code: public String getDefinedCacheKey(String keyEL, Object target, Object[] arguments, Object retVal, boolean hasRetVal)
              throws Exception {
          return this.getElValue(keyEL, target, arguments, retVal, hasRetVal, String.class);
      }
docs: 根据请求参数和执行结果值，进行构造缓存Key
  
  @param keyEL     生成缓存Key的表达式
  @param target    AOP 拦截到的实例
  @param arguments 参数
  @param retVal    结果值
  @param hasRetVal 是否有retVal
  @return CacheKey 缓存Key
  @throws Exception 异常