SpringMVC運行原理

 

 

 

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按照上邊的執行流程圖，我們可以看出一個SpringMVC整體的一個執行輪廓，下面我們具體來分析下

 

首先服務器接收到一個請求，匹配並調用了我們的前端控制器（DispatcherServlet）也叫中央處理器的請求路徑，在web.xml文件中配置，我們來看下配置文件

<servlet>
        <servlet-name>springmvc</servlet-name>
        <servlet-class>org.springframework.web.servlet.DispatcherServlet</servlet-class>
        <init-param>
            <param-name>contextConfigLocation</param-name>
            <param-value>classpath:springmvc.xml</param-value>
        </init-param>
        <load-on-startup>1</load-on-startup>
</servlet>
<servlet-mapping>
    <servlet-name>springmvc</servlet-name>
　　<!-- / 代表匹配所有除了jsp文件的請求 -->
    <url-pattern>/</url-pattern>
</servlet-mapping>

因為DispatcherServlet實際上是間接的繼承了我們的HttpServlet，所以它就相當於一個Servlet，SpringMVC幫我們封裝好的一個Servlet，下面是繼承體系

 

 

 所以說，當來了一個請求后，WEB容器將把請求交給我們的DispatcherServlet進行處理

DispatcherServlet接收到請求后，會把我們的請求信息交給HandlerMapping處理器映射器進行處理

HandlerMapping根據請求的URL信息去查找匹配的URL的Handler，如果查找成，並返回一個執行鏈，下面來看下底層執行代碼

 protected HandlerExecutionChain getHandler(HttpServletRequest request) throws Exception {
        Iterator var2 = this.handlerMappings.iterator();

        HandlerExecutionChain handler;
        do {
            if (!var2.hasNext()) {
                return null;
            }

            HandlerMapping hm = (HandlerMapping)var2.next();
            if (this.logger.isTraceEnabled()) {
                this.logger.trace("Testing handler map [" + hm + "] in DispatcherServlet with name '" + this.getServletName() + "'");
            }

            handler = hm.getHandler(request);//根據request對象獲取handler，獲取到的話將返回一個對象，沒有的話將返回null  有興趣童鞋自行深入查看
        } while(handler == null);//如果handler為null繼續執行循環

        return handler;
    }

如果沒有找到的話將執行以下代碼

 protected void noHandlerFound(HttpServletRequest request, HttpServletResponse response) throws Exception {
        if (pageNotFoundLogger.isWarnEnabled()) {
            pageNotFoundLogger.warn("No mapping found for HTTP request with URI [" + getRequestUri(request) + "] in DispatcherServlet with name '" + this.getServletName() + "'");
        }

        if (this.throwExceptionIfNoHandlerFound) {
            ServletServerHttpRequest sshr = new ServletServerHttpRequest(request);
            throw new NoHandlerFoundException(sshr.getMethod().name(), sshr.getServletRequest().getRequestURI(), sshr.getHeaders());
        } else {
            response.sendError(404);//響應404
        }
    }

找到成功的情況下，DispatcherServlet再次請求 處理器適配器（HandlerAdapter）調用相應的Handler 進行處理返回 ModelAndView 給 DispatcherServlet，底層代碼，粗略看下即可，不是重點

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

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

            try {
                processedRequest = this.checkMultipart(request);
                multipartRequestParsed = processedRequest != request;
                mappedHandler = this.getHandler(processedRequest);
                if (mappedHandler == null || mappedHandler.getHandler() == null) {
                    this.noHandlerFound(processedRequest, response);
                    return;
                }

