SpringFramework之HandlerInterceptor-白红宇

SpringFramework之HandlerInterceptor

阅读量：5772 次

发布时间：2019-06-18

本文共 5868 字，大约阅读时间需要 19 分钟。

最近在使用Spring时，总感觉对HandlerInterceptor有点模糊，回头再来看看，记录下。

SpringFramework的版本4.3.x.RELEASE.

List-1

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);			// Determine handler for the current request.			//1、得到handlerExecutionChain，里面含有对应的Controller,里面还有interceptor，			mappedHandler = getHandler(processedRequest);			if (mappedHandler == null || mappedHandler.getHandler() == null) {				noHandlerFound(processedRequest, response);				return;			}			// Determine handler adapter for the current request.			//2、会根据Controller方法上的注解，将request中的请求转换为对象，转换为对应的pathVariable、body等			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;				}			}            //3、			if (!mappedHandler.applyPreHandle(processedRequest, response)) {				return;			}			// Actually invoke the handler.			//4、真正进行反射操作，调用方法			mv = ha.handle(processedRequest, response, mappedHandler.getHandler());			if (asyncManager.isConcurrentHandlingStarted()) {				return;			}			applyDefaultViewName(processedRequest, mv);            //5、			mappedHandler.applyPostHandle(processedRequest, response, mv);		}		catch (Exception ex) {			dispatchException = ex;		}		catch (Throwable err) {			// As of 4.3, we're processing Errors thrown from handler methods as well,			// making them available for @ExceptionHandler methods and other scenarios.			dispatchException = new NestedServletException("Handler dispatch failed", err);		}		//6		processDispatchResult(processedRequest, response, mappedHandler, mv, dispatchException);	}	catch (Exception ex) {	    //7		triggerAfterCompletion(processedRequest, response, mappedHandler, ex);	}	catch (Throwable err) {	    //8		triggerAfterCompletion(processedRequest, response, mappedHandler,				new NestedServletException("Handler processing failed", err));	}

如List-1所示，

1位置，根据ServletRequest得到HandlerExecutionChain(具体怎么得到的有点复杂，后续再深入分析)，它有点类似SpringSecurity中的FilterChainProxy。里面有HandlerInterceptor数组，和handler属性(通过debug可以看到是HandlerMethod)。

2位置，会根据Controller方法上的注解，将request中的请求转换为对象，转换为对应的pathVariable、body等。

3位置，调用HandlerExecutionChain的applyPreHandle，如下，逐个调用preHandle方法，只要preHandle返还false，就会你像调用afterCompletion，最后返还false。思考，通过源码可知在HandlerInterceptor中拦截后续preHandle中抛出的异常是拦截不到的。这个HandlerExceptionChain是线程安全的，每个请求对应一个HandlerExceptionChain实例对象，所以源码中通过类属性interceptorIndex来控制下标。

List-2

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;}

位置4，到位置4，已经执行了所有handlerInterceptor的preHandle，并且已经将ServletRequest中的参数转换为了Controller方法上标有注解的参数。所以在位置通过反射调用Controller的方法。通过源码可以看出，HandlerInterceptor可以看出，只要Controller里面的业务代码抛出异常，那么位置5就执行不到，就不会执行HandlerInterceptor的postHandle方法。

位置5，如下List-3所示，会逆向执行HandlerInterceptor的postHandle方法。

List-3

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);		}	}}

位置6、如果之前没有抛出异常，就调用processDispatchResult方法，方法processDispatchResult的最后，有如下List-4，调用HandlerExecutionChain的triggerAfterCompletion，会逆序调用HandlerInterceptor的afterCompletion，由List-5可以看出，afterCompletion中抛出异常，会被Spring框架吞噬，每个HandlerInterceptor的afterCompletion方法中，拿到的异常都是null——看List-4中传入的参数。

List-4

......	if (mappedHandler != null) {		mappedHandler.triggerAfterCompletion(request, response, null);	}}

List-5

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);			}		}	}}