post请求json内容丢失问题

今天在项目组用json传输数据 post方法提交发现传输过去的数据json内的+ 号被直接干掉了.
后来传输之前直接先编码.
接收端:
 1   public void ProcessRequest(HttpContext context)
 2         {
 3             ReturnResult result = new ReturnResult();
 4             var method = context.Request.QueryString["method"].ToString();
 5 
 6             byte[] byts = new byte[HttpContext.Current.Request.InputStream.Length];
 7             HttpContext.Current.Request.InputStream.Read(byts, 0, byts.Length);
 8             string req = System.Text.Encoding.Default.GetString(byts);
 9             req = HttpContext.Current.Server.UrlDecode(req);
10 
11 
12             //string p = @"d{4}-d{2}-d{2}sd{2}:d{2}:d{2}";
13             //MatchEvaluator matchEvaluator = new MatchEvaluator(ConvertDateStringToJsonDate);
14             //Regex reg = new Regex(p);
15             //req = reg.Replace(req, matchEvaluator);
16 
17 
18             try
19             {
20                 if (context.Request.Params.Count > 0)
21                 {
22 
23                     if (!string.IsNullOrEmpty(method))
24                     {
25                         switch (method)
26                         {
27 
28                             case DTKeys.URL_PARM_METHOD_SENDMESSAGEREMIND://来自用户信息认证的 附件上传
29                                 ContactMsg m = JsonHelper.FromJson<ContactMsg>(req);
30                                 SendMessageRemind(m);
31                                 break;
32 
33                             default:
34                                 break;
35                         }
36                     }
37                 }
38                 else
39                 {
40                     result.Status = false;
41                     result.Msg = "未检测的有效文件信息,或者您未登录";
42                 }
43             }
44             catch (Exception ex)
45             {
46                 result.Status = false;
47                 result.Msg = ex.Message;
48                 Log4netHelper.WriteExceptionLog("Beta.ProductMarket.Web.Product.SendMsgToWX.ashx", ex);
49             }
50             context.Response.Clear();
51             context.Response.ContentType = "text/html; charset=utf-8";
52             context.Response.Write(JsonConvert.SerializeObject(result));
53         }
54