code: public static SerializeHandler getHandlerByProtocal(String protocol)
              throws InvalidProtocolException {
          SerializeHandler handler = HANDLER_MAP.get(protocol);
          if (handler != null) {
              return handler;
          }
          throw new InvalidProtocolException("rpc protocol not supported for " + protocol);
      }
docs: 根据http请求中的content-type尝试寻找序列化handler
  
  @param protocol
  @return
  @throws InvalidProtocolException