前言:这两天学习了代理模式,自然想到了 springmvc 的 aop 使用的就是动态代理,拦截器使用的就是 jdk 的动态代理。今天看了看源码,记录一下。转载请注明出处:https://www.cnblogs.com/yuxiaole/p/9969360.html
springMVC 的拦截器使用移步:Java Servlet 过滤器与 springmvc 拦截器的区别?
源码解析
springMVC 的所有连接入口都会进入 DispatcherServlet,然后在这里面去调用真正的 Controller。而拦截器要达到的作用则是在调用 Controller 前后去做一些事情。所以现在需要看看 DispatcherServlet 的源码。
DispatcherServlet
DispatcherServlet 的源码入口在 doService() 方法。
protected void doService(HttpServletRequest request, HttpServletResponse response) throws Exception { if(this.logger.isDebugEnabled()) { String resumed = WebAsyncUtils.getAsyncManager(request).hasConcurrentResult()?" resumed":""; this.logger.debug("DispatcherServlet with name '" + this.getServletName() + "'" + resumed + " processing " + request.getMethod() + " request for [" + getRequestUri(request) + "]"); } Map<String, Object> attributesSnapshot = null; if(WebUtils.isIncludeRequest(request)) { attributesSnapshot = new HashMap(); Enumeration attrNames = request.getAttributeNames(); label108: while(true) { String attrName; do { if(!attrNames.hasMoreElements()) { break label108; } attrName = (String)attrNames.nextElement(); } while(!this.cleanupAfterInclude && !attrName.startsWith("org.springframework.web.servlet")); attributesSnapshot.put(attrName, request.getAttribute(attrName)); } } request.setAttribute(WEB_APPLICATION_CONTEXT_ATTRIBUTE, this.getWebApplicationContext()); request.setAttribute(LOCALE_RESOLVER_ATTRIBUTE, this.localeResolver); request.setAttribute(THEME_RESOLVER_ATTRIBUTE, this.themeResolver); request.setAttribute(THEME_SOURCE_ATTRIBUTE, this.getThemeSource()); FlashMap inputFlashMap = this.flashMapManager.retrieveAndUpdate(request, response); if(inputFlashMap != null) { request.setAttribute(INPUT_FLASH_MAP_ATTRIBUTE, Collections.unmodifiableMap(inputFlashMap)); } request.setAttribute(OUTPUT_FLASH_MAP_ATTRIBUTE, new FlashMap()); request.setAttribute(FLASH_MAP_MANAGER_ATTRIBUTE, this.flashMapManager); try { this.doDispatch(request, response); } finally { if(!WebAsyncUtils.getAsyncManager(request).isConcurrentHandlingStarted() && attributesSnapshot != null) { this.restoreAttributesAfterInclude(request, attributesSnapshot); } } }
doService() 方法里面处理了一些信息之后,调用了 doDispatch() 方法。
protected void doDispatch(HttpServletRequest request, HttpServletResponse response) throws Exception { HttpServletRequest processedRequest = request; HandlerExecutionChain mappedHandler = null; boolean multipartRequestParsed = false; WebAsyncManager asyncManager = WebAsyncUtils.getAsyncManager(request); try { try { ModelAndView mv = null; Object dispatchException = null; try { processedRequest = this.checkMultipart(request); multipartRequestParsed = processedRequest != request; mappedHandler = this.getHandler(processedRequest); if(mappedHandler == null || mappedHandler.getHandler() == null) { this.noHandlerFound(processedRequest, response); return; } HandlerAdapter ha = this.getHandlerAdapter(mappedHandler.getHandler()); String method = request.getMethod(); boolean isGet = "GET".equals(method); if(isGet || "HEAD".equals(method)) { long lastModified = ha.getLastModified(request, mappedHandler.getHandler()); if(this.logger.isDebugEnabled()) { this.logger.debug("Last-Modified value for [" + getRequestUri(request) + "] is: " + lastModified); } if((new ServletWebRequest(request, response)).checkNotModified(lastModified) && isGet) { return; } } if(!mappedHandler.applyPreHandle(processedRequest, response)) { return; } mv = ha.handle(processedRequest, response, mappedHandler.getHandler()); if(asyncManager.isConcurrentHandlingStarted()) { return; } this.applyDefaultViewName(processedRequest, mv); mappedHandler.applyPostHandle(processedRequest, response, mv); } catch (Exception var20) { dispatchException = var20; } catch (Throwable var21) { dispatchException = new NestedServletException("Handler dispatch failed", var21); } this.processDispatchResult(processedRequest, response, mappedHandler, mv, (Exception)dispatchException); } catch (Exception var22) { this.triggerAfterCompletion(processedRequest, response, mappedHandler, var22); } catch (Throwable var23) { this.triggerAfterCompletion(processedRequest, response, mappedHandler, new NestedServletException("Handler processing failed", var23)); } } finally { if(asyncManager.isConcurrentHandlingStarted()) { if(mappedHandler != null) { mappedHandler.applyAfterConcurrentHandlingStarted(processedRequest, response); } } else if(multipartRequestParsed) { this.cleanupMultipart(processedRequest); } } }
