springmvc-4.3.7.RELEASE核心源碼斷點分析

springmvc請求執行流程

springmvc核心源碼

核心方法：DispatcherServlet.doDispatcher

該方法控制着springmvc處理和響應請求的核心流程，源碼和註釋如下：

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 = checkMultipart(request);
            multipartRequestParsed = (processedRequest != request);


            // 由 dispatcherServlet.handlerMappings 獲取 HandlerExecutionChain 對象
            mappedHandler = getHandler(processedRequest);
            if (mappedHandler == null || mappedHandler.getHandler() == null) {
                noHandlerFound(processedRequest, response);
                return;
            }

            // 通過 HandlerExecutionChain 獲取 HandlerAdaptor 對象
            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 (logger.isDebugEnabled()) {
                    logger.debug("Last-Modified value for [" + getRequestUri(request) + "] is: " + lastModified);
                }
                if (new ServletWebRequest(request, response).checkNotModified(lastModified) && isGet) {
                    return;
                }
            }


            // 通過 HandlerExecutionChain 調用攔截器的 preHandle 方法 
            if (!mappedHandler.applyPreHandle(processedRequest, response)) {
                return;
            }

            // 通過 HandlerAdaptor 對象調用目標handler的目標方法得到ModelAndView
            mv = ha.handle(processedRequest, response, mappedHandler.getHandler());

            if (asyncManager.isConcurrentHandlingStarted()) {
                return;
            }

            applyDefaultViewName(processedRequest, mv);

            //通過 HandlerExecutionChain 調用攔截器的postHandle方法
            mappedHandler.applyPostHandle(processedRequest, response, mv);
        }
        catch (Exception ex) { //上述調用的過程中如果發生異常
            dispatchException = ex;
        }
        catch (Throwable err) { //上述調用的過程中如果發生異常
            dispatchException = new NestedServletException("Handler dispatch failed", err);
        }

        // 由ViewResolver組件根據ModelAndView對象得到實際的View
        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.
            if (multipartRequestParsed) {
                cleanupMultipart(processedRequest);
            }
        }
    }
}

相關方法

DispatcherServlet.getHandler（dispatcherServlet.handlerMappings 獲取 HandlerExecutionChain 對象）

/**
 * Return the HandlerExecutionChain for this request.
 * <p>Tries all handler mappings in order.
 * @param request current HTTP request
 * @return the HandlerExecutionChain, or {@code null} if no handler could be found
 */
protected HandlerExecutionChain getHandler(HttpServletRequest request) throws Exception {
    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;
}

HandlerExecutionChain.applyPreHandle（通過 HandlerExecutionChain 調用攔截器的 preHandle 方法 ）

/**
 * Apply preHandle methods of registered interceptors.
 * @return {@code true} if the execution chain should proceed with the
 * next interceptor or the handler itself. Else, DispatcherServlet assumes
 * that this interceptor has already dealt with the response itself.
 */
boolean applyPreHandle(HttpServletRequest request, HttpServletResponse response) throws Exception {
    HandlerInterceptor[] interceptors = getInterceptors();
    if (!ObjectUtils.isEmpty(interceptors)) {
        for (int i = 0; i < interceptors.length; i++) {
            HandlerInterceptor interceptor = interceptors[i];
            if (!interceptor.preHandle(request, response, this.handler)) {
                triggerAfterCompletion(request, response, null);
                return false;
            }
            this.interceptorIndex = i;
        }
    }
    return true;
}

HandlerExecutionChain.applyPostHandle：(通過 HandlerExecutionChain 調用攔截器的postHandle方法)

/**
 * Apply postHandle methods of registered interceptors.
 */
void applyPostHandle(HttpServletRequest request, HttpServletResponse response, ModelAndView mv) throws Exception {
    HandlerInterceptor[] interceptors = getInterceptors();
    if (!ObjectUtils.isEmpty(interceptors)) {
        for (int i = interceptors.length - 1; i >= 0; i--) {
            HandlerInterceptor interceptor = interceptors[i];
            interceptor.postHandle(request, response, this.handler, mv);
        }
    }
}

HandlerExecutionChain.triggerAfterCompletion（通過 HandlerExecutionChain 調用攔截器的afterCompletion方法）

/**
 * Trigger afterCompletion callbacks on the mapped HandlerInterceptors.
 * Will just invoke afterCompletion for all interceptors whose preHandle invocation
 * has successfully completed and returned true.
 */
void triggerAfterCompletion(HttpServletRequest request, HttpServletResponse response, Exception ex)
        throws Exception {

    HandlerInterceptor[] interceptors = getInterceptors();
    if (!ObjectUtils.isEmpty(interceptors)) {
        for (int i = this.interceptorIndex; i >= 0; i--) {
            HandlerInterceptor interceptor = interceptors[i];
            try {
                interceptor.afterCompletion(request, response, this.handler, ex);
            }
            catch (Throwable ex2) {
                logger.error("HandlerInterceptor.afterCompletion threw exception", ex2);
            }
        }
    }
}

