Spring Mvc结构解析

上图是Dispatcher Servlet的结构图，从图中可以清楚的看到Dispatcher Servlet的继承链，下面我们将基于Spring4.1.6揭开Spring MVC的神秘面纱。

初始化过程

我们都知道，Java中初始化顺序是：

1. 初始化父类静态变量(静态代码块，静态变量，静态方法，需要注意的是main方法也是静态的)
2. 初始化子类静态变量(范围同父类)
3. 初始化父类普通成员变量及方法
4. 调用父类构造方法
5. 初始化子类普通成员变量及方法
6. 调用子类构造方法

那么，在Dispatcher Servlet初始化的时候也是严格按照这个顺序来执行的。我们分别来看看在不同阶段都做了些什么。

HttpServletBean初始化过程关键代码

   @Overridepublic final void init() throws ServletException {//  从spring的配置文件中读取servlet的Init-Param。即spring配置文件路径等关键配置try {PropertyValues pvs = new ServletConfigPropertyValues(getServletConfig(), this.requiredProperties);BeanWrapper bw = PropertyAccessorFactory.forBeanPropertyAccess(this);ResourceLoader resourceLoader = new ServletContextResourceLoader(getServletContext());bw.registerCustomEditor(Resource.class, new ResourceEditor(resourceLoader, getEnvironment()));initBeanWrapper(bw);bw.setPropertyValues(pvs, true);}catch (BeansException ex) {logger.error("Failed to set bean properties on servlet '" + getServletName() + "'", ex);throw ex;}// 调用frameworkServlet的方法初始化initServletBean();}

FrameworkServlet初始化过程关键代码

    @Overrideprotected final void initServletBean() throws ServletException { this.webApplicationContext = initWebApplicationContext(); }protected WebApplicationContext initWebApplicationContext() {WebApplicationContext rootContext =WebApplicationContextUtils.getWebApplicationContext(getServletContext());WebApplicationContext wac = null;if (wac == null) {// 在这里初始化Spring MVC的context，并将Spring MVC的context和Servlet Context绑定wac = createWebApplicationContext(rootContext);}return wac;}protected WebApplicationContext createWebApplicationContext(ApplicationContext parent) {Class<?> contextClass = getContextClass();// 通过反射new一个空的context对象返回ConfigurableWebApplicationContext wac =(ConfigurableWebApplicationContext) BeanUtils.instantiateClass(contextClass);wac.setEnvironment(getEnvironment());wac.setParent(parent);wac.setConfigLocation(getContextConfigLocation());//  在这里会调用onRefreah方法，初始化Dispatcher Servlet的9大策略configureAndRefreshWebApplicationContext(wac);return wac;}protected void configureAndRefreshWebApplicationContext(ConfigurableWebApplicationContext wac) {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 informationif (this.contextId != null) {wac.setId(this.contextId);}else {wac.setId(ConfigurableWebApplicationContext.APPLICATION_CONTEXT_ID_PREFIX +ObjectUtils.getDisplayString(getServletContext().getContextPath()) + "/" + getServletName());}}// 为web application context设置基本属性wac.setServletContext(getServletContext());wac.setServletConfig(getServletConfig());wac.setNamespace(getNamespace());wac.addApplicationListener(new SourceFilteringListener(wac, new ContextRefreshListener()));ConfigurableEnvironment env = wac.getEnvironment();if (env instanceof ConfigurableWebEnvironment) {((ConfigurableWebEnvironment) env).initPropertySources(getServletContext(), getServletConfig());}postProcessWebApplicationContext(wac);applyInitializers(wac);// 关键，这里会刷新整个context，调用Dispatcher Servlet的onRefreah方法。初始化一系列Resolverswac.refresh();}

DispatcherServlet初始化过程关键代码

    /*** This implementation calls {@link #initStrategies}.*/@Overrideprotected void onRefresh(ApplicationContext context) {initStrategies(context);}/*** Initialize the strategy objects that this servlet uses.* <p>May be overridden in subclasses in order to initialize further strategy objects.*/protected void initStrategies(ApplicationContext context) {initMultipartResolver(context);initLocaleResolver(context);initThemeResolver(context);// 寻找配置的HandlerMapping，下篇文章我们会继续分析这里的详细过程。是url映射controller的关键，默认是RequestMappgingHandlerMapping和BeanNameUrlHandlerMapping，这些HandlerMapping会在spring context初始化的时候初始化。initHandlerMappings(context);// 寻找配置的适配器，默认是RequestMappingHandlerAdapter,HttpRequestHandlerAdapter,SimpleControllerHandlerAdapter这三种initHandlerAdapters(context);initHandlerExceptionResolvers(context);initRequestToViewNameTranslator(context);initViewResolvers(context);initFlashMapManager(context);}

从上面的关键部分代码可以看出Spring MVC在启动时的的大概流程，大致了解Spring MVC都做了什么。后续会继续分析请求到达Dispatcher Servlet后是如何找到对应的controller以及参数封装，最后再到数据返回等流程的详细过程。