(转)spring中的拦截器（HandlerInterceptor+MethodInterceptor）

1. 过滤器跟拦截器的区别

在说拦截器之前，不得不说一下过滤器，有时候往往被这两个词搞的头大。

其实我们最先接触的就是过滤器，还记得web.xml中配置的<filter>吗~

你应该知道spring mvc的拦截器是只拦截controller而不拦截jsp,html 页面文件的，如果想要拦截那怎么办？

这就用到过滤器filter了，filter是在servlet前执行的，你也可以理解成过滤器中包含拦截器，一个请求过来，先进行过滤器处理，看程序是否受理该请求。过滤器放过后，程序中的拦截器进行处理。

（1）过滤器（Filter）：当你有一堆东西的时候，你只希望选择符合你要求的某一些东西。定义这些要求的工具，就是过滤器。（理解：就是一堆字母中取一个B）

（2）拦截器（Interceptor）：在一个流程正在进行的时候，你希望干预它的进展，甚至终止它进行，这是拦截器做的事情。（理解：就是一堆字母中，干预他，通过验证的少点，顺便干点别的东西）。

2. spring中的拦截器

在web开发中，拦截器是经常用到的功能。它可以帮我们验证是否登陆、预先设置数据以及统计方法的执行效率等等。

今天就来详细的谈一下spring中的拦截器。spring中拦截器主要分两种，一个是HandlerInterceptor，一个是MethodInterceptor。

2.1 HandlerInterceptor拦截器

HandlerInterceptor是springMVC项目中的拦截器，它拦截的目标是请求的地址，比MethodInterceptor先执行。

实现一个HandlerInterceptor拦截器可以直接实现HandlerInterceptor接口，也可以继承HandlerInterceptorAdapter类。

这两种方法殊途同归，其实HandlerInterceptorAdapter也就是声明了HandlerInterceptor接口中所有方法的默认实现，而我们在继承他之后只需要重写必要的方法。

下面就是HandlerInterceptorAdapter的代码，可以看到一个方法只是默认返回true，另外两个是空方法：

public abstract class HandlerInterceptorAdapter implements HandlerInterceptor {  
  
    /** 
     * This implementation always returns <code>true</code>. 
     */  
    public boolean preHandle(HttpServletRequest request, HttpServletResponse response, Object handler)  
        throws Exception {  
        return true;  
    }  
  
    /** 
     * This implementation is empty. 
     */  
    public void postHandle(  
            HttpServletRequest request, HttpServletResponse response, Object handler, ModelAndView modelAndView)  
            throws Exception {  
    }  
  
    /** 
     * This implementation is empty. 
     */  
    public void afterCompletion(  
            HttpServletRequest request, HttpServletResponse response, Object handler, Exception ex)  
            throws Exception {  
    }  
  
}

这三个方法都是干什么的，有什么作用，什么时候调用，不同的拦截器之间是怎样的调用顺序呢？

先补一张图：

(转)spring中的拦截器（HandlerInterceptor+MethodInterceptor）

这还得参考一下DispatcherServlet的doDispatch方法：

protected void doDispatch(HttpServletRequest request, HttpServletResponse response) throws Exception {  
        HttpServletRequest processedRequest = request;  
        HandlerExecutionChain mappedHandler = null;  
        int interceptorIndex = -1;  
  
        try {  
            ModelAndView mv;  
            boolean errorView = false;  
  
            try {  
                processedRequest = checkMultipart(request);  
  
                // Determine handler for the current request.  
                mappedHandler = getHandler(processedRequest, false);  
                if (mappedHandler == null || mappedHandler.getHandler() == null) {  
                    noHandlerFound(processedRequest, response);  
                    return;  
                }  
  
                // Determine handler adapter for the current request.  
                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()) {  
                        String requestUri = urlPathHelper.getRequestUri(request);  
                        logger.debug("Last-Modified value for [" + requestUri + "] is: " + lastModified);  
                    }  
                    if (new ServletWebRequest(request, response).checkNotModified(lastModified) && isGet) {  
                        return;  
                    }  
                }  
  
                // Apply preHandle methods of registered interceptors.  
                HandlerInterceptor[] interceptors = mappedHandler.getInterceptors();  
                if (interceptors != null) {  
                    for (int i = 0; i < interceptors.length; i++) {  
                        HandlerInterceptor interceptor = interceptors[i];  
                        if (!interceptor.preHandle(processedRequest, response, mappedHandler.getHandler())) {  
                            triggerAfterCompletion(mappedHandler, interceptorIndex, processedRequest, response, null);  
                            return;  
                        }  
                        interceptorIndex = i;  
                    }  
                }  
  
                // Actually invoke the handler.  
                mv = ha.handle(processedRequest, response, mappedHandler.getHandler());  
  
                // Do we need view name translation?  
                if (mv != null && !mv.hasView()) {  
                    mv.setViewName(getDefaultViewName(request));  
                }  
  
                // Apply postHandle methods of registered interceptors.  
                if (interceptors != null) {  
                    for (int i = interceptors.length - 1; i >= 0; i--) {  
                        HandlerInterceptor interceptor = interceptors[i];  
                        interceptor.postHandle(processedRequest, response, mappedHandler.getHandler(), mv);  
                    }  
                }  
            }  
            catch (ModelAndViewDefiningException ex) {  
                logger.debug("ModelAndViewDefiningException encountered", ex);  
                mv = ex.getModelAndView();  
            }  
            catch (Exception ex) {  
                Object handler = (mappedHandler != null ? mappedHandler.getHandler() : null);  
                mv = processHandlerException(processedRequest, response, handler, ex);  
                errorView = (mv != null);  
            }  
  
            // Did the handler return a view to render?  
            if (mv != null && !mv.wasCleared()) {  
                render(mv, processedRequest, 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");  
                }  
            }  
  
            // Trigger after-completion for successful outcome.  
            triggerAfterCompletion(mappedHandler, interceptorIndex, processedRequest, response, null);  
        }  
  
        catch (Exception ex) {  
            // Trigger after-completion for thrown exception.  
            triggerAfterCompletion(mappedHandler, interceptorIndex, processedRequest, response, ex);  
            throw ex;  
        }  
        catch (Error err) {  
            ServletException ex = new NestedServletException("Handler processing failed", err);  
            // Trigger after-completion for thrown exception.  
            triggerAfterCompletion(mappedHandler, interceptorIndex, processedRequest, response, ex);  
            throw ex;  
        }  
  
        finally {  
            // Clean up any resources used by a multipart request.  
            if (processedRequest != request) {  
                cleanupMultipart(processedRequest);  
            }  
        }  
    }

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