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SpringMVC的拦截器不同于Spring的拦截器，SpringMVC具有统一的入口DispatcherServlet，所有的请求都通过DispatcherServlet，所以只需要在DispatcherServlet上做文章即可，DispatcherServlet也没有代理，同时SpringMVC管理的Controller也不有代理。哪不难想到我们在执行controller之前做某些动作，执行完毕做某些动作，render完成做某些动作。SpringMVC的拦截器对应提供了三个preHandle，postHandle，afterCompletion方法。只需在三个方法内写我们需要的逻辑就行，多了都是废话，还是代码实在

HandlerInterceptor[] interceptors = mappedHandler.getInterceptors();				if (interceptors != null) {					for (int i = 0; i < interceptors.length; i++) {						HandlerInterceptor interceptor = interceptors[i];//ha.handle是调用具体的controller在此之前执行preHandle						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());

  完成调用之后，调用render(),最后执行afterCompletion()

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);

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