                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 (this.logger.isDebugEnabled()) {
                        this.logger.debug("Last-Modified value for [" + getRequestUri(request) + "] is: " + lastModified);
                    }

                    if ((new ServletWebRequest(request, response)).checkNotModified(lastModified) && isGet) {
                        return;
                    }
                }

                if (!mappedHandler.applyPreHandle(processedRequest, response)) {
                    return;
                }

                mv = ha.handle(processedRequest, response, mappedHandler.getHandler()); //在這里邊調用相應的Handler，並通過這個方法返回ModelAndModel給DispatcherServlet
                if (asyncManager.isConcurrentHandlingStarted()) {
                    return;
                }

                this.applyDefaultViewName(request, mv);
                mappedHandler.applyPostHandle(processedRequest, response, mv);
            } catch (Exception var19) {
                dispatchException = var19;
            }

            this.processDispatchResult(processedRequest, response, mappedHandler, mv, dispatchException);
        } catch (Exception var20) {
            this.triggerAfterCompletion(processedRequest, response, mappedHandler, var20);
        } catch (Error var21) {
            this.triggerAfterCompletionWithError(processedRequest, response, mappedHandler, var21);
        } finally {
            if (asyncManager.isConcurrentHandlingStarted()) {
                if (mappedHandler != null) {
                    mappedHandler.applyAfterConcurrentHandlingStarted(processedRequest, response);
                }
            } else if (multipartRequestParsed) {
                this.cleanupMultipart(processedRequest);
            }

        }

    }

然后DispatcherServlet將ModelAndView請求對應的ViewResolver（視圖解析器）解析視圖，然后返回具體的View，底層實現

 protected View resolveViewName(String viewName, Map<String, Object> model, Locale locale, HttpServletRequest request) throws Exception {
        Iterator var5 = this.viewResolvers.iterator();

        View view;
        do {
            if (!var5.hasNext()) {
                return null;
            }

            ViewResolver viewResolver = (ViewResolver)var5.next();
            view = viewResolver.resolveViewName(viewName, locale);
        } while(view == null);

        return view;
    }

DispatcherServlet對View視圖進行渲染，也就是把模型數據填充到視圖里邊，底層執行代碼

protected void render(ModelAndView mv, HttpServletRequest request, HttpServletResponse response) throws Exception {
        Locale locale = this.localeResolver.resolveLocale(request);
        response.setLocale(locale);
        View view;
        if (mv.isReference()) {
            view = this.resolveViewName(mv.getViewName(), mv.getModelInternal(), locale, request);
            if (view == null) {
                throw new ServletException("Could not resolve view with name '" + mv.getViewName() + "' in servlet with name '" + this.getServletName() + "'");
            }
        } else {
            view = mv.getView();
            if (view == null) {
                throw new ServletException("ModelAndView [" + mv + "] neither contains a view name nor a " + "View object in servlet with name '" + this.getServletName() + "'");
            }
        }

        if (this.logger.isDebugEnabled()) {
            this.logger.debug("Rendering view [" + view + "] in DispatcherServlet with name '" + this.getServletName() + "'");
        }

        try {
            view.render(mv.getModelInternal(), request, response);
        } catch (Exception var7) {
            if (this.logger.isDebugEnabled()) {
                this.logger.debug("Error rendering view [" + view + "] in DispatcherServlet with name '" + this.getServletName() + "'", var7);
            }

            throw var7;
        }
    }

最后DispatcherServlet將視圖傳遞給前台

 

PS：

Spring MVC核心組件：
    1.DispatcherServlet(中央處理器)：將請求轉發給控制器

    2.Controller（控制器）：處理請求的控制器

    3.HandlerMapping（映射處理器）：負責映射中央處理器轉發給Controller時的映射策略

    4.ModelAndView：服務器返回數據以及視圖層的封裝類

    5.ViewResolver（視圖解析器）：解析具體的視圖

 

當用戶發起請求后,執行DiapacherServlet,如果是JSP直接調用jsp頁面.如果不是JSP,DiapacherServlet調用HandlerMapping判斷請求URL是否合法,如果URL不存在報錯,如果URL存在使用HandlerAdapter調用具體的HandlerMethod,當Handler執行完成后會返回ModelAndView,會被ViewResovler解析,調用具體的物理視圖.
最終響應給客戶端瀏覽器.