code: private CacheKeyTO getCacheKey(CacheAopProxyChain pjp, Object[] arguments, ExCache exCache, Object result) {
          Object target = pjp.getTarget();
          String methodName = pjp.getMethod().getName();
          String keyExpression = exCache.key();
          if (null == keyExpression || keyExpression.trim().length() == 0) {
              return null;
          }
          String hfieldExpression = exCache.hfield();
          return getCacheKey(target, methodName, arguments, keyExpression, hfieldExpression, result, true);
      }
docs: 生成缓存 Key
  
  @param pjp
  @param arguments
  @param exCache
  @param result    执行结果值
  @return 缓存Key