springMVC源码分析--DispatcherServlet请求获取及处理
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在之前的博客 springMVC源码分析--容器初始化(二)DispatcherServlet中我们介绍过DispatcherServlet,是在容器初始化过程中出现的,我们之前也说过DispatcherServlet其实就是一个HttpServlet,其实他是HttpServlet的子类,所以它和普通的HttpServlet有同样的配置:
- <span style="font-size:14px;"><span style="white-space:pre"> </span><servlet>
- <servlet-name>springmvc</servlet-name>
- <servlet-class>
- org.springframework.web.servlet.DispatcherServlet
- </servlet-class>
- <init-param>
- <param-name>contextConfigLocation</param-name>
- <param-value>classpath:springmvc-config.xml</param-value>
- </init-param>
- <load-on-startup>1</load-on-startup>
- </servlet>
-
- <servlet-mapping>
- <servlet-name>springmvc</servlet-name>
- <url-pattern>*.action</url-pattern>
- </servlet-mapping></span>
仅仅把DispatcherServlet当做一个Servlet的话,上面配置的含义就是这个Servlet会被所有的*.action的请求所调用。既然DispatcherServlet是一个HttpServlet那么它应该会实现HttpServlet提供的如下方法:
当然这些所有的方法的实现是DispatcherServlet的父类FrameworkServlet中实现的。
当然这些实现方法中的默认实现其实是如下的
FrameworkServlet类中
- @Override
- protected final void doPost(HttpServletRequest request, HttpServletResponse response)
- throws ServletException, IOException {
-
- processRequest(request, response);
- }
- @Override
- protected final void doGet(HttpServletRequest request, HttpServletResponse response)
- throws ServletException, IOException {
-
- processRequest(request, response);
- }
processRequest的实现是在FrameworkServlet中,此方法中最主要的操作就是调用doService方法- protected final void processRequest(HttpServletRequest request, HttpServletResponse response)
- throws ServletException, IOException {
-
- long startTime = System.currentTimeMillis();
- Throwable failureCause = null;
-
- LocaleContext previousLocaleContext = LocaleContextHolder.getLocaleContext();
- LocaleContext localeContext = buildLocaleContext(request);
-
- RequestAttributes previousAttributes = RequestContextHolder.getRequestAttributes();
- ServletRequestAttributes requestAttributes = buildRequestAttributes(request, response, previousAttributes);
-
- WebAsyncManager asyncManager = WebAsyncUtils.getAsyncManager(request);
- asyncManager.registerCallableInterceptor(FrameworkServlet.class.getName(), new RequestBindingInterceptor());
-
- initContextHolders(request, localeContext, requestAttributes);
-
- try {
- doService(request, response);
- }
- catch (ServletException ex) {
- failureCause = ex;
- throw ex;
- }
- catch (IOException ex) {
- failureCause = ex;
- throw ex;
- }
- catch (Throwable ex) {
- failureCause = ex;
- throw new NestedServletException("Request processing failed", ex);
- }
-
- finally {
- resetContextHolders(request, previousLocaleContext, previousAttributes);
- if (requestAttributes != null) {
- requestAttributes.requestCompleted();
- }
-
- if (logger.isDebugEnabled()) {
- if (failureCause != null) {
- this.logger.debug("Could not complete request", failureCause);
- }
- else {
- if (asyncManager.isConcurrentHandlingStarted()) {
- logger.debug("Leaving response open for concurrent processing");
- }
- else {
- this.logger.debug("Successfully completed request");
- }
- }
- }
-
- publishRequestHandledEvent(request, response, startTime, failureCause);
- }
- }
doService方法的最终实现是在DispatcherServlet中,这样所有的Http请求(GET、POST、PUT和DELETE等)的最终操作就DispatcherServlet中实现了。DispatcherServlet中doService的实现如下,对Request设置了一些全局属性,最终接下来的操作是在doDispatcher函数中实现了。
-
- @Override
- protected void doService(HttpServletRequest request, HttpServletResponse response) throws Exception {
- if (logger.isDebugEnabled()) {
- String resumed = WebAsyncUtils.getAsyncManager(request).hasConcurrentResult() ? " resumed" : "";
- logger.debug("DispatcherServlet with name '" + getServletName() + "'" + resumed +
- " processing " + request.getMethod() + " request for [" + getRequestUri(request) + "]");
