淺談Spring與SpringMVC父子容器的關系與初始化

 <context-param>
    <param-name>contextConfigLocation</param-name>//指定spring ioc配置文件的位置
    <param-value>classpath*:spring/*.xml</param-value>
  </context-param>
  <!-- Creates the Spring Container shared by all Servlets and Filters -->
  <listener>
    <listener-class>org.springframework.web.context.ContextLoaderListener</listener-class>
  </listener>
<!-- 配置DisaptcherServlet -->
  <servlet>
    <servlet-name>springMVC</servlet-name>
    <servlet-class>org.springframework.web.servlet.DispatcherServlet</servlet-class>
    <!-- 初始化參數，配置springmvc配置文件 -->
    <init-param>
      <param-name>contextConfigLocation</param-name>
      <param-value>springMVC配置文件的路徑</param-value>
    </init-param>
    <!-- web容器啟動時加載該Servlet -->
    <load-on-startup>1</load-on-startup>
  </servlet>
  <servlet-mapping>
    <servlet-name>springMVC</servlet-name>
    <url-pattern>/</url-pattern>
  </servlet-mapping>

/DispatcherServlet第一次加載時調用init方法
@Override
  public final void init() throws ServletException {
    if (logger.isDebugEnabled()) {
      logger.debug("Initializing servlet '" + getServletName() + "'");
    }
    // Set bean properties from init parameters.
    try {
/*加載web.xml文件中的servlet標簽中的init-param，其中含有springMVC的配置文件的名字和路徑
 *若沒有，則默認為（servlet-name）-servlet.xml，
 *默認路徑為WEF—INF下
 */
      PropertyValues pvs = new ServletConfigPropertyValues(getServletConfig(), this.requiredProperties);
     //創建BeanWrapper實例，為DispatcherServlet設置屬性
      BeanWrapper bw = PropertyAccessorFactory.forBeanPropertyAccess(this);
      ResourceLoader resourceLoader = new ServletContextResourceLoader(getServletContext());
      bw.registerCustomEditor(Resource.class, new ResourceEditor(resourceLoader, getEnvironment()));
      initBeanWrapper(bw);
     //把init-param中的參數設置到DispatcherServlet里面去
      bw.setPropertyValues(pvs, true);
    }
    catch (BeansException ex) {
      logger.error("Failed to set bean properties on servlet '" + getServletName() + "'", ex);
      throw ex;
    }
 
 
    // Let subclasses do whatever initialization they like.
    //該方法在FrameworkServlet中
    initServletBean();
 
 
    if (logger.isDebugEnabled()) {
      logger.debug("Servlet '" + getServletName() + "' configured successfully");
    }
  }

@Override
  protected final void initServletBean() throws ServletException {
    getServletContext().log("Initializing Spring FrameworkServlet '" + getServletName() + "'");
    if (this.logger.isInfoEnabled()) {
      this.logger.info("FrameworkServlet '" + getServletName() + "': initialization started");
    }
    long startTime = System.currentTimeMillis();
 
    try {
      //創建springmvc的ioc容器實例
      this.webApplicationContext = initWebApplicationContext();
      initFrameworkServlet();
    }
    catch (ServletException ex) {
      this.logger.error("Context initialization failed", ex);
      throw ex;
    }
    catch (RuntimeException ex) {
      this.logger.error("Context initialization failed", ex);
      throw ex;
    }
 
    if (this.logger.isInfoEnabled()) {
      long elapsedTime = System.currentTimeMillis() - startTime;
      this.logger.info("FrameworkServlet '" + getServletName() + "': initialization completed in " +
          elapsedTime + " ms");
    }
  }

protected WebApplicationContext initWebApplicationContext() {
    //首先通過ServletContext獲得spring容器，因為子容器springMVC要和父容器spring容器進行關聯
    //這就是為什么要在ServletContext中注冊spring ioc容器的原因
    WebApplicationContext rootContext =
        WebApplicationContextUtils.getWebApplicationContext(getServletContext());
    //定義springMVC容器wac
    WebApplicationContext wac = null;
 
