对handlerexecutionchain类的深入理解

HandlerExecutionChain类比较简单，好理解。

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

下面是类的部分属性。

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);
        }
      }
    }
  }

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