c#和java base64不一致的解决方法

{"contentType":"","httpMethod":"POST","paramMap":"{\"keyword\":\"华为\"}","url":"https:\/\/bizapi.jd.com\/api\/search\/search"} --第一条

{"contentType":"","httpMethod":"POST","paramMap":{"keyword":"华为"},"url":"https://bizapi.jd.com/api/search/search"}  ----第二条

using Newtonsoft.Json;
using System;
using System.Collections.Generic;
using System.ComponentModel;
using System.Data;
using System.Drawing;
using System.Linq;
using System.Text;
using System.Windows.Forms;

namespace Base64
{
 public partial class Form1 : Form
 {
  public Form1()
  {
   InitializeComponent();
  }

  
  private void button1_Click(object sender, EventArgs e)
  {
   Dictionary<string, string> dic = new Dictionary<string, string>();
   dic.Add("Cid", "123456"); dic.Add("type", "int");
   JsonStr jsonstr=new JsonStr(dic,"http://localhost");
   string result = JavaBase64(JsonConvert.SerializeObject(jsonstr));
  }


  #region 实体类
  /// <summary>
  /// 实体类
  /// </summary>
  class JsonStr
  {
   public string Method = "POST";
   public Dictionary<string, string> param;
   public string url = "";
   public JsonStr(Dictionary<string, string> _param, string _url)
   {
    param = _param; url = _url;
   }
  } 
  #endregion


  #region 转换为单字节 java base64
  /// <summary>
  /// 转换为单字节 java base64
  /// </summary>
  /// <param name="str"></param>
  /// <returns></returns>
  public static string JavaBase64(string str)
  {
   byte[] by = Encoding.UTF8.GetBytes(str);
   sbyte[] sby = new sbyte[by.Length];
   for (int i = 0; i < by.Length; i++)
   {
    if (by[i] > 127)
     sby[i] = (sbyte)(by[i] - 256);
    else
     sby[i] = (sbyte)by[i];
   }
   byte[] newby = (byte[])(object)sby;
   return Convert.ToBase64String(newby);
  } 
  #endregion



 }
}

{"contentType":"","httpMethod":"POST","paramMap":"{\"keyword\":\"华为\"}","url":"https:\/\/bizapi.jd.com\/api\/search\/search"}