这一次搞懂SpringMVC原理说明

这篇文章主要介绍了这一次搞懂SpringMVC原理说明，具有很好的参考价值，希望对大家有所帮助。一起跟随小编过来看看吧

前言

前面几篇文章，学习了Spring IOC、Bean实例化过程、AOP、事务的源码和设计思想，了解了Spring的整体运行流程，但如果是web开发，那么必不可少的还有Spring MVC，本篇主要分析在请求调用过程中SpringMVC的实现原理，通过本篇要搞懂它是怎么解决请求、参数、返回值映射等问题的。

正文

请求入口

我们都知道前端调用后端接口时，都会通过Servlet进行转发，而Servlet的声明周期包含下面四个阶段：

实例化（new）

初始化（init）

执行（service调用doGet/doPost）

销毁（destroy）

前两个阶段在Spring启动阶段就做好了（init根据配置可能是第一次请求时才会调用），销毁是服务关闭的时候进行，本文主要分析的就是请求执行阶段。我们知道SpringMVC的核心就是dispatcherServlet，该类是对Servlet的扩展，所以直接从该类的service方法开始，但在此类中没有service方法，那肯定是在其父类中，我们先来看看其继承体系：

逐个往上找，在FrameworkServlet方法中就有一个service方法：

protected void service(HttpServletRequest request, HttpServletResponse response) throws servletexception, IOException { HttpMethod httpMethod = HttpMethod.resolve(request.getmethod()); if (httpMethod == HttpMethod.PATCH || httpMethod == null) { processRequest(request, response); } else { super.service(request, response); } } protected void service(HttpServletRequest req, HttpServletResponse resp) throws servletexception, IOException { String method = req.getmethod(); if (method.equals(METHOD_GET)) { long lastModified = getLastModified(req); if (lastModified == -1) { doGet(req, resp); } else { long ifModifiedSince = req.getDateHeader(HEADER_IFMODSINCE); if (ifModifiedSince

但其主要还是调用父类HttpServlet中的方法，而该类又会根据不同的请求方式会调到子类中，最后的核心方法就是dispatcherServlet中的dodispatch方法：

protected void dodispatch(HttpServletRequest request, HttpServletResponse response) throws Exception { HttpServletRequest processedRequest = request; HandlerExecutionChain mappedHandler = null; boolean multipartRequestParsed = false; //异步管理 WebAsyncManager asyncManager = WebAsyncUtils.getAsyncManager(request); try { ModelAndView mv = null; Exception dispatchException = null; try { //文件上传 processedRequest = checkMultipart(request); multipartRequestParsed = (processedRequest != request); //这个方法很重要，重点看 // Determine handler for the current request. mappedHandler = getHandler(processedRequest); if (mappedHandler == null) { noHandlerFound(processedRequest, response); return; } //获取跟HandlerMethod匹配的HandlerAdapter对象 // Determine handler adapter for the current request. HandlerAdapter ha = getHandlerAdapter(mappedHandler.getHandler()); // 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; } } //前置过滤器，如果为false则直接返回 if (!mappedHandler.applyPreHandle(processedRequest, response)) { return; } //调用到Controller具体方法，核心方法调用，重点看看 // Actually invoke the handler. mv = ha.handle(processedRequest, response, mappedHandler.getHandler()); if (asyncManager.isConcurrentHandlingStarted()) { return; } applydefaultviewName(processedRequest, mv); //中置过滤器 mappedHandler.applyPostHandle(processedRequest, response, mv); } 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); } //视图渲染及后置过滤器执行 processdispatchResult(processedRequest, response, mappedHandler, mv, dispatchException); } 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上一篇：新手初学Java网络编程下一篇：Java中从键盘输入多个整数的方法热门搜索：