HandlerExecutionChain.applyAfterConcurrentHandlingStarted（）

/**
 * Apply afterConcurrentHandlerStarted callback on mapped AsyncHandlerInterceptors.
 */
void applyAfterConcurrentHandlingStarted(HttpServletRequest request, HttpServletResponse response) {
    HandlerInterceptor[] interceptors = getInterceptors();
    if (!ObjectUtils.isEmpty(interceptors)) {
        for (int i = interceptors.length - 1; i >= 0; i--) {
            if (interceptors[i] instanceof AsyncHandlerInterceptor) {
                try {
                    AsyncHandlerInterceptor asyncInterceptor = (AsyncHandlerInterceptor) interceptors[i];
                    asyncInterceptor.afterConcurrentHandlingStarted(request, response, this.handler);
                }
                catch (Throwable ex) {
                    logger.error("Interceptor [" + interceptors[i] + "] failed in afterConcurrentHandlingStarted", ex);
                }
            }
        }
    }
}

DispatcherServlet.processDispatchResult（渲染視圖，最終執行轉發操作）

• 上述調用的過程中是否發生異常，由HandlerExceptionResolver組件處理異常，得到新的ModelAndView對象
  
• 通過 HandlerExecutionChain 調用攔截器的afterCompletion方法
  

/**
 * Handle the result of handler selection and handler invocation, which is
 * either a ModelAndView or an Exception to be resolved to a ModelAndView.
 */
private void processDispatchResult(HttpServletRequest request, HttpServletResponse response,
        HandlerExecutionChain mappedHandler, ModelAndView mv, Exception exception) throws Exception {

    boolean errorView = false;

    if (exception != null) {
        if (exception instanceof ModelAndViewDefiningException) {
            logger.debug("ModelAndViewDefiningException encountered", exception);
            mv = ((ModelAndViewDefiningException) exception).getModelAndView();
        }
        else {
            Object handler = (mappedHandler != null ? mappedHandler.getHandler() : null);

            // 上述調用的過程中是否發生異常，由HandlerExceptionResolver組件處理異常，得到新的ModelAndView對象
            mv = processHandlerException(request, response, handler, exception);
            errorView = (mv != null);
        }
    }

    // Did the handler return a view to render?
    // 由ViewResolver組件根據ModelAndView對象得到實際的View
    if (mv != null && !mv.wasCleared()) {
        render(mv, request, response);
        if (errorView) {
            WebUtils.clearErrorRequestAttributes(request);
        }
    }
    else {
        if (logger.isDebugEnabled()) {
            logger.debug("Null ModelAndView returned to DispatcherServlet with name '" + getServletName() +
                    "': assuming HandlerAdapter completed request handling");
        }
    }

    if (WebAsyncUtils.getAsyncManager(request).isConcurrentHandlingStarted()) {
        // Concurrent handling started during a forward
        return;
    }

    if (mappedHandler != null) {
        // 通過 HandlerExecutionChain 調用攔截器的afterCompletion方法
        mappedHandler.triggerAfterCompletion(request, response, null);
    }
}

DispatcherServlet.processHandlerException（由異常解析器處理異常，返回新的異常模型視圖對象）

/**
 * Determine an error ModelAndView via the registered HandlerExceptionResolvers.
 * @param request current HTTP request
 * @param response current HTTP response
 * @param handler the executed handler, or {@code null} if none chosen at the time of the exception
 * (for example, if multipart resolution failed)
 * @param ex the exception that got thrown during handler execution
 * @return a corresponding ModelAndView to forward to
 * @throws Exception if no error ModelAndView found
 */
protected ModelAndView processHandlerException(HttpServletRequest request, HttpServletResponse response,
        Object handler, Exception ex) throws Exception {

    // Check registered HandlerExceptionResolvers...
    // 上述調用的過程中是否發生異常，由HandlerExceptionResolver組件處理異常，得到新的ModelAndView對象
    ModelAndView exMv = null;
    for (HandlerExceptionResolver handlerExceptionResolver : this.handlerExceptionResolvers) {
        exMv = handlerExceptionResolver.resolveException(request, response, handler, ex);
        if (exMv != null) {
            break;
        }
    }
    if (exMv != null) {
        if (exMv.isEmpty()) {
            request.setAttribute(EXCEPTION_ATTRIBUTE, ex);
            return null;
        }
        // We might still need view name translation for a plain error model...
        if (!exMv.hasView()) {
            exMv.setViewName(getDefaultViewName(request));
        }
        if (logger.isDebugEnabled()) {
            logger.debug("Handler execution resulted in exception - forwarding to resolved error view: " + exMv, ex);
        }
        WebUtils.exposeErrorRequestAttributes(request, ex, getServletName());
        return exMv;
    }

    throw ex;
}

DispatcherServlet.render（渲染視圖具體執行方法）

• 由ViewResolver組件根據ModelAndView對象得到實際的View
  

/**
 * Render the given ModelAndView.
 * <p>This is the last stage in handling a request. It may involve resolving the view by name.
 * @param mv the ModelAndView to render
 * @param request current HTTP servlet request
 * @param response current HTTP servlet response
 * @throws ServletException if view is missing or cannot be resolved
 * @throws Exception if there's a problem rendering the view
 */
protected void render(ModelAndView mv, HttpServletRequest request, HttpServletResponse response) throws Exception {
    // Determine locale for request and apply it to the response.
    Locale locale = this.localeResolver.resolveLocale(request);
    response.setLocale(locale);

