springMvc的执行流程(源码分析)
1.在springMvc中负责处理请求的类为DispatcherServlet,这个类与我们传统的Servlet是一样的。我们来看看它的继承图
2. 我们发现DispatcherServlet也继承了HttpServlet,所以DispatcherServlet在处理请求时也会从service()方法开始。知道这一点后我们开始分析它的处理过程。
(1).我们在ApplicationFilterChain中的internalDoFilter()方法中打断点(至于为什么从这儿开始,需要去看Tomcat)
private void internalDoFilter(ServletRequest request,ServletResponse response)throws IOException, ServletException {// Call the next filter if there is oneif (pos < n) {ApplicationFilterConfig filterConfig = filters[pos++];try {Filter filter = filterConfig.getFilter();if (request.isAsyncSupported() && "false".equalsIgnoreCase(filterConfig.getFilterDef().getAsyncSupported())) {request.setAttribute(Globals.ASYNC_SUPPORTED_ATTR, Boolean.FALSE);}if( Globals.IS_SECURITY_ENABLED ) {final ServletRequest req = request;final ServletResponse res = response;Principal principal =((HttpServletRequest) req).getUserPrincipal();Object[] args = new Object[]{req, res, this};SecurityUtil.doAsPrivilege ("doFilter", filter, classType, args, principal);} else {filter.doFilter(request, response, this);}} catch (IOException | ServletException | RuntimeException e) {throw e;} catch (Throwable e) {e = ExceptionUtils.unwrapInvocationTargetException(e);ExceptionUtils.handleThrowable(e);throw new ServletException(sm.getString("filterChain.filter"), e);}return;}// We fell off the end of the chain -- call the servlet instancetry {if (ApplicationDispatcher.WRAP_SAME_OBJECT) {lastServicedRequest.set(request);lastServicedResponse.set(response);}if (request.isAsyncSupported() && !servletSupportsAsync) {request.setAttribute(Globals.ASYNC_SUPPORTED_ATTR,Boolean.FALSE);}// Use potentially wrapped request from this pointif ((request instanceof HttpServletRequest) &&(response instanceof HttpServletResponse) &&Globals.IS_SECURITY_ENABLED ) {final ServletRequest req = request;final ServletResponse res = response;Principal principal =((HttpServletRequest) req).getUserPrincipal();Object[] args = new Object[]{req, res};SecurityUtil.doAsPrivilege("service",servlet,classTypeUsedInService,args,principal);} else {servlet.service(request, response); //在这里打断点,进入到我们的service方法}} catch (IOException | ServletException | RuntimeException e) {throw e;} catch (Throwable e) {e = ExceptionUtils.unwrapInvocationTargetException(e);ExceptionUtils.handleThrowable(e);throw new ServletException(sm.getString("filterChain.servlet"), e);} finally {if (ApplicationDispatcher.WRAP_SAME_OBJECT) {lastServicedRequest.set(null);lastServicedResponse.set(null);}}}
(2)进入到FrameworkServlet中的service方法(注意在FrameworkServlet中重写了HttpServlet中的service方法)
@Overrideprotected void service(HttpServletRequest request, HttpServletResponse response)throws ServletException, IOException {HttpMethod httpMethod = HttpMethod.resolve(request.getMethod()); //HttpMethod为枚举类型,成员为GET, HEAD, POST, PUT, PATCH, DELETE, OPTIONS, TRACE;if (HttpMethod.PATCH == httpMethod || httpMethod == null) { //如果请求方法为空,或者是PATCHprocessRequest(request, response); //处理请求}else {super.service(request, response); //交给父类进行处理,本例中我们是get请求,所以转到这里}}
(3)进入到父类HttpServlet中的service方法
protected void service(HttpServletRequest req, HttpServletResponse resp)throws ServletException, IOException {String method = req.getMethod(); //获取请求的方法if (method.equals(METHOD_GET)) {long lastModified = getLastModified(req);if (lastModified == -1) {// servlet doesn't support if-modified-since, no reason// to go through further expensive logic doGet(req, resp); //执行get请求} else {long ifModifiedSince;try {ifModifiedSince = req.getDateHeader(HEADER_IFMODSINCE);} catch (IllegalArgumentException iae) {// Invalid date header - proceed as if none was setifModifiedSince = -1;}if (ifModifiedSince < (lastModified / 1000 * 1000)) {// If the servlet mod time is later, call doGet()// Round down to the nearest second for a proper compare// A ifModifiedSince of -1 will always be less maybeSetLastModified(resp, lastModified);doGet(req, resp);} else {resp.setStatus(HttpServletResponse.SC_NOT_MODIFIED);}}} else if (method.equals(METHOD_HEAD)) {long lastModified = getLastModified(req);maybeSetLastModified(resp, lastModified);doHead(req, resp);} else if (method.equals(METHOD_POST)) {doPost(req, resp);} else if (method.equals(METHOD_PUT)) {doPut(req, resp);} else if (method.equals(METHOD_DELETE)) {doDelete(req, resp);} else if (method.equals(METHOD_OPTIONS)) {doOptions(req,resp);} else if (method.equals(METHOD_TRACE)) {doTrace(req,resp);} else {//// Note that this means NO servlet supports whatever// method was requested, anywhere on this server.// String errMsg = lStrings.getString("http.method_not_implemented");Object[] errArgs = new Object[1];errArgs[0] = method;errMsg = MessageFormat.format(errMsg, errArgs);resp.sendError(HttpServletResponse.SC_NOT_IMPLEMENTED, errMsg);}}
