对handlerexecutionchain类的深入理解

/* * 处理器执行链由处理器对象和拦截器组成。 */public class HandlerExecutionChain {

private final Object handler; //处理器对象。  private HandlerInterceptor[] interceptors; //拦截器数组  private List<HandlerInterceptor> interceptorList; //拦截器列表

/**   * Apply preHandle methods of registered interceptors.   * @return {@code true} if the execution chain should proceed with the   * next interceptor or the handler itself. Else, DispatcherServlet assumes   * that this interceptor has already dealt with the response itself.   * 执行已经注册的拦截的 preHandle()方法。如果返回true,则执行链可以执行下一个拦截器的preHandle()方法或 handler 自身。   * 否则，   */  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;  }

/*   * 执行已经注册的拦截器 postHandle()方法。   */  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);      }    }  }

/**   * 这个方法只会执行preHandle()方法已经成功执行并且返回true的拦截器中的postHandle()方法。   */  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);        }      }    }  }