springMVC 拦截器源码解析

前言：这两天学习了代理模式，自然想到了 springmvc 的 aop 使用的就是动态代理，拦截器使用的就是 jdk 的动态代理。今天看了看源码，记录一下。转载请注明出处：https://www.cnblogs.com/yuxiaole/p/9969360.html

springMVC 的拦截器使用移步：Java Servlet 过滤器与 springmvc 拦截器的区别？

源码解析

　　springMVC 的所有连接入口都会进入 DispatcherServlet，然后在这里面去调用真正的 Controller。而拦截器要达到的作用则是在调用 Controller 前后去做一些事情。所以现在需要看看 DispatcherServlet 的源码。

DispatcherServlet

　　DispatcherServlet 的源码入口在 doService() 方法。

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() 方法里面处理了一些信息之后，调用了 doDispatch() 方法。

    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() 方法中通过 this.getHandler(processedRequest); 获取到了处理器链 HandlerExecutionChain mappedHandle 之后，去执行了  mappedHandler.applyPreHandle(processedRequest, response) 方法，从而执行了拦截器的 preHandle 方法，如果返回为 false，则会调用处理器链的 triggerAfterCompletion 方法，然后 DispatchServlet 类中会直接 retreturn；如果返回为 true，则继续。

　　然后调用了 HandlerAdapter 的 handler() 方法；

　　然后调用了 mappedHandler.applyPostHandle(processedRequest, response, mv); 方法，从而执行了拦截器的 postHandle 方法；

　　然后调用了 this.processDispatchResult(processedRequest, response, mappedHandler, mv, (Exception)dispatchException); 方法；在 processDispatchResult() 方法里面渲染了对应的视图，然后调用了 mappedHandler.triggerAfterCompletion(request, response, (Exception)null); 方法，从而执行了拦截器的 afterCompletion 方法。

　　processDispatchResult() 源码如下：

    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);
            }

        }
    }

　　从 doDispatch() 方法这里主要需要知道 HandlerExecutionChain mappedHandler = this.getHandler(processedRequest); 这一句调用的 getHandler() 方法，源码如下。

　　getHandle() 方法里是通过 HandlerMapping 的 getHandler 方法返回 HandlerExecutionChain 的。

　　从代码中不难看出整个逻辑就是依次判断 servlet 中的每个 handlerMapping 是否能够匹配该请求，直到找到那个匹配的然后返回处理结果。

    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 类

　　applyPreHandle() 方法源码如下：可以看出是顺序调用拦截器的 preHandle() 方法。preHandle 返回 false 时调用了 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() 方法源码如下：可以看出这里是逆序调用 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() 方法源码如下：可以看出这里也是逆序调用 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);
                }
            }
        }

    }

　　

转载请注明出处：https://www.cnblogs.com/yuxiaole/p/9969360.html