Spring MVC入门(十四):DispatcherServlet调用组件处理请求
- 查看源码
# 查看DispatcherServlet类 protected void doDispatch(HttpServletRequest request, HttpServletResponse response) throws Exception { // 1.到发送的请求,并赋值给processedRequest HttpServletRequest processedRequest = request; // 2. 声明1个变量mappedHandler,该变量用于存储(控制器方法、拦截器集合、拦截器索引) 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); // 3.将processedRequest 中的数据赋值给mappedHandler if (mappedHandler == null) { noHandlerFound(processedRequest, response); return; } // Determine handler adapter for the current request. HandlerAdapter ha = getHandlerAdapter(mappedHandler.getHandler()); // 4.处理器适配器,找到controller,并调用对应的controller // 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 (new ServletWebRequest(request, response).checkNotModified(lastModified) && isGet) { return; } } if (!mappedHandler.applyPreHandle(processedRequest, response)) { // 5. 调用拦截器的PreHandle方法 return; } // Actually invoke the handler. mv = ha.handle(processedRequest, response, mappedHandler.getHandler()); // 6.处理器适配器,处理了对应的controller,获得1个modelandview对象 if (asyncManager.isConcurrentHandlingStarted()) { return; } applyDefaultViewName(processedRequest, mv); mappedHandler.applyPostHandle(processedRequest, response, mv); // 7.调用拦截器的PostHandle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); // 8. 渲染视图 } 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 afterCompletion if (mappedHandler != null) { mappedHandler.applyAfterConcurrentHandlingStarted(processedRequest, response); } } else { // Clean up any resources used by a multipart request. if (multipartRequestParsed) { cleanupMultipart(processedRequest); } } } } # 查看processDispatchResult方法,如果有异常时,渲染异常信息 private void processDispatchResult(HttpServletRequest request, HttpServletResponse response, @Nullable HandlerExecutionChain mappedHandler, @Nullable ModelAndView mv, @Nullable Exception exception) throws Exception { boolean errorView = false; if (exception != null) { if (exception instanceof ModelAndViewDefiningException) { logger.debug("ModelAndViewDefiningException encountered", exception); mv = ((ModelAndViewDefiningException) exception).getModelAndView(); } else { Object handler = (mappedHandler != null ? mappedHandler.getHandler() : null); mv = processHandlerException(request, response, handler, exception); errorView = (mv != null); } } // Did the handler return a view to render? if (mv != null && !mv.wasCleared()) { render(mv, request, response); if (errorView) { WebUtils.clearErrorRequestAttributes(request); } } else { if (logger.isTraceEnabled()) { logger.trace("No view rendering, null ModelAndView returned."); } } if (WebAsyncUtils.getAsyncManager(request).isConcurrentHandlingStarted()) { // Concurrent handling started during a forward return; } if (mappedHandler != null) { // Exception (if any) is already handled.. mappedHandler.triggerAfterCompletion(request, response, null); } } # 以上方法中渲染视图的代码 render(mv, request, response); # 最后执行拦截器中的AfterCompletion方法 mappedHandler.triggerAfterCompletion(request, response, null);
- springmvc执行流程
1)用户向服务器发送请求,请求被SpringMVC 前端控制器 DispatcherServlet捕获。 2) DispatcherServlet对请求URL进行解析,得到请求资源标识符(URI),判断请求URI对应的映射: a) 不存在 i. 再判断是否配置了mvc:default-servlet-handler ii. 如果没配置,则控制台报映射查找不到,客户端展示404错误 iii. 如果有配置,则访问目标资源(一般为静态资源,如:JS,CSS,HTML),找不到客户端也会展示404错误 b) 存在则执行下面的流程 3) 根据该URI,调用HandlerMapping获得该Handler配置的所有相关的对象(包括Handler对象以及Handler对象对应的拦截器),最后以HandlerExecutionChain执行链对象的形式返回。 4) DispatcherServlet 根据获得的Handler,选择一个合适的HandlerAdapter。 5) 如果成功获得HandlerAdapter,此时将开始执行拦截器的preHandler(…)方法【正向】 6) 提取Request中的模型数据,填充Handler入参,开始执行Handler(Controller)方法,处理请求 在填充Handler的入参过程中,根据你的配置,Spring将帮你做一些额外的工作: a) HttpMessageConveter: 将请求消息(如Json、xml等数据)转换成一个对象,将对象转换为指定的响应信息 b) 数据转换:对请求消息进行数据转换。如String转换成Integer、Double等 c) 数据格式化:对请求消息进行数据格式化。 如将字符串转换成格式化数字或格式化日期等 d) 数据验证: 验证数据的有效性(长度、格式等),验证结果存储到BindingResult或Error中 7) Handler执行完成后,向DispatcherServlet 返回一个ModelAndView对象。 8) 此时将开始执行拦截器的postHandle(...)方法【逆向】。 9) 根据返回的ModelAndView(此时会判断是否存在异常:如果存在异常,则执行HandlerExceptionResolver进行异常处理)选择一个适合的ViewResolver进行视图解析,根据Model和View,来渲染视图 10) 渲染视图完毕执行拦截器的afterCompletion(…)方法【逆向】 11) 将渲染结果返回给客户端
分类:
后端
标签:
Spring MVC
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