 
    //判斷容器是否由編程式傳入（即是否已經存在了容器實例），存在的話直接賦值給wac，給springMVC容器設置父容器
    //最后調用刷新函數configureAndRefreshWebApplicationContext(wac)，作用是把springMVC的配置信息加載到容器中去（之前已經將配置信息的路徑設置到了bw中）
    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) {
            // The context instance was injected without an explicit parent -> set
            // the root application context (if any; may be null) as the parent
            //將spring ioc設置為springMVC ioc的父容器
            cwac.setParent(rootContext);
          }
 
 
          configureAndRefreshWebApplicationContext(cwac);
        }
      }
    }
    if (wac == null) {
      // 在ServletContext中尋找是否有springMVC容器，初次運行是沒有的，springMVC初始化完畢ServletContext就有了springMVC容器
      wac = findWebApplicationContext();
    }
 
 
    //當wac既沒有沒被編程式注冊到容器中的，也沒在ServletContext找得到，此時就要新建一個springMVC容器
    if (wac == null) {
      // 創建springMVC容器
      wac = createWebApplicationContext(rootContext);
    }
 
 
    if (!this.refreshEventReceived) {
      //到這里mvc的容器已經創建完畢，接著才是真正調用DispatcherServlet的初始化方法onRefresh(wac)
      onRefresh(wac);
    }
 
 
    if (this.publishContext) {
      //將springMVC容器存放到ServletContext中去，方便下次取出來
      String attrName = getServletContextAttributeName();
      getServletContext().setAttribute(attrName, wac);
      if (this.logger.isDebugEnabled()) {
        this.logger.debug("Published WebApplicationContext of servlet '" + getServletName() +
            "' as ServletContext attribute with name [" + attrName + "]");
      }
    }
    return wac;
  }

protected WebApplicationContext createWebApplicationContext(ApplicationContext parent) {
    Class<?> contextClass = getContextClass();
    if (this.logger.isDebugEnabled()) {
      this.logger.debug("Servlet with name '" + getServletName() +
          "' will try to create custom WebApplicationContext context of class '" +
          contextClass.getName() + "'" + ", using parent context [" + parent + "]");
    }
    if (!ConfigurableWebApplicationContext.class.isAssignableFrom(contextClass)) {
      throw new ApplicationContextException(
          "Fatal initialization error in servlet with name '" + getServletName() +
          "': custom WebApplicationContext class [" + contextClass.getName() +
          "] is not of type ConfigurableWebApplicationContext");
    }
    //實例化空白的ioc容器
    ConfigurableWebApplicationContext wac =
        (ConfigurableWebApplicationContext) BeanUtils.instantiateClass(contextClass);
    //給容器設置環境
    wac.setEnvironment(getEnvironment());
    //給容器設置父容器(就是spring容器)，兩個ioc容器關聯在一起了
    wac.setParent(parent);
    //給容器加載springMVC的配置信息，之前已經通過bw將配置文件路徑寫入到了DispatcherServlet中
    wac.setConfigLocation(getContextConfigLocation());
    //上面提到過這方法，刷新容器，根據springMVC配置文件完成初始化操作，此時springMVC容器創建完成
    configureAndRefreshWebApplicationContext(wac);
 
    return wac;
  }

@Override
  protected void onRefresh(ApplicationContext context) {
    initStrategies(context);
  }

protected void initStrategies(ApplicationContext context) {
    initMultipartResolver(context);//文件上傳解析
    initLocaleResolver(context);//本地解析
    initThemeResolver(context);//主題解析
    initHandlerMappings(context);//url請求映射
    initHandlerAdapters(context);//初始化真正調用controloler方法的類
    initHandlerExceptionResolvers(context);//異常解析
    initRequestToViewNameTranslator(context);
    initViewResolvers(context);//視圖解析
    initFlashMapManager(context);
  }