doDispatch() 方法中通过 this.getHandler(processedRequest); 获取到了处理器链 HandlerExecutionChain mappedHandle 之后,去执行了 mappedHandler.applyPreHandle(processedRequest, response) 方法,从而执行了拦截器的 preHandle 方法,如果返回为 false,则会调用处理器链的 triggerAfterCompletion 方法,然后 DispatchServlet 类中会直接 retreturn;如果返回为 true,则继续。
然后调用了 HandlerAdapter 的 handler() 方法;
然后调用了 mappedHandler.applyPostHandle(processedRequest, response, mv); 方法,从而执行了拦截器的 postHandle 方法;
然后调用了 this.processDispatchResult(processedRequest, response, mappedHandler, mv, (Exception)dispatchException); 方法;在 processDispatchResult() 方法里面渲染了对应的视图,然后调用了 mappedHandler.triggerAfterCompletion(request, response, (Exception)null); 方法,从而执行了拦截器的 afterCompletion 方法。
processDispatchResult() 源码如下:
private void processDispatchResult(HttpServletRequest request, HttpServletResponse response, HandlerExecutionChain mappedHandler, ModelAndView mv, Exception exception) throws Exception { boolean errorView = false; if(exception != null) { if(exception instanceof ModelAndViewDefiningException) { this.logger.debug("ModelAndViewDefiningException encountered", exception); mv = ((ModelAndViewDefiningException)exception).getModelAndView(); } else { Object handler = mappedHandler != null?mappedHandler.getHandler():null; mv = this.processHandlerException(request, response, handler, exception); errorView = mv != null; } } if(mv != null && !mv.wasCleared()) { this.render(mv, request, response); if(errorView) { WebUtils.clearErrorRequestAttributes(request); } } else if(this.logger.isDebugEnabled()) { this.logger.debug("Null ModelAndView returned to DispatcherServlet with name '" + this.getServletName() + "': assuming HandlerAdapter completed request handling"); } if(!WebAsyncUtils.getAsyncManager(request).isConcurrentHandlingStarted()) { if(mappedHandler != null) { mappedHandler.triggerAfterCompletion(request, response, (Exception)null); } } }
从 doDispatch() 方法这里主要需要知道 HandlerExecutionChain mappedHandler = this.getHandler(processedRequest); 这一句调用的 getHandler() 方法,源码如下。
getHandle() 方法里是通过 HandlerMapping 的 getHandler 方法返回 HandlerExecutionChain 的。
从代码中不难看出整个逻辑就是依次判断 servlet 中的每个 handlerMapping 是否能够匹配该请求,直到找到那个匹配的然后返回处理结果。
protected HandlerExecutionChain getHandler(HttpServletRequest request) throws Exception { Iterator var2 = this.handlerMappings.iterator(); HandlerExecutionChain handler; do { if(!var2.hasNext()) { return null; } HandlerMapping hm = (HandlerMapping)var2.next(); if(this.logger.isTraceEnabled()) { this.logger.trace("Testing handler map [" + hm + "] in DispatcherServlet with name '" + this.getServletName() + "'"); } handler = hm.getHandler(request); } while(handler == null); return handler; }
HandlerExecutionChain 类
applyPreHandle() 方法源码如下:可以看出是顺序调用拦截器的 preHandle() 方法。preHandle 返回 false 时调用了 triggerAfterCompletion 方法。
boolean applyPreHandle(HttpServletRequest request, HttpServletResponse response) throws Exception { HandlerInterceptor[] interceptors = this.getInterceptors(); if(!ObjectUtils.isEmpty(interceptors)) { for(int i = 0; i < interceptors.length; this.interceptorIndex = i++) { HandlerInterceptor interceptor = interceptors[i]; if(!interceptor.preHandle(request, response, this.handler)) { this.triggerAfterCompletion(request, response, (Exception)null); return false; } } } return true; }
applyPostHandle() 方法源码如下:可以看出这里是逆序调用 postHandle 方法。
void applyPostHandle(HttpServletRequest request, HttpServletResponse response, ModelAndView mv) throws Exception { HandlerInterceptor[] interceptors = this.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); } } }
triggerAfterCompletion() 方法源码如下:可以看出这里也是逆序调用 afterCompletion 方法。
void triggerAfterCompletion(HttpServletRequest request, HttpServletResponse response, Exception ex) throws Exception { HandlerInterceptor[] interceptors = this.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 var8) { logger.error("HandlerInterceptor.afterCompletion threw exception", var8); } } } }
转载请注明出处:https://www.cnblogs.com/yuxiaole/p/9969360.html