分析Filter，HandlerInterceptor，ControllerAdvice，Aop的执行时机

测试代码 https://gitee.com/A_yes/pagehelper

Filter

因为filter不是springmvc里的，是servlet里的，所以filter在其他3个最外层

springboot中Filter的写法

//加了@Component注解，就不需要自己在配置类里去注册过滤器了
@Component
@WebServlet(urlPatterns = "/**")
public class MyFilter implements Filter {

    private static final Logger logger = LoggerFactory.getLogger(MyFilter.class);

    @Override
    public void init(FilterConfig filterConfig) throws ServletException {
        logger.warn(filterConfig.toString());
    }

    @Override
    public void doFilter(ServletRequest servletRequest, ServletResponse servletResponse, FilterChain filterChain) throws IOException, ServletException {
        logger.warn("Myfilter before");
        try {
            filterChain.doFilter(servletRequest,servletResponse);
        }catch (Throwable e){
            logger.error("Myfilter catch:{}",e.getMessage());
        }
        logger.warn("Myfilter after");
    }

    @Override
    public void destroy() {

    }
}

另外三个

剩下的三个就跟springmvc分不了关系了，我们一起来看看DispatcherServlet的关键方法doDispatch

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);
				
				//mappedHandle是一个HandlerExecutionChain对象，这个对象包含了要处理请求的handler和注册是拦截器们
				// Determine handler for the current request.
				mappedHandler = getHandler(processedRequest);
				if (mappedHandler == null) {
					noHandlerFound(processedRequest, response);
					return;
				}
				
				//通过HandlerExecutionChain对象中的handler找到一个合适的handler适配器  
				// 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 (new ServletWebRequest(request, response).checkNotModified(lastModified) && isGet) {
						return;
					}
				}

				//applyPreHandle方法就是循环调用们注册的拦截器的preHandle方法，
				//如果拦截器返回true，就接着执行下一个，
				//如果有返回false的，就结束执行,
				//并触发 triggerAfterCompletion 执行拦截器中的afterCompletion方法，请求也不会进入我们的handler
				if (!mappedHandler.applyPreHandle(processedRequest, response)) {
					return;
				}
				
				//这里开始调用我们的handler方法，一般为controller的方法
				//当调用的方法为我们aop的切点，那就会触发我们的aop执行
				//如果这里抛出异常，并且aop中没有进行捕获处理，那么就会进入我们的ControllerAdvice的异常处理方法
				// Actually invoke the handler.
				mv = ha.handle(processedRequest, response, mappedHandler.getHandler());

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

				applyDefaultViewName(processedRequest, mv);

				//执行我们注册的拦截器的postHandle方法，
				//可见如果我们的handler不能正常返回，是不会调用postHandle方法的
				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);
			}
			//在以上代码有异常未处理的时候会进入processHandlerException方法， 
			processDispatchResult(processedRequest, response, mappedHandler, mv, dispatchException);
		}
		catch (Exception ex) {
			triggerAfterCompletion(processedRequest, response, mappedHandler, ex);
		}
		catch (Throwable err) {
			triggerAfterCompletion(processedRequest, response, mappedHandler,
					new NestedServletException("Handler processing failed", err));
		}
		finally {
			if (asyncManager.isConcurrentHandlingStarted()) {
				// Instead of postHandle and afterCompletion
				if (mappedHandler != null) {
					mappedHandler.applyAfterConcurrentHandlingStarted(processedRequest, response);
				}
			}
			else {
				// Clean up any resources used by a multipart request.
				if (multipartRequestParsed) {
					cleanupMultipart(processedRequest);
				}
			}
		}
	}

//processHandlerException方法
protected ModelAndView processHandlerException(HttpServletRequest request, HttpServletResponse response,
			@Nullable Object handler, Exception ex) throws Exception {

		// Success and error responses may use different content types
		request.removeAttribute(HandlerMapping.PRODUCIBLE_MEDIA_TYPES_ATTRIBUTE);

		// Check registered HandlerExceptionResolvers...
		ModelAndView exMv = null;
		if (this.handlerExceptionResolvers != null) {
			for (HandlerExceptionResolver resolver : this.handlerExceptionResolvers) {
				//会在这里调用我们的ControllerAdvice的异常处理方法
				exMv = resolver.resolveException(request, response, handler, ex);
				if (exMv != null) {
					break;
				}
			}
		}
		if (exMv != null) {
			if (exMv.isEmpty()) {
				request.setAttribute(EXCEPTION_ATTRIBUTE, ex);
				return null;
			}
			// We might still need view name translation for a plain error model...
			if (!exMv.hasView()) {
				String defaultViewName = getDefaultViewName(request);
				if (defaultViewName != null) {
					exMv.setViewName(defaultViewName);
				}
			}
			if (logger.isTraceEnabled()) {
				logger.trace("Using resolved error view: " + exMv, ex);
			}
			if (logger.isDebugEnabled()) {
				logger.debug("Using resolved error view: " + exMv);
			}
			WebUtils.exposeErrorRequestAttributes(request, ex, getServletName());
			return exMv;
		}

		throw ex;
	}

拦截器的执行顺序

	boolean applyPreHandle(HttpServletRequest request, HttpServletResponse response) throws Exception {
		HandlerInterceptor[] interceptors = getInterceptors();
		if (!ObjectUtils.isEmpty(interceptors)) {
			//从第一个往后依次执行preHandle方法
			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;
	} 
	void applyPostHandle(HttpServletRequest request, HttpServletResponse response, @Nullable ModelAndView mv)
			throws Exception {

		HandlerInterceptor[] interceptors = getInterceptors();
		if (!ObjectUtils.isEmpty(interceptors)) {
			//从最后一个依次向前执行postHandle
			for (int i = interceptors.length - 1; i >= 0; i--) {
				HandlerInterceptor interceptor = interceptors[i];
				interceptor.postHandle(request, response, this.handler, mv);
			}
		}
	} 
	void triggerAfterCompletion(HttpServletRequest request, HttpServletResponse response, @Nullable Exception ex)
			throws Exception {

		HandlerInterceptor[] interceptors = getInterceptors();
		if (!ObjectUtils.isEmpty(interceptors)) {
			for (int i = this.interceptorIndex; i >= 0; i--) {
				//从已执行preHandle方法的最后一个拦截器向前执行afterCompletion
				HandlerInterceptor interceptor = interceptors[i];
				try {
					interceptor.afterCompletion(request, response, this.handler, ex);
				}
				catch (Throwable ex2) {
					logger.error("HandlerInterceptor.afterCompletion threw exception", ex2);
				}
			}
		}
	}

总结