自我分析-Spring IOC在Web应用的启动和销毁

  Spring IOC容器通过ServletContextListener对servlet容器的生命周期监听，从而实现了IOC的启动和销毁。

    注意：

1.分析框架代码时，要常使用类继承、调用关系等快捷键，可以更高效的学习，快捷键可以设置成你习惯的按键；

2.本文重在怎么自我分析框架代码，所以对其中解析需自己实际跟踪代码实践方可；

3.spring源代码版本 spring-framework-3.2.1.RELEASE。

预览

javax.servlet.ServletContext，Servlet容器接口。

javax.servlet.ServletContextListener，Servlet容器生命周期监听接口。

org.springframework.web.context.ContextLoaderListener，Spring IOC容器生命周期监听类。

org.springframework.web.context.ContextLoader，Spring IOC容器启动和销毁。

配置-监听ServletContext生命周期

在web.xml中spring配置了对ServletContext生命周期的监听，当Web容器启动和销毁时，触发Spring定义的IOC容器的启动和销毁，具体配置如下：

<listener><listener-class>org.springframework.web.context.ContextLoaderListener</listener-class></listener>

入口-ContextLoaderListener对Spring IOC初始化和销毁

当web容器启动时会触发contextInitialized方法对spring ioc容器进行初始化，销毁时会触发contextDestroyed方法对spring ioc容器进行销毁，ServletContextListener接口如下：

    public void contextInitialized ( ServletContextEvent sce );  // ServletContext启动时触发    public void contextDestroyed ( ServletContextEvent sce );    // ServletContext销毁时触发

Spring IOC启动

spring ioc容器初始化具体代码如下：

org.springframework.web.context.ContextLoaderListenerpublic void contextInitialized(ServletContextEvent event) {this.contextLoader = createContextLoader();if (this.contextLoader == null) {this.contextLoader = this;}// 对spring ioc容器进行初始化this.contextLoader.initWebApplicationContext(event.getServletContext());}

IOC容器的初始化是由ContextLoader类执行：

org.springframework.web.context.ContextLoaderpublic WebApplicationContext initWebApplicationContext(ServletContext servletContext) {// 是否已经加载IOC容器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);}if (this.context instanceof ConfigurableWebApplicationContext) {ConfigurableWebApplicationContext cwac = (ConfigurableWebApplicationContext) this.context;if (!cwac.isActive()) {// The context has not yet been refreshed -> provide services such as// setting the parent context, setting the application context id, etcif (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);cwac.setParent(parent);}// 此方法是刷新初始化IOC容器的地方configureAndRefreshWebApplicationContext(cwac, servletContext);}}// IOC容器加载后，将IOC容器保存于ServletContext容器中servletContext.setAttribute(WebApplicationContext.ROOT_WEB_APPLICATION_CONTEXT_ATTRIBUTE, this.context);...}

熟悉的refresh()方法的调用：

org.springframework.web.context.ContextLoader  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 informationString idParam = sc.getInitParameter(CONTEXT_ID_PARAM);if (idParam != null) {wac.setId(idParam);}else {// Generate default id...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 {wac.setId(ConfigurableWebApplicationContext.APPLICATION_CONTEXT_ID_PREFIX +ObjectUtils.getDisplayString(sc.getContextPath()));}}}wac.setServletContext(sc);String initParameter = sc.getInitParameter(CONFIG_LOCATION_PARAM);if (initParameter != null) {wac.setConfigLocation(initParameter);}customizeContext(sc, wac);// 熟悉的refresh()对Spring IOC容器进行加载，接下来的步骤就是 "自我分析-Spring IOC"文脏中的内容wac.refresh();}

Spring IOC销毁

对Spring IOC容器和其他Spring环境信息进行销毁：

org.springframework.web.context.ContextLoaderListenerpublic void contextDestroyed(ServletContextEvent event) {if (this.contextLoader != null) {this.contextLoader.closeWebApplicationContext(event.getServletContext());}ContextCleanupListener.cleanupAttributes(event.getServletContext());}

具体清理销毁了spring的什么东西，自己再跟踪下代码即可。

若文中存在分析错误，望留言指出，在此非常感谢。