1.監視器

　　(1)首先監視器是觀察者模式的實現，在我之前的博客中有關于監視器模式的解釋。監視器相當于觀察者

　　(2)我們在springMvc中最常見的監視器 ContextLoaderlistener

<listener><listener-class>org.springframework.web.context.ContextLoaderListener</listener-class></listener>

　?? (3)我們來看看ContextLiaderListener（當某件事情發生后，調用這個方法來初始化spring父容器與springMvc子容器）

　　　

@Overridepublic void contextInitialized(ServletContextEvent event) {initWebApplicationContext(event.getServletContext()); }

2.過濾器與攔截器(過濾器與攔截器相似，只是作用的地方不同)

　　(1).在之前的博客中說過Servlet的service方法是在ApplicationFilterChain中。我們來看看這個類中的方法

private void internalDoFilter(ServletRequest request,ServletResponse response)throws IOException, ServletException {// Call the next filter if there is oneif (pos < n) {ApplicationFilterConfig filterConfig = filters[pos++];try {Filter filter = filterConfig.getFilter();if (request.isAsyncSupported() && "false".equalsIgnoreCase(filterConfig.getFilterDef().getAsyncSupported())) {request.setAttribute(Globals.ASYNC_SUPPORTED_ATTR, Boolean.FALSE);}if( Globals.IS_SECURITY_ENABLED ) {final ServletRequest req = request;final ServletResponse res = response;Principal principal =((HttpServletRequest) req).getUserPrincipal();Object[] args = new Object[]{req, res, this};SecurityUtil.doAsPrivilege ("doFilter", filter, classType, args, principal);} else {filter.doFilter(request, response, this); //在這里調用了過濾器的doFilter()方法}} catch (IOException | ServletException | RuntimeException e) {throw e;} catch (Throwable e) {e = ExceptionUtils.unwrapInvocationTargetException(e);ExceptionUtils.handleThrowable(e);throw new ServletException(sm.getString("filterChain.filter"), e);}return;}// We fell off the end of the chain -- call the servlet instancetry {if (ApplicationDispatcher.WRAP_SAME_OBJECT) {lastServicedRequest.set(request);lastServicedResponse.set(response);}if (request.isAsyncSupported() && !servletSupportsAsync) {request.setAttribute(Globals.ASYNC_SUPPORTED_ATTR,Boolean.FALSE);}// Use potentially wrapped request from this pointif ((request instanceof HttpServletRequest) &&(response instanceof HttpServletResponse) &&Globals.IS_SECURITY_ENABLED ) {final ServletRequest req = request;final ServletResponse res = response;Principal principal =((HttpServletRequest) req).getUserPrincipal();Object[] args = new Object[]{req, res};SecurityUtil.doAsPrivilege("service",servlet,classTypeUsedInService,args,principal);} else {servlet.service(request, response); //在這里調用service方法}} catch (IOException | ServletException | RuntimeException e) {throw e;} catch (Throwable e) {e = ExceptionUtils.unwrapInvocationTargetException(e);ExceptionUtils.handleThrowable(e);throw new ServletException(sm.getString("filterChain.servlet"), e);} finally {if (ApplicationDispatcher.WRAP_SAME_OBJECT) {lastServicedRequest.set(null);lastServicedResponse.set(null);}}}

?也就是說我們的過濾器的doFilter()方法是在Servlet的service方法之前調用的。

(2)我們再來看看攔截器

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.mappedHandler = getHandler(processedRequest);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()) {logger.debug("Last-Modified value for [" + getRequestUri(request) + "] is: " + lastModified);}if (new ServletWebRequest(request, response).checkNotModified(lastModified) && isGet) {return;}}if (!mappedHandler.applyPreHandle(processedRequest, response)) {　　　　　//在這里調用了攔截器中的preHandler()方法return;}// Actually invoke the handler.mv = ha.handle(processedRequest, response, mappedHandler.getHandler()); //在這里調用Controller中的方法if (asyncManager.isConcurrentHandlingStarted()) {return;}applyDefaultViewName(processedRequest, mv);mappedHandler.applyPostHandle(processedRequest, response, mv);　　　　　　　　//在這里調用了攔截器的postHandler()方法}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);}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 afterCompletionif (mappedHandler != null) {mappedHandler.applyAfterConcurrentHandlingStarted(processedRequest, response);}}else {// Clean up any resources used by a multipart request.if (multipartRequestParsed) {cleanupMultipart(processedRequest);}}}}

也就是說攔截器的方法是在controller中的方法調用前后被調用的。

3.總結：

　　(1)監聽器是觀察者模式的實現

　　(2)過濾器與攔截器相似，只不過過濾器是在service()方法被調用前調用的，而攔截器是在Controller中的方法被調用前調用的。

轉載于:https://www.cnblogs.com/liwangcai/p/10744091.html

總結

以上是生活随笔為你收集整理的spring中的监视器，过滤器，拦截器的全部內容，希望文章能夠幫你解決所遇到的問題。

如果覺得生活随笔網站內容還不錯，歡迎將生活随笔推薦給好友。