SpringMVC的初始化

springmvc的入口類爲dispatcherServlet,是一個標準的Servlet，在web.xml中配置

繼承關係以下

• HttpServlet
  • HttpServletBean
    • FrameworkServlet
      • DispatcherServlet

Servlet有兩大核心方法，init和service

涉及到初始化，確定是init，可是在DispatcherServlet中並無init方法，那必定是在父類中了，是的，在HttpServletBean中，簡要代碼以下

public final void init() throws ServletException {
    try {
        //初始化web.xml中配置的init-parms
        HttpServletBean.ServletConfigPropertyValues ex = new HttpServletBean.ServletConfigPropertyValues(this.getServletConfig(), this.requiredProperties);
        BeanWrapper bw = PropertyAccessorFactory.forBeanPropertyAccess(this);
        ServletContextResourceLoader resourceLoader = new ServletContextResourceLoader(this.getServletContext());
        bw.registerCustomEditor(Resource.class, new ResourceEditor(resourceLoader, this.getEnvironment()));
        this.initBeanWrapper(bw);
        bw.setPropertyValues(ex, true);
    } catch (BeansException var4) {
    }
    //提供擴展點，讓子類去實現，擴展初始化
    this.initServletBean();
}

在FrameworkServlet中，重寫了initServletBean方法，去掉枝節代碼，主幹以下

protected final void initServletBean() throws ServletException {
    try {
        //初始化servlet上下文
        this.webApplicationContext = this.initWebApplicationContext();
        //提供擴展點
        this.initFrameworkServlet();
    } catch (Exception var5) {
    }
}

//核心方法，初始化servlet上下文
protected WebApplicationContext initWebApplicationContext() {
    //經過ServletContext獲取根上下文：
    //servletContext.getAttribute("org.spring.framwork.web.context.webApplication.ROOT")
    WebApplicationContext rootContext = WebApplicationContextUtils.getWebApplicationContext(this.getServletContext());
    WebApplicationContext wac = null;
    if(this.webApplicationContext != null) {
        wac = this.webApplicationContext;
        if(wac instanceof ConfigurableWebApplicationContext) {
            ConfigurableWebApplicationContext attrName = (ConfigurableWebApplicationContext)wac;
            if(!attrName.isActive()) {
                if(attrName.getParent() == null) {
                    attrName.setParent(rootContext);
                }

                this.configureAndRefreshWebApplicationContext(attrName);
            }
        }
    }

    if(wac == null) {
        wac = this.findWebApplicationContext();
    }

    if(wac == null) {
        wac = this.createWebApplicationContext(rootContext);
    }

    if(!this.refreshEventReceived) {
        //提供擴展點，讓子類擴展初始化
        this.onRefresh(wac);
    }

    if(this.publishContext) {
        String attrName1 = this.getServletContextAttributeName();
        this.getServletContext().setAttribute(attrName1, wac);
    }

    return wac;
}

在DispatcherServlet中，重寫了onRefresh方法，onRefresh又委託initStrategies方法，擴展了各類SpringMVC的處理策略。

protected void initStrategies(ApplicationContext context) {
    this.initMultipartResolver(context);
    this.initLocaleResolver(context);
    this.initThemeResolver(context);
    this.initHandlerMappings(context);
    this.initHandlerAdapters(context);
    this.initHandlerExceptionResolvers(context);
    this.initRequestToViewNameTranslator(context);
    this.initViewResolvers(context);
    this.initFlashMapManager(context);
}

至此，初始化也就完畢了。總結一下，

• HttpServlet
  • HttpServletBean       --init()【初始化web.xml中的init-parms】
    • FrameworkServlet        --initServletBean()，調用initWebApplicationContext()方法
      • DispatcherServlet        --onRefresh()【初始化各類處理策略】

子類一直在擴展，來完善初始化的功能，這也是模版方法設計模式的應用，更加靈活