springmvc 之DispatcherServlet初始化

ContextLoaderListener 只是辅助功能，用于创建WebApplicationContext类型实例，真正的逻辑实现其实在DispatcherServlet中进行，DispatcherServlet实现了servlet。servlet的生命周期是由servlet容器控制。分为3个阶段：初始化、运行、销毁

DispatcherServlet的初始化
在父类HttpServletBean中找到该方法

@Override    public final void init() throws ServletException {        if (logger.isDebugEnabled()) {            logger.debug("Initializing servlet '" + getServletName() + "'");        }        try {        // 解析init-param并封装到pvs中            PropertyValues pvs = new ServletConfigPropertyValues(getServletConfig(), this.requiredProperties);        //将当前servlet转为BeanWrapper,从而能够以Spring的方式来对init-param的值进行注入              BeanWrapper bw = PropertyAccessorFactory.forBeanPropertyAccess(this);            ResourceLoader resourceLoader = new ServletContextResourceLoader(getServletContext());            //注册自定义属性编辑器，一旦遇到Resouce类型的属性将会使用ResourceEditor进行解析            bw.registerCustomEditor(Resource.class, new ResourceEditor(resourceLoader, getEnvironment()));            //模版设计模式，留给子类覆盖            initBeanWrapper(bw);            bw.setPropertyValues(pvs, true);        }        catch (BeansException ex) {            logger.error("Failed to set bean properties on servlet '" + getServletName() + "'", ex);            throw ex;        }        //留给子类扩展        initServletBean();        if (logger.isDebugEnabled()) {            logger.debug("Servlet '" + getServletName() + "' configured successfully");        }    }

servletBean的初始化
在ContextloaderListener加载的时候已经创建了WebApplicationContext实例，而在这个方法中最重要的就是对这个实例进行进一步的补充初始化。
父类FrameworkSerlvet覆盖了HttpServletBean中的initServletBean函数。

@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 {            this.webApplicationContext = initWebApplicationContext();            //设计子类覆盖            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");        }    }

initWebApplicationContext方法的主要工作就是创建或者刷新WebApplicationContext实例并对servlet功能所使用的变量进行初始化。

protected WebApplicationContext initWebApplicationContext() {        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()) {                    // 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 -> set                        // the root application context (if any; may be null) as the parent                        cwac.setParent(rootContext);                    }    //刷新上下文环境               configureAndRefreshWebApplicationContext(cwac);                }            }        }        if (wac == null) {            // No context instance was injected at construction time -> see if one            // has been registered in the servlet context. If one exists, it is assumed            // that the parent context (if any) has already been set and that the            // user has performed any initialization such as setting the context id            //根据contextAttribute属性加载WebApplicationContext            wac = findWebApplicationContext();        }        if (wac == null) {            // 通过以上2种方式没有找到，只能这里重新创建新的实例            wac = createWebApplicationContext(rootContext);        }        if (!this.refreshEventReceived) {            // Either the context is not a ConfigurableApplicationContext with refresh            // support or the context injected at construction time had already been            // refreshed -> trigger initial onRefresh manually here.            onRefresh(wac);        }        if (this.publishContext) {            // Publish the context as a servlet context attribute.            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) {//获取servlet的初始化参数Contextclass，如果没有配置 默认为XmlWebApplicationContext        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");        }//通过反射方式实例化contextClass             ConfigurableWebApplicationContext wac =                (ConfigurableWebApplicationContext) BeanUtils.instantiateClass(contextClass);        wac.setEnvironment(getEnvironment());        //parent为在ContextLoaderListener中创建的WebApplicationContext实例        wac.setParent(parent);        wac.setConfigLocation(getContextConfigLocation());        //初始化spring环境包括加载配置文件        configureAndRefreshWebApplicationContext(wac);        return wac;    }

configureAndRefreshWebApplicationContext

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 information            if (this.contextId != null) {                wac.setId(this.contextId);            }            else {                // Generate default id...                wac.setId(ConfigurableWebApplicationContext.APPLICATION_CONTEXT_ID_PREFIX +                        ObjectUtils.getDisplayString(getServletContext().getContextPath()) + "/" + getServletName());            }        }        wac.setServletContext(getServletContext());        wac.setServletConfig(getServletConfig());        wac.setNamespace(getNamespace());        wac.addApplicationListener(new SourceFilteringListener(wac, new ContextRefreshListener()));        // The wac environment's #initPropertySources will be called in any case when the context        // is refreshed; do it eagerly here to ensure servlet property sources are in place for        // use in any post-processing or initialization that occurs below prior to #refresh        ConfigurableEnvironment env = wac.getEnvironment();        if (env instanceof ConfigurableWebEnvironment) {            ((ConfigurableWebEnvironment) env).initPropertySources(getServletContext(), getServletConfig());        }        postProcessWebApplicationContext(wac);        applyInitializers(wac);        wac.refresh();    }

AbstractApplicationContext提供的refresh方法。

@Override    public void refresh() throws BeansException, IllegalStateException {        synchronized (this.startupShutdownMonitor) {            // Prepare this context for refreshing.            prepareRefresh();            // Tell the subclass to refresh the internal bean factory.            ConfigurableListableBeanFactory beanFactory = obtainFreshBeanFactory();            // Prepare the bean factory for use in this context.            prepareBeanFactory(beanFactory);            try {                // Allows post-processing of the bean factory in context subclasses.                postProcessBeanFactory(beanFactory);                // Invoke factory processors registered as beans in the context.                invokeBeanFactoryPostProcessors(beanFactory);                // Register bean processors that intercept bean creation.                registerBeanPostProcessors(beanFactory);                // Initialize message source for this context.                initMessageSource();                // Initialize event multicaster for this context.                initApplicationEventMulticaster();                // Initialize other special beans in specific context subclasses.                onRefresh();                // Check for listener beans and register them.                registerListeners();                // Instantiate all remaining (non-lazy-init) singletons.                finishBeanFactoryInitialization(beanFactory);                // Last step: publish corresponding event.                finishRefresh();            }            catch (BeansException ex) {                logger.warn("Exception encountered during context initialization - cancelling refresh attempt", ex);                // Destroy already created singletons to avoid dangling resources.                destroyBeans();                // Reset 'active' flag.                cancelRefresh(ex);                // Propagate exception to caller.                throw ex;            }            finally {                // Reset common introspection caches in Spring's core, since we                // might not ever need metadata for singleton beans anymore...                resetCommonCaches();            }        }    }

继续看initWebApplicationContext方法调用DispatcherServlet类 onRefresh(wac)。

@Override    protected void onRefresh(ApplicationContext context) {        initStrategies(context);    }    //一套完整的springmvc 配置属性    protected void initStrategies(ApplicationContext context) {        //初始化MultipartResolver        initMultipartResolver(context);        //初始化LocaleResolver        initLocaleResolver(context);        //初始化ThemeResolver        initThemeResolver(context);        //初始化HandlerMappings ：注册了 RequestMappingHandlerMapping和BeanNameUrlHandlerMapping         initHandlerMappings(context);        //初始化HandlerAdapters 注册了 RequestMappingHandlerAdapter、HttpRequestHandlerAdapter和SimpleControllerHandlerAdapter        initHandlerAdapters(context);        //初始化HandlerExceptionResolvers        initHandlerExceptionResolvers(context);        //初始化RequestToViewNameTranslator        initRequestToViewNameTranslator(context);        //初始化ViewResolvers        initViewResolvers(context);        //初始化FlashMapManager        initFlashMapManager(context);    }