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开源框架中的责任链模式实践( 二 )

框架


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  • Spring中的拦截器(Interceptor) 用于拦截控制器方法的执行，可以在方法执行前后添加自定义逻辑类似于AOP编程思想 。
  • Inteceptor的作用时机是在请求（request）进入servlet后，在进入Controller之前进行预处理 。
  • Inteceptor的实际应用包括：认证授权、日志记录、字符编码转换，敏感词过滤等等 。
  • Inteceptor中责任链的实现会从处理器的介绍，责任链的构建以及责任链的执行三个角度进行阐述 。
3.1.2 处理器介绍
public interface HandlerInterceptor {boolean preHandle(HttpServletRequest request, HttpServletResponse response, Object handler) throws Exception;void postHandle(HttpServletRequest request, HttpServletResponse response, Object handler, ModelAndView modelAndView) throws Exception;void afterCompletion(HttpServletRequest request, HttpServletResponse response, Object handler, Exception ex) throws Exception;} @Componentpublic class TimeInterceptor extends HandlerInterceptorAdapter {@Overridepublic boolean preHandle(HttpServletRequest request, HttpServletResponse response, Object handler) throws Exception {// 前置处理System.out.println("time interceptor preHandle");return true;}@Overridepublic void postHandle(HttpServletRequest request, HttpServletResponse response, Object handler, ModelAndView modelAndView) throws Exception {// 后置处理System.out.println("time interceptor postHandle");}@Overridepublic void afterCompletion(HttpServletRequest request, HttpServletResponse response, Object handler, Exception ex) throws Exception {System.out.println("time interceptor afterCompletion");}}说明：
  • 处理器Interceptor的接口HandlerInterceptor定义了三个方法，可在控制器方法执行前后添加自定义逻辑 。
  • 自定义处理器如上的TimeInterceptor需要自定义实现上述3个方法实现自我的逻辑 。
  • 所有的自定义处理会串联在HandlerExecutionChain类实现的责任链上 。
3.1.3 责任链构建
public class HandlerExecutionChain {private final Object handler;private HandlerInterceptor[] interceptors;private List<HandlerInterceptor> interceptorList;private int interceptorIndex = -1;public void addInterceptor(HandlerInterceptor interceptor) {// 添加拦截器initInterceptorList().add(interceptor);}public void addInterceptors(HandlerInterceptor... interceptors) {if (!ObjectUtils.isEmpty(interceptors)) {CollectionUtils.mergeArrayIntoCollection(interceptors, initInterceptorList());}}private List<HandlerInterceptor> initInterceptorList() {if (this.interceptorList == null) {this.interceptorList = new ArrayList<HandlerInterceptor>();if (this.interceptors != null) {// An interceptor array specified through the constructorCollectionUtils.mergeArrayIntoCollection(this.interceptors, this.interceptorList);}}this.interceptors = null;return this.interceptorList;}}说明：
  • HandlerExecutionChain类作为串联Interceptor处理器的责任链负责责任链的构建和执行 。
  • HandlerExecutionChain类通过集合对象interceptorList保存所有相关的处理器对象 。
3.1.4 责任链执行
public class DispatcherServlet extends FrameworkServlet {protected void doDispatch(HttpServletRequest request, HttpServletResponse response) throws Exception {try {try {// mappedHandler代表的是HandlerExecutionChain责任链mappedHandler = getHandler(processedRequest);HandlerAdapter ha = getHandlerAdapter(mappedHandler.getHandler());// 1、执行mappedHandler的applyPreHandle方法if (!mappedHandler.applyPreHandle(processedRequest, response)) {return;}// 2、执行controller的执行逻辑mv = ha.handle(processedRequest, response, mappedHandler.getHandler());if (asyncManager.isConcurrentHandlingStarted()) {return;}applyDefaultViewName(processedRequest, mv);// 执行mappedHandler的applyPostHandle方法mappedHandler.applyPostHandle(processedRequest, response, mv);}catch (Exception ex) {}processDispatchResult(processedRequest, response, mappedHandler, mv, dispatchException);}catch (Exception ex) {}finally {}}}public class HandlerExecutionChain {private final Object handler;private HandlerInterceptor[] interceptors;private List<HandlerInterceptor> interceptorList;private int interceptorIndex = -1;boolean applyPreHandle(HttpServletRequest request, HttpServletResponse response) throws Exception {HandlerInterceptor[] interceptors = getInterceptors();if (!ObjectUtils.isEmpty(interceptors)) {// 责任链从前往后的顺序执行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, ModelAndView mv) throws Exception {HandlerInterceptor[] interceptors = getInterceptors();if (!ObjectUtils.isEmpty(interceptors)) {// 责任链从后往前的顺序执行for (int i = interceptors.length - 1; i >= 0; i--) {HandlerInterceptor interceptor = interceptors[i];interceptor.postHandle(request, response, this.handler, mv);}}}}


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