    View view;
    if (mv.isReference()) {

        // We need to resolve the view name.
        // 由ViewResolver組件根據ModelAndView對象得到實際的View
        view = 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 '" + getServletName() + "'");
        }

    }
    else {
        // No need to lookup: the ModelAndView object contains the actual View object.
        view = mv.getView();
        if (view == null) {
            throw new ServletException("ModelAndView [" + mv + "] neither contains a view name nor a " +
                    "View object in servlet with name '" + getServletName() + "'");
        }
    }

    // Delegate to the View object for rendering.
    if (logger.isDebugEnabled()) {
        logger.debug("Rendering view [" + view + "] in DispatcherServlet with name '" + getServletName() + "'");
    }
    try {
        if (mv.getStatus() != null) {
            response.setStatus(mv.getStatus().value());
        }
        // 渲染視圖
        view.render(mv.getModelInternal(), request, response);
    }
    catch (Exception ex) {
        if (logger.isDebugEnabled()) {
            logger.debug("Error rendering view [" + view + "] in DispatcherServlet with name '" +
                    getServletName() + "'", ex);
        }
        throw ex;
    }
}

DispatcherServlet.resolveViewName(由ViewResolver組件根據ModelAndView對象得到實際的View)

/**
 * Resolve the given view name into a View object (to be rendered).
 * <p>The default implementations asks all ViewResolvers of this dispatcher.
 * Can be overridden for custom resolution strategies, potentially based on
 * specific model attributes or request parameters.
 * @param viewName the name of the view to resolve
 * @param model the model to be passed to the view
 * @param locale the current locale
 * @param request current HTTP servlet request
 * @return the View object, or {@code null} if none found
 * @throws Exception if the view cannot be resolved
 * (typically in case of problems creating an actual View object)
 * @see ViewResolver#resolveViewName
 */
protected View resolveViewName(String viewName, Map<String, Object> model, Locale locale,
        HttpServletRequest request) throws Exception {

    for (ViewResolver viewResolver : this.viewResolvers) {
        View view = viewResolver.resolveViewName(viewName, locale);
        if (view != null) {
            return view;
        }
    }
    return null;
}

org.springframework.web.servlet.view.AbstractView.render

/**
 * Prepares the view given the specified model, merging it with static
 * attributes and a RequestContext attribute, if necessary.
 * Delegates to renderMergedOutputModel for the actual rendering.
 * @see #renderMergedOutputModel
 */
@Override
public void render(Map<String, ?> model, HttpServletRequest request, HttpServletResponse response) throws Exception {
    if (logger.isTraceEnabled()) {
        logger.trace("Rendering view with name '" + this.beanName + "' with model " + model +
            " and static attributes " + this.staticAttributes);
    }

    Map<String, Object> mergedModel = createMergedOutputModel(model, request, response);
    prepareResponse(request, response);
    //////////渲染視圖的最後步驟
    renderMergedOutputModel(mergedModel, getRequestToExpose(request), response);
}

org.springframework.web.servlet.view.InternalResourceView.renderMergedOutputModel

/**
 * Render the internal resource given the specified model.
 * This includes setting the model as request attributes.
 */
@Override
protected void renderMergedOutputModel(
        Map<String, Object> model, HttpServletRequest request, HttpServletResponse response) throws Exception {

    // Expose the model object as request attributes.
    exposeModelAsRequestAttributes(model, request);

    // Expose helpers as request attributes, if any.
    exposeHelpers(request);

    // Determine the path for the request dispatcher.
    String dispatcherPath = prepareForRendering(request, response);

    // Obtain a RequestDispatcher for the target resource (typically a JSP).
    RequestDispatcher rd = getRequestDispatcher(request, dispatcherPath);
    if (rd == null) {
        throw new ServletException("Could not get RequestDispatcher for [" + getUrl() +
                "]: Check that the corresponding file exists within your web application archive!");
    }

    // If already included or response already committed, perform include, else forward.
    if (useInclude(request, response)) {
        response.setContentType(getContentType());
        if (logger.isDebugEnabled()) {
            logger.debug("Including resource [" + getUrl() + "] in InternalResourceView '" + getBeanName() + "'");
        }
        rd.include(request, response);
    }

    else {
        // Note: The forwarded resource is supposed to determine the content type itself.
        if (logger.isDebugEnabled()) {
            logger.debug("Forwarding to resource [" + getUrl() + "] in InternalResourceView '" + getBeanName() + "'");
        }

        // 最終的請求轉發代碼
        rd.forward(request, response);
    }
}