C#解析"a=1&b=2&c=3"字符串，微信支付返回字符串，替换<br>为&

<%@ WebHandler Language="C#" class="Default" %>

using System;
using System.Web;
using System.Text;
using System.Collections.Specialized;

public class Default : IHttpHandler {
    
    public void ProcessRequest (HttpContext context) {
        context.Response.ContentType = "text/plain";

        string str = "a=1&b=2&c=3";
        NameValueCollection query = HttpUtility.ParseQueryString(str, Encoding.GetEncoding("gb2312"));
        context.Response.Write(query["a"]);
    }

    public bool IsReusable {
        get {
            return false;
        }
    }

}

            resultDescription = resultDescription.Replace("<br>", "&");
            NameValueCollection query = HttpUtility.ParseQueryString(resultDescription, Encoding.GetEncoding("gb2312"));
            responseModel.MicroPayRequestModel = new Models.RequestModel.MicroPayRequestModel();
            responseModel.MicroPayRequestModel.Appid = query["appid"];
            responseModel.MicroPayRequestModel.XXX= query["XXX"];