SpringMVC工作原理源码分析

首先、当请求进入Tomcat时、在web.xml查找对应的Servlet类、找到DispatcherServlet类并且匹配路径 /、现在创建DispatcherServlet类的示例、并开始执行service方法、即Servlet类的初始方法、DispathcherServlet继承的父类通过调用service方法层层调用至DispatcherServlet类中的doService方法、在由doService方法调用doDispatch方法（核心流程在此方法中）

doDispatch

protected void doDispatch(HttpServletRequest request, HttpServletResponse response) throws Exception {
    HttpServletRequest processedRequest = request;
    HandlerExecutionChain mappedHandler = null;
    boolean multipartRequestParsed = false;
    WebAsyncManager asyncManager = WebAsyncUtils.getAsyncManager(request);

    try {
        try {
            ModelAndView mv = null;
            Object dispatchException = null;

            try {
                processedRequest = this.checkMultipart(request);
                multipartRequestParsed = processedRequest != request;
                // 根据url对应的地址查找对应控制器类和方法、没有找到则返回DefaultServletHttpRequestHandler类
                mappedHandler = this.getHandler(processedRequest);
                if (mappedHandler == null) {
                    this.noHandlerFound(processedRequest, response);
                    return;
                }
		// 控制器适配器
                HandlerAdapter ha = this.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 ((new ServletWebRequest(request, response)).checkNotModified(lastModified) && isGet) {
                        return;
                    }
                }
		// 检查是否有拦截器、有的话执行拦截器对应的方法.
                if (!mappedHandler.applyPreHandle(processedRequest, response)) {
                    return;
                }
		// 根据url查询到对应的控制器类中的方法、现在由控制器适配器调用该控制器类方法、然后返回控制类方法返回的视图
                mv = ha.handle(processedRequest, response, mappedHandler.getHandler());
                if (asyncManager.isConcurrentHandlingStarted()) {
                    return;
                }

                this.applyDefaultViewName(processedRequest, mv);
                // 拦截器方法、执行Controller返回后执行
                mappedHandler.applyPostHandle(processedRequest, response, mv);
            } catch (Exception var20) {
                dispatchException = var20;
            } catch (Throwable var21) {
                dispatchException = new NestedServletException("Handler dispatch failed", var21);
            }

            this.processDispatchResult(processedRequest, response, mappedHandler, mv, (Exception)dispatchException);
        } catch (Exception var22) {
            this.triggerAfterCompletion(processedRequest, response, mappedHandler, var22);
        } catch (Throwable var23) {
            this.triggerAfterCompletion(processedRequest, response, mappedHandler, new NestedServletException("Handler processing failed", var23));
        }

    } finally {
        if (asyncManager.isConcurrentHandlingStarted()) {
            if (mappedHandler != null) {
                mappedHandler.applyAfterConcurrentHandlingStarted(processedRequest, response);
            }
        } else if (multipartRequestParsed) {
            this.cleanupMultipart(processedRequest);
        }

    }
}