springMVC 攔截器源碼解析

時間  2019-11-11
標籤 springmvc 攔截 源碼 解析 欄目 Spring 简体版
原文   原文鏈接

前言：這兩天學習了代理模式，天然想到了 springmvc 的 aop 使用的就是動態代理，攔截器使用的就是 jdk 的動態代理。今天看了看源碼，記錄一下。轉載請註明出處：https://www.cnblogs.com/yuxiaole/p/9969360.htmlhtml

springMVC 的攔截器使用移步：Java Servlet 過濾器與 springmvc 攔截器的區別？web

源碼解析

　　springMVC 的全部鏈接入口都會進入 DispatcherServlet，而後在這裏面去調用真正的 Controller。而攔截器要達到的做用則是在調用 Controller 先後去作一些事情。因此如今須要看看 DispatcherServlet 的源碼。spring

DispatcherServlet 

　　DispatcherServlet 的源碼入口在 doService() 方法。mvc

protected void doService(HttpServletRequest request, HttpServletResponse response) throws Exception {
        if(this.logger.isDebugEnabled()) {
            String resumed = WebAsyncUtils.getAsyncManager(request).hasConcurrentResult()?" resumed":"";
            this.logger.debug("DispatcherServlet with name '" + this.getServletName() + "'" + resumed + " processing " + request.getMethod() + " request for [" + getRequestUri(request) + "]");
        }

        Map<String, Object> attributesSnapshot = null;
        if(WebUtils.isIncludeRequest(request)) {
            attributesSnapshot = new HashMap();
            Enumeration attrNames = request.getAttributeNames();

            label108:
            while(true) {
                String attrName;
                do {
                    if(!attrNames.hasMoreElements()) {
                        break label108;
                    }

                    attrName = (String)attrNames.nextElement();
                } while(!this.cleanupAfterInclude && !attrName.startsWith("org.springframework.web.servlet"));

                attributesSnapshot.put(attrName, request.getAttribute(attrName));
            }
        }

        request.setAttribute(WEB_APPLICATION_CONTEXT_ATTRIBUTE, this.getWebApplicationContext());
        request.setAttribute(LOCALE_RESOLVER_ATTRIBUTE, this.localeResolver);
        request.setAttribute(THEME_RESOLVER_ATTRIBUTE, this.themeResolver);
        request.setAttribute(THEME_SOURCE_ATTRIBUTE, this.getThemeSource());
        FlashMap inputFlashMap = this.flashMapManager.retrieveAndUpdate(request, response);
        if(inputFlashMap != null) {
            request.setAttribute(INPUT_FLASH_MAP_ATTRIBUTE, Collections.unmodifiableMap(inputFlashMap));
        }

        request.setAttribute(OUTPUT_FLASH_MAP_ATTRIBUTE, new FlashMap());
        request.setAttribute(FLASH_MAP_MANAGER_ATTRIBUTE, this.flashMapManager);

        try {
            this.doDispatch(request, response);
        } finally {
            if(!WebAsyncUtils.getAsyncManager(request).isConcurrentHandlingStarted() && attributesSnapshot != null) {
                this.restoreAttributesAfterInclude(request, attributesSnapshot);
            }

        }

    }

　　doService() 方法裏面處理了一些信息以後，調用了 doDispatch() 方法。app

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

                    this.applyDefaultViewName(processedRequest, mv);
                    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);
            }

        }
    }

　　doDispatch() 方法中經過 this.getHandler(processedRequest); 獲取到了處理器鏈 HandlerExecutionChain mappedHandle 以後，去執行了  mappedHandler.applyPreHandle(processedRequest, response) 方法，從而執行了攔截器的 preHandle 方法，若是返回爲 false，則會調用處理器鏈的 triggerAfterCompletion 方法，而後 DispatchServlet 類中會直接 retreturn；若是返回爲 true，則繼續。async

　　而後調用了 HandlerAdapter 的 handler() 方法；post

　　而後調用了 mappedHandler.applyPostHandle(processedRequest, response, mv); 方法，從而執行了攔截器的 postHandle 方法；學習

　　而後調用了 this.processDispatchResult(processedRequest, response, mappedHandler, mv, (Exception)dispatchException); 方法；在 processDispatchResult() 方法裏面渲染了對應的視圖，而後調用了 mappedHandler.triggerAfterCompletion(request, response, (Exception)null); 方法，從而執行了攔截器的 afterCompletion 方法。this

　　processDispatchResult() 源碼以下：url

    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) {
                this.logger.debug("ModelAndViewDefiningException encountered", exception);
                mv = ((ModelAndViewDefiningException)exception).getModelAndView();
            } else {
                Object handler = mappedHandler != null?mappedHandler.getHandler():null;
                mv = this.processHandlerException(request, response, handler, exception);
                errorView = mv != null;
            }
        }

        if(mv != null && !mv.wasCleared()) {
            this.render(mv, request, response);
            if(errorView) {
                WebUtils.clearErrorRequestAttributes(request);
            }
        } else if(this.logger.isDebugEnabled()) {
            this.logger.debug("Null ModelAndView returned to DispatcherServlet with name '" + this.getServletName() + "': assuming HandlerAdapter completed request handling");
        }

        if(!WebAsyncUtils.getAsyncManager(request).isConcurrentHandlingStarted()) {
            if(mappedHandler != null) {
                mappedHandler.triggerAfterCompletion(request, response, (Exception)null);
            }

        }
    }

　　從 doDispatch() 方法這裏主要須要知道 HandlerExecutionChain mappedHandler = this.getHandler(processedRequest); 這一句調用的 getHandler() 方法，源碼以下。

　　getHandle() 方法裏是經過 HandlerMapping 的 getHandler 方法返回 HandlerExecutionChain 的。

　　從代碼中不難看出整個邏輯就是依次判斷 servlet 中的每一個 handlerMapping 是否可以匹配該請求，直到找到那個匹配的而後返回處理結果。

    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);
        } while(handler == null);

        return handler;
    }

HandlerExecutionChain 類

　　applyPreHandle() 方法源碼以下：能夠看出是順序調用攔截器的 preHandle() 方法。preHandle 返回 false 時調用了 triggerAfterCompletion 方法。

    boolean applyPreHandle(HttpServletRequest request, HttpServletResponse response) throws Exception {
        HandlerInterceptor[] interceptors = this.getInterceptors();
        if(!ObjectUtils.isEmpty(interceptors)) {
            for(int i = 0; i < interceptors.length; this.interceptorIndex = i++) {
                HandlerInterceptor interceptor = interceptors[i];
                if(!interceptor.preHandle(request, response, this.handler)) {
                    this.triggerAfterCompletion(request, response, (Exception)null);
                    return false;
                }
            }
        }

        return true;
    }

　　applyPostHandle() 方法源碼以下：能夠看出這裏是逆序調用 postHandle 方法。

    void applyPostHandle(HttpServletRequest request, HttpServletResponse response, ModelAndView mv) throws Exception {
        HandlerInterceptor[] interceptors = this.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);
            }
        }

    }

　triggerAfterCompletion() 方法源碼以下：能夠看出這裏也是逆序調用 afterCompletion 方法。

    void triggerAfterCompletion(HttpServletRequest request, HttpServletResponse response, Exception ex) throws Exception {
        HandlerInterceptor[] interceptors = this.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 var8) {
                    logger.error("HandlerInterceptor.afterCompletion threw exception", var8);
                }
            }
        }

    }

 　　

轉載請註明出處：https://www.cnblogs.com/yuxiaole/p/9969360.html

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