIBUTE, ex);//如果产生任何异常，则保存异常对象到Servlet环境里 throw ex; } catch (Error err) { logger.error("Context initialization failed", err); servletContext.setAttribute(WebApplicationContext.ROOT_WEB_APPLICATION_CONTEXT_ATTRIBUTE, err);//如果产生任何错误，则保存错误对象到Servlet环境里 throw err; } }
第三步：得到具体的应用上下文
public static final String CONTEXT_CLASS_PARAM = "contextClass"; private static final String DEFAULT_STRATEGIES_PATH = "ContextLoader.properties"; private static final Properties defaultStrategies; //这个静态代码块，会去加载相同目录下的ContextLoader.properties，这个目录是org.springframework.web.context，这个配置文件的配置信息就只有org.springframework.web.context.WebApplicationContext=org.springframework.web.context.support.XmlWebApplicationContext static { // Load default strategy implementations from properties file. // This is currently strictly internal and not meant to be customized // by application developers. try { ClassPathResource resource = new ClassPathResource(DEFAULT_STRATEGIES_PATH, ContextLoader.class); defaultStrategies = PropertiesLoaderUtils.loadProperties(resource); } catch (IOException ex) { throw new IllegalStateException("Could not load 'ContextLoader.properties': " + ex.getMessage()); } } protected WebApplicationContext createWebApplicationContext(ServletContext sc) { Class<?> contextClass = determineContextClass(sc);//决定要得到哪个ContextClass if (!ConfigurableWebApplicationContext.class.isAssignableFrom(contextClass)) { throw new ApplicationContextException("Custom context class [" + contextClass.getName() + "] is not of type [" + ConfigurableWebApplicationContext.class.getName() + "]"); } return (ConfigurableWebApplicationContext) BeanUtils.instantiateClass(contextClass); //实例化Web应用程序环境类 } protected Class<?> determineContextClass(ServletContext servletContext) { String contextClassName = servletContext.getInitParameter(CONTEXT_CLASS_PARAM);//获取web.xml配置的contextClass if (contextClassName != null) {//配置了contextClass,返回具体的Class try { return ClassUtils.forName(contextClassName, ClassUtils.getDefaultClassLoader()); } catch (ClassNotFoundException ex) { throw new ApplicationContextException( "Failed to load custom context class [" + contextClassName + "]", ex); } } else { contextClassName = defaultStrategies.getProperty(WebApplicationContext.class.getName());//在上面的静态代码块中已经加载了XmlWebApplicationContext，返回的是XmlWebApplicationContext的全路径名：org.springframework.web.context.support.XmlWebApplicationContext try { return ClassUtils.forName(contextClassName, ContextLoader.class.getClassLoader());//没有配置contextClass,则通过配置文件，返回了XmlWebApplicationContext的class } catch (ClassNotFoundException ex) { throw new ApplicationContextException( "Failed to load default context class [" + contextClassName + "]", ex); } } }
第四步：用于封装ApplicationContext数据并且初始化所有相关Bean对象。它会从web.xml中读取名为contextConfigLocation的配置，这就是spring xml数据源设置，然后放到ApplicationContext中，最后调用传说中的refresh方法执行所有Java对象的创建。
public static final String CONFIG_LOCATION_PARAM = "contextConfigLocation"; 在wen.xml中配置的位置 protected void configureAndRefreshWebApplicationContext(ConfigurableWebApplicationContext wac, ServletContext sc) { if (ObjectUtils.identityToString(wac).equals(wac.getId())) { // The application context id is still set to its original default value // -> assign a more useful id based on available information String idParam = sc.getInitParameter(CONTEXT_ID_PARAM); //设置Web应用程序环境的ID if (idParam != null) { wac.setId(idParam); } else { // Generate default id... //如果 Servlet规范 <= 2.4，则使用web.xml里定义的应用程序名字定义Web应用程序名 if (sc.getMajorVersion() == 2 && sc.getMinorVersion() < 5) { // Servlet <= 2.4: resort to name specified in web.xml, if any. wac.setId(ConfigurableWebApplicationContext.APPLICATION_CONTEXT_ID_PREFIX + ObjectUtils.getDisplayString(sc.getServletContextName())); } else { // 如果Servlet规范是 2.5， 则使用配置的ContextPath定义Web应用程序名 wac.setId(ConfigurableWebApplicationContext.APPLICATION_CONTEXT_ID_PREFIX + ObjectUtils.getDisplayString(sc.getContextPath())); } } } //保存Servlet环境 wac.setServletContext(sc); String initParameter = sc.getInitParameter(CONFIG_LOCATION_PARAM);//这里得到"contextConfigLocation"配置的值:classpath*:spring-config.xml, if (initParameter != null) { wac.setConfigLocation(initParameter);//设置保存ConfigLocation，待后面加载的时候，扫描里面的配置 } customizeContext(sc, wac);//提供子类可互换Web应用程序环境的机会 占位符方法 wac.refresh();//刷新Web应用程序环境以加载Bean定义,这里才是把我们XML里定义的bean放入容器的时候 }
"contextConfigLocation"在web.xml的配置
<context-param> <param-name>contextConfigLocation</param-name> <param-value> classpath*:spring-config.xml, </param-value> </context-param>
第五步：bean的注入
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();//告诉子类刷新内部bean工厂。 // Prepare the bean factory for use in this context. prepareBeanFactory(beanFactory);//准备bean工厂给上下文使用 try { // Allows post-processing of the bean factory in context subclasses. postProcessBeanFactory(beanFactory);//允许在上下文后处理bean工厂的子类 // Invoke factory processors registered as beans in the context. invokeBeanFactoryPostProcessors(beanFactory);//调用处理器工厂注册的bean上下文 // Register bean processors that intercept bean creation. registerBeanPostProcessors(beanFactory);注册bean拦截器拦截bean的创建 // Initialize message source for this context. initMessageSource();//给上下文初始化消息来源 // Initialize event multicaster for this context. initApplicationEventMulticaster();//给上下文初始化事件多播 // Initialize other special beans in specific context subclasses.//在特定上下文初始化其他特殊bean子类 onRefresh(); // Check for listener beans and register them. registerListeners();//检查监听器bean并注册他们 // Instantiate all remaining (non-lazy-init) singletons. finishBeanFactoryInitialization(beanFactory);//实例化所有剩余(non-lazy-init)单例对象 // Last step: publish corresponding event. finishRefresh();//发布相应的事件 } catch (BeansException ex) { // Destroy already created singletons to avoid dangling resources. destroyBeans();//销毁已经创建的单例，避免悬挂的资源 // Reset 'active' flag. cancelRefresh(ex);//重置“活跃”标志 // Propagate exception to caller. throw ex; } } }
