springmvc-4.3.7.RELEASE核心源码断点分析

springmvc请求执行流程

springmvc核心源码

核心方法：DispatcherServlet.doDispatcher

该方法控制着springmvc处理和响应请求的核心流程，源码和注释如下：

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 获取 HandlerExecutionChain 对象            mappedHandler = getHandler(processedRequest);            if (mappedHandler == null || mappedHandler.getHandler() == null) {                noHandlerFound(processedRequest, response);                return;            }            // 通过 HandlerExecutionChain 获取 HandlerAdaptor 对象            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;                }            }            // 通过 HandlerExecutionChain 调用拦截器的 preHandle 方法             if (!mappedHandler.applyPreHandle(processedRequest, response)) {                return;            }            // 通过 HandlerAdaptor 对象调用目标handler的目标方法得到ModelAndView            mv = ha.handle(processedRequest, response, mappedHandler.getHandler());            if (asyncManager.isConcurrentHandlingStarted()) {                return;            }            applyDefaultViewName(processedRequest, mv);            //通过 HandlerExecutionChain 调用拦截器的postHandle方法            mappedHandler.applyPostHandle(processedRequest, response, mv);        }        catch (Exception ex) { //上述调用的过程中如果发生异常            dispatchException = ex;        }        catch (Throwable err) { //上述调用的过程中如果发生异常            dispatchException = new NestedServletException("Handler dispatch failed", err);        }        // 由ViewResolver组件根据ModelAndView对象得到实际的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);            }        }    }}

相关方法

DispatcherServlet.getHandler（dispatcherServlet.handlerMappings 获取 HandlerExecutionChain 对象）

/** * 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（通过 HandlerExecutionChain 调用拦截器的 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：(通过 HandlerExecutionChain 调用拦截器的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（通过 HandlerExecutionChain 调用拦截器的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（渲染视图，最终执行转发操作）

• 上述调用的过程中是否发生异常，由HandlerExceptionResolver组件处理异常，得到新的ModelAndView对象
  
• 通过 HandlerExecutionChain 调用拦截器的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);            // 上述调用的过程中是否发生异常，由HandlerExceptionResolver组件处理异常，得到新的ModelAndView对象            mv = processHandlerException(request, response, handler, exception);            errorView = (mv != null);        }    }    // Did the handler return a view to render?    // 由ViewResolver组件根据ModelAndView对象得到实际的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) {        // 通过 HandlerExecutionChain 调用拦截器的afterCompletion方法        mappedHandler.triggerAfterCompletion(request, response, null);    }}

DispatcherServlet.processHandlerException（由异常解析器处理异常，返回新的异常模型视图对象）

/** * 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...    // 上述调用的过程中是否发生异常，由HandlerExceptionResolver组件处理异常，得到新的ModelAndView对象    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（渲染视图具体执行方法）

• 由ViewResolver组件根据ModelAndView对象得到实际的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组件根据ModelAndView对象得到实际的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());        }        // 渲染视图        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组件根据ModelAndView对象得到实际的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 */@Overridepublic 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);    //////////渲染视图的最后步骤    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. */@Overrideprotected 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() + "'");        }        // 最终的请求转发代码        rd.forward(request, response);    }}