DispatcherServlet 源码分析

    /**
     * Overridden method of {@link HttpServletBean}, invoked after any bean 
     properties
     * have been set. Creates this servlet's WebApplicationContext.
     */
    @Override
    protected final void initServletBean() throws ServletException {
        getServletContext().log("Initializing Spring " + getClass().getSimpleName()
                + " '" + getServletName() + "'");
        if (logger.isInfoEnabled()) {
            logger.info("Initializing Servlet '" + getServletName() + "'");
        }
        long startTime = System.currentTimeMillis();
        try {
            //创建ApplicationContext容器
            this.webApplicationContext = initWebApplicationContext();
            initFrameworkServlet();
        }
        catch (ServletException | RuntimeException ex) {
            logger.error("Context initialization failed", ex);
            throw ex;
        }
        if (logger.isDebugEnabled()) {
            String value = this.enableLoggingRequestDetails ?
                    "shown which may lead to unsafe logging of potentially sensitive 
            data" :
            "masked to prevent unsafe logging of potentially sensitive data";
            logger.debug("enableLoggingRequestDetails='" +
                    this.enableLoggingRequestDetails +
                    "': request parameters and headers will be " + value);
        }
        if (logger.isInfoEnabled()) {
            logger.info("Completed initialization in " + (System.currentTimeMillis()
                    - startTime) + " ms");
        }
    }

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;
                Exception dispatchException = null;
                try {
                    processedRequest = this.checkMultipart(request);
                    multipartRequestParsed = processedRequest != request;
                    //1. 获取执⾏链
                    //遍历所有的 HandlerMapping 找到与请求对应的Handler
                    mappedHandler = this.getHandler(processedRequest);
                    if (mappedHandler == null) {
                        this.noHandlerFound(processedRequest, response);
                        return;
                    }
                    //2. 获取适配器
                    //遍历所有的 HandlerAdapter，找到可以处理该 Handler 的
                    HandlerAdapter
                    HandlerAdapter ha =
                            this.getHandlerAdapter(mappedHandler.getHandler());
                    String method = request.getMethod();
                    boolean isGet = HttpMethod.GET.matches(method);
                    if (isGet || HttpMethod.HEAD.matches(method)) {
                        long lastModified = ha.getLastModified(request,
                                mappedHandler.getHandler());
                        if ((new ServletWebRequest(request,
                                response)).checkNotModified(lastModified) && isGet) {
                            return;
                        }
                    }
                    //3. 执⾏拦截器preHandle⽅法
                    if (!mappedHandler.applyPreHandle(processedRequest, response))
                    {
                        return;
                    }
 
                    //4. 执⾏⽬标⽅法
                    mv = ha.handle(processedRequest, response,
                            mappedHandler.getHandler());
                    if (asyncManager.isConcurrentHandlingStarted()) {
                        return;
                    }
                    this.applyDefaultViewName(processedRequest, mv);
                    //5. 执⾏拦截器postHandle⽅法
                    mappedHandler.applyPostHandle(processedRequest, response, mv);
                } catch (Exception var20) {
                    dispatchException = var20;
                } catch (Throwable var21) {
                    dispatchException = new NestedServletException("Handler
                            dispatch failed", var21);
                }
                //6. 处理视图, 处理之后执⾏拦截器afterCompletion⽅法
                this.processDispatchResult(processedRequest, response,
                        mappedHandler, mv, (Exception)dispatchException);
            } catch (Exception var22) {
                //7. 执⾏拦截器afterCompletion⽅法
                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);
            }
        }
    }