从源码角度看springmvc的请求处理过程
在分析spring mvc源码之前,先看一张图:
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请求处理的过程:
1.DispatcherServelt作为前端控制器,拦截request对象。
2.DispatcherServlet接收到request对象之后,查询HandlerMapping,得到一个HandlerExecutionChain对象。
3.DispatcherServlet将Handler对象交由HandlerAdapter(适配器模式的典型应用),调用相应的controller方法。
4.Controller方法返回ModelAndView对象,DispatcherServlet将view交由ViewResolver进行解析,得到相应的视图。用model渲染视图。
5.返回响应结果。
整个过程的流程其实就是DispatcherServelt中doDispatch()方法的调用过程。
protected void doDispatch(HttpServletRequest request, HttpServletResponse response) throws Exception { //第一步拦截request对象,doDispatch()方法在doService()方法中被调用,request对象是经过处理的。 HttpServletRequest processedRequest = request; HandlerExecutionChain mappedHandler = null; boolean multipartRequestParsed = false; WebAsyncManager asyncManager = WebAsyncUtils.getAsyncManager(request); try { ModelAndView mv = null; Exception dispatchException = null; try { //和文件的上传和下载有关系,判断请求的类型是否是multipart类型 processedRequest = checkMultipart(request); multipartRequestParsed = (processedRequest != request); // Determine handler for the current request. //主要看这里,这里是得到HandlerExecutionChain的方法。关于Handler()方法向下看 mappedHandler = getHandler(processedRequest); if (mappedHandler == null || mappedHandler.getHandler() == null) { noHandlerFound(processedRequest, response); return; } // Determine handler adapter for the current request. //这里已经获取到HandlerExecutionChain对象,接下来就要获取HandlerAdapter对象,调用Handler对象的方法。 HandlerAdapter ha = getHandlerAdapter(mappedHandler.getHandler()); // Process last-modified header, if supported by the handler //有关浏览器缓存的设定(304) 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; } } //pan'du if (!mappedHandler.applyPreHandle(processedRequest, response)) { return; } // Actually invoke the handler. mv = ha.handle(processedRequest, response, mappedHandler.getHandler()); if (asyncManager.isConcurrentHandlingStarted()) { return; } //解析视图,数据渲染 applyDefaultViewName(request, 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()) { // 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); } } } } protected HandlerExecutionChain getHandler(HttpServletRequest request) throws Exception { //遍历HandlerMappingList对象(存储若干个HandlerMapping对象),不断调用,直到不为空为止,否则返回null for (HandlerMapping hm : this.handlerMappings) { if (logger.isTraceEnabled()) { logger.trace( "Testing handler map [" + hm + "] in DispatcherServlet with name '" + getServletName() + "'"); } HandlerExecutionChain handler = hm.getHandler(request); if (handler != null) { return handler; } } return null; }
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