(4)由于doGet方法也被我们的FrameworkServlet重写,所以这里转向FrameworkServlet类
@Overrideprotected final void doGet(HttpServletRequest request, HttpServletResponse response)throws ServletException, IOException {processRequest(request, response); //我们在这里发现最终还是会到达processRequest方法}
(4)我们来看看FrameworkServlet中的processRequest方法
protected final void processRequest(HttpServletRequest request, HttpServletResponse response)throws ServletException, IOException {long startTime = System.currentTimeMillis(); //在本篇中只介绍大致的执行过程,这里不详细介绍。。。。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); //我们关心这个方法,发现它会转向doService方法 }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);}}
(5)FrameworkServlet中的doService方法(该方法为抽象方法,有自类具体实现) 所以processRequest为模板模式的实现
protected abstract void doService(HttpServletRequest request, HttpServletResponse response)throws Exception;
(6)我们看上面的类图,FrameworkServlet的自类为DispatcherServlet(饶了半天终于到了我们的DispatcherServlet)
@Overrideprotected 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) + "]");}// Keep a snapshot of the request attributes in case of an include,// to be able to restore the original attributes after the include.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(DEFAULT_STRATEGIES_PREFIX)) {attributesSnapshot.put(attrName, request.getAttribute(attrName));}}}// Make framework objects available to handlers and view objects. 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); //我们重点关注这个方法,进行调度}finally {if (!WebAsyncUtils.getAsyncManager(request).isConcurrentHandlingStarted()) {// Restore the original attribute snapshot, in case of an include.if (attributesSnapshot != null) {restoreAttributesAfterInclude(request, attributesSnapshot);}}}}
(7)我们发现最终的调度过程都是交个DispatcherServlet中的doDispatcher()方法来完成的,重点分析这个方法
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);// Determine handler for the current request.mappedHandler = getHandler(processedRequest); //获取HandlerExecutionChain,在HandlerExecutionChain中包含了我们的Controller以及拦截器if (mappedHandler == null || mappedHandler.getHandler() == null) {noHandlerFound(processedRequest, response);return; //如果找不到执行方法则退出}// Determine handler adapter for the current request.HandlerAdapter ha = getHandlerAdapter(mappedHandler.getHandler()); //通过我们的Handler来找到HandlerAdpter(处理器执行器)// Process last-modified header, if supported by the handler.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)) { //执行拦截器的preHadnle()方法return;}// Actually invoke the handler.mv = ha.handle(processedRequest, response, mappedHandler.getHandler()); //执行具体的Controller中的方法,得到一个ModelAndView对象if (asyncManager.isConcurrentHandlingStarted()) {return;}applyDefaultViewName(processedRequest, mv); mappedHandler.applyPostHandle(processedRequest, response, mv); //执行拦截器的postHandler方法}catch (Exception ex) {dispatchException = ex;}catch (Throwable err) {// As of 4.3, we're processing Errors thrown from handler methods as well,// making them available for @ExceptionHandler methods and other scenarios.dispatchException = new NestedServletException("Handler dispatch failed", err);}processDispatchResult(processedRequest, response, mappedHandler, mv, dispatchException); //在这里进行师徒解析的过程}catch (Exception ex) {triggerAfterCompletion(processedRequest, response, mappedHandler, ex);}catch (Throwable err) {triggerAfterCompletion(processedRequest, response, mappedHandler,new NestedServletException("Handler processing failed", err));}finally {if (asyncManager.isConcurrentHandlingStarted()) {// Instead of postHandle and afterCompletionif (mappedHandler != null) {mappedHandler.applyAfterConcurrentHandlingStarted(processedRequest, response);}}else {// Clean up any resources used by a multipart request.if (multipartRequestParsed) {cleanupMultipart(processedRequest);}}}}
这样DispatcherServlet的一次请求过程就完成了(当然这里只是粗略的解析了一下执行流程,之后再去看源码不断的细化)
转载于:https://www.cnblogs.com/liwangcai/p/10743943.html
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