这一次搞懂Spring Web零xml配置原理以及父子容器关系 (3)

可以看到就是创建了一个AnnotationConfigWebApplicationContext对象，并将我们的配置类SpringContainer注册了进去。接着创建Tomcat启动加载监听器ContextLoaderListener，该监听器有一个contextInitialized方法，会在Tomcat启动时调用。

public void contextInitialized(ServletContextEvent event) { initWebApplicationContext(event.getServletContext()); } */ public WebApplicationContext initWebApplicationContext(ServletContext servletContext) { 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, 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); cwac.setParent(parent); } configureAndRefreshWebApplicationContext(cwac, servletContext); } } servletContext.setAttribute(WebApplicationContext.ROOT_WEB_APPLICATION_CONTEXT_ATTRIBUTE, this.context); ClassLoader ccl = Thread.currentThread().getContextClassLoader(); if (ccl == ContextLoader.class.getClassLoader()) { currentContext = this.context; } else if (ccl != null) { currentContextPerThread.put(ccl, this.context); } return this.context; } }

可以看到就是去初始化容器，这个和之前分析xml解析是一样的，主要注意这里封装了ServletContext对象，并将父容器设置到了该对象中。
父容器创建完成后自然就是子容器的创建，来到registerDispatcherServlet方法：

protected void registerDispatcherServlet(ServletContext servletContext) { String servletName = getServletName(); Assert.hasLength(servletName, "getServletName() must not return null or empty"); //创建springmvc的上下文，注册了MvcContainer类 WebApplicationContext servletAppContext = createServletApplicationContext(); Assert.notNull(servletAppContext, "createServletApplicationContext() must not return null"); //创建DispatcherServlet FrameworkServlet dispatcherServlet = createDispatcherServlet(servletAppContext); Assert.notNull(dispatcherServlet, "createDispatcherServlet(WebApplicationContext) must not return null"); dispatcherServlet.setContextInitializers(getServletApplicationContextInitializers()); ServletRegistration.Dynamic registration = servletContext.addServlet(servletName, dispatcherServlet); if (registration == null) { throw new IllegalStateException("Failed to register servlet with name '" + servletName + "'. " + "Check if there is another servlet registered under the same name."); } /* * 如果该元素的值为负数或者没有设置，则容器会当Servlet被请求时再加载。 如果值为正整数或者0时，表示容器在应用启动时就加载并初始化这个servlet， 值越小，servlet的优先级越高，就越先被加载 * */ registration.setLoadOnStartup(1); registration.addMapping(getServletMappings()); registration.setAsyncSupported(isAsyncSupported()); Filter[] filters = getServletFilters(); if (!ObjectUtils.isEmpty(filters)) { for (Filter filter : filters) { registerServletFilter(servletContext, filter); } } customizeRegistration(registration); } protected WebApplicationContext createServletApplicationContext() { AnnotationConfigWebApplicationContext context = new AnnotationConfigWebApplicationContext(); Class<?>[] configClasses = getServletConfigClasses(); if (!ObjectUtils.isEmpty(configClasses)) { context.register(configClasses); } return context; }

这里也是创建了一个AnnotationConfigWebApplicationContext对象，不同的只是这里注册的配置类就是我们的Servlet配置了。然后创建了DispatcherServlet对象，并将上下文对象设置了进去。看到这你可能会疑惑，既然父子容器创建的都是相同类的对象，何来的父子容器之说？别急，这个在初始化该上文时就明白了。但是这里的初始化入口在哪呢？没有看到任何监听器的创建和调用。实际上这里的上下文对象初始化是在Servlet初始化时实现的，即init方法，直接来到HttpServletBean的init方法（分析SpringMVC源码时讲过）：

public final void init() throws ServletException { ...省略 // Let subclasses do whatever initialization they like. initServletBean(); } protected final void initServletBean() throws ServletException { try { this.webApplicationContext = initWebApplicationContext(); initFrameworkServlet(); } } protected WebApplicationContext initWebApplicationContext() { //这里会从servletContext中获取到父容器，就是通过监听器加载的容器 WebApplicationContext rootContext = WebApplicationContextUtils.getWebApplicationContext(getServletContext()); WebApplicationContext wac = null; if (this.webApplicationContext != null) { // A context instance was injected at construction time -> use it wac = this.webApplicationContext; if (wac instanceof ConfigurableWebApplicationContext) { ConfigurableWebApplicationContext cwac = (ConfigurableWebApplicationContext) wac; if (!cwac.isActive()) { if (cwac.getParent() == null) { cwac.setParent(rootContext); } //容器加载 configureAndRefreshWebApplicationContext(cwac); } } } if (wac == null) { wac = findWebApplicationContext(); } if (wac == null) { wac = createWebApplicationContext(rootContext); } if (!this.refreshEventReceived) { synchronized (this.onRefreshMonitor) { onRefresh(wac); } } if (this.publishContext) { // Publish the context as a servlet context attribute. String attrName = getServletContextAttributeName(); getServletContext().setAttribute(attrName, wac); } return wac; }