spring学习过程

容器启动的时候读取web.xml文件
有spring 启动配置

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

找到ContextLoaderListener类
ContextLoaderListener继承ContextLoader 实现ServletContextListener接口
ContextLoader 方法里有加载xml文件的方法，ServletContextListener接口是servlet-api.jar里的接口

public abstract interface ServletContextListener  extends EventListener{  public abstract void contextInitialized(ServletContextEvent paramServletContextEvent);  public abstract void contextDestroyed(ServletContextEvent paramServletContextEvent);}

EventListener类是空的，应该是个监听事件
ServletContextListener接口大致应该是监听容器启动事件
好，返回主要问题上
在 ContextLoaderListener类里有下面这个方法

/**     * Initialize the root web application context.     * 初始化一个context     * 怎么调用如果有大神知道请告诉一下     */    @Override    public void contextInitialized(ServletContextEvent event) {    //方法在ContextLoader类里        initWebApplicationContext(event.getServletContext());    }

public WebApplicationContext initWebApplicationContext(ServletContext servletContext) {//这里判断一下web应用是否已经有spring容器启动//如果有被加载过，将抛出异常。提示是否放置了多个ContextLoaderListener。        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.            //下面这句是创建WebApplicationContext的主过程。            if (this.context == null) {                this.context = createWebApplicationContext(servletContext);            }    //如果当前的应用上下文对象是 ConfigurableWebApplicationContext              if (this.context instanceof ConfigurableWebApplicationContext) {            //强制类型转换                ConfigurableWebApplicationContext cwac = (ConfigurableWebApplicationContext) this.context;                 // 如果应用上下文没有生效                  if (!cwac.isActive()) {                    // The context has not yet been refreshed -> provide services such as                    // setting the parent context, setting the application context id, etc                    // 如果该上下文对象为null                      if (cwac.getParent() == null) {                        // The context instance was injected without an explicit parent ->                        // determine parent for root web application context, if any.                        //加载父上下文                          ApplicationContext parent = loadParentContext(servletContext);                        // 设置父上下文                         cwac.setParent(parent);                    }                    configureAndRefreshWebApplicationContext(cwac, servletContext);                }            }//创建完的context置于servletContext中,//这样Spring容器的宿主就是ServletContext            servletContext.setAttribute(WebApplicationContext.ROOT_WEB_APPLICATION_CONTEXT_ATTRIBUTE, this.context);            ////获取当前线程的类加载器            ClassLoader ccl = Thread.currentThread().getContextClassLoader();            // 如果ContextLoader的类加载器和当前线程的类加载器一样，则应用上下文对象赋值给currentContext              if (ccl == ContextLoader.class.getClassLoader()) {                currentContext = this.context;            }            else if (ccl != null) {                currentContextPerThread.put(ccl, this.context);            }            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");                }                 // 返回应用上下文对象             return this.context;        }        catch (RuntimeException ex) {            logger.error("Context initialization failed", ex);            servletContext.setAttribute(WebApplicationContext.ROOT_WEB_APPLICATION_CONTEXT_ATTRIBUTE, ex);            throw ex;        }        catch (Error err) {            logger.error("Context initialization failed", err);            servletContext.setAttribute(WebApplicationContext.ROOT_WEB_APPLICATION_CONTEXT_ATTRIBUTE, err);            throw err;        }    }