- }
-
-
-
- Map<String, Object> attributesSnapshot = null;
- if (WebUtils.isIncludeRequest(request)) {
- attributesSnapshot = new HashMap<String, Object>();
- Enumeration<?> attrNames = request.getAttributeNames();
- while (attrNames.hasMoreElements()) {
- String attrName = (String) attrNames.nextElement();
- if (this.cleanupAfterInclude || attrName.startsWith("org.springframework.web.servlet")) {
- attributesSnapshot.put(attrName, request.getAttribute(attrName));
- }
- }
- }
-
-
-
- request.setAttribute(WEB_APPLICATION_CONTEXT_ATTRIBUTE, getWebApplicationContext());
-
- request.setAttribute(LOCALE_RESOLVER_ATTRIBUTE, this.localeResolver);
-
- request.setAttribute(THEME_RESOLVER_ATTRIBUTE, this.themeResolver);
-
- request.setAttribute(THEME_SOURCE_ATTRIBUTE, getThemeSource());
-
- FlashMap inputFlashMap = this.flashMapManager.retrieveAndUpdate(request, response);
- if (inputFlashMap != null) {
- request.setAttribute(INPUT_FLASH_MAP_ATTRIBUTE, Collections.unmodifiableMap(inputFlashMap));
- }
-
- request.setAttribute(OUTPUT_FLASH_MAP_ATTRIBUTE, new FlashMap());
-
- request.setAttribute(FLASH_MAP_MANAGER_ATTRIBUTE, this.flashMapManager);
-
- try {
- doDispatch(request, response);
- }
- finally {
- if (!WebAsyncUtils.getAsyncManager(request).isConcurrentHandlingStarted()) {
-
- if (attributesSnapshot != null) {
- restoreAttributesAfterInclude(request, attributesSnapshot);
- }
- }
- }
- }
doDispatch函数中完成了对一个请求的所有操作,包含的内容还是比较多的,我们就不做详细分解,接下来我们会一步一步的分析一个请求调用Controller的完整过程。
-
-
-
-
-
-
-
- protected void doDispatch(HttpServletRequest request, HttpServletResponse response) throws Exception {
-
- HttpServletRequest processedRequest = request;
- HandlerExecutionChain mappedHandler = null;
- boolean multipartRequestParsed = false;
-
- WebAsyncManager asyncManager = WebAsyncUtils.getAsyncManager(request);
-
- try {
- ModelAndView mv = null;
- Exception dispatchException = null;
-
- try {
-
- processedRequest = checkMultipart(request);
- multipartRequestParsed = (processedRequest != request);
-
-
- mappedHandler = getHandler(processedRequest);
- if (mappedHandler == null || mappedHandler.getHandler() == null) {
- noHandlerFound(processedRequest, response);
- return;
- }
-
-
-
- HandlerAdapter ha = getHandlerAdapter(mappedHandler.getHandler());
-
-
- String method = request.getMethod();
- boolean isGet = "GET".equals(method);
- if (isGet || "HEAD".equals(method)) {
- long lastModified = ha.getLastModified(request, mappedHandler.getHandler());
- if (logger.isDebugEnabled()) {
- logger.debug("Last-Modified value for [" + getRequestUri(request) + "] is: " + lastModified);
- }
- if (new ServletWebRequest(request, response).checkNotModified(lastModified) && isGet) {
- return;
- }
- }
-
- if (!mappedHandler.applyPreHandle(processedRequest, response)) {
- return;
- }
-
-
- mv = ha.handle(processedRequest, response, mappedHandler.getHandler());
-
- if (asyncManager.isConcurrentHandlingStarted()) {
- return;
- }
-
- applyDefaultViewName(processedRequest, mv);
-
- mappedHandler.applyPostHandle(processedRequest, response, mv);
- }
- catch (Exception ex) {
- dispatchException = ex;
- }
- processDispatchResult(processedRequest, response, mappedHandler, mv, dispatchException);
- }
- catch (Exception ex) {
- triggerAfterCompletion(processedRequest, response, mappedHandler, ex);
- }
- catch (Error err) {
- triggerAfterCompletionWithError(processedRequest, response, mappedHandler, err);
- }
- finally {
-
- if (asyncManager.isConcurrentHandlingStarted()) {
-
- if (mappedHandler != null) {
- mappedHandler.applyAfterConcurrentHandlingStarted(processedRequest, response);
- }
- }
- else {
-
-
- if (multipartRequestParsed) {
- cleanupMultipart(processedRequest);
- }
- }
- }
- }
调用完doDispatch之后就完成了一个请求的访问,其会将渲染后的页面或者数据返回给请求发起者。 0 0