docs: public T decodeContent(InputStream in, Charset charset) throws IOException {
          // 如果有内容
          if (getContentLength() > 0) {
              byte[] bytes = new byte[(int) getContentLength()];
              int contentSize = in.read(bytes);
              // 获取数据
              if (contentSize != getContentLength()) {
                  throw new IOException("读取到的数据长度与协议长度不符");
              }
              return FdfsParamMapper.map(bytes, genericType, charset);
          }
          return null;
      }