微信 编码要UTF8

<%@ WebHandler Language="C#" Class="Handler" %>

using System;
using System.Collections.Generic;
using System.Web;
using System.IO;
using System.Text;
using System.Web.Security;
using System.Xml;

public class Handler : IHttpHandler
{

    public void ProcessRequest(HttpContext param_context)
    {

        string postString = string.Empty;
        if (HttpContext.Current.Request.HttpMethod.ToUpper() == "POST")
        {
            using (Stream stream = HttpContext.Current.Request.InputStream)
            {
                Byte[] postBytes = new Byte[stream.Length];
                stream.Read(postBytes, , (Int32)stream.Length);
                postString = Encoding.Default.GetString(postBytes);
            }

            if (!string.IsNullOrEmpty(postString))
            {
                Handle(postString);
            }
        }
        else
        {
            InterfaceTest();
        }
    }

    public bool IsReusable
    {
        get
        {
            return false;
        }
    }
    //写入日志
    public void WriteLog(string text)
    {
        StreamWriter sw = new StreamWriter(HttpContext.Current.Server.MapPath(".") + "\\log.txt", true);
        sw.WriteLine(text);
        sw.Close();//写入
    }

    /// <summary>
    /// 处理信息并应答
    /// </summary>
    private void Handle(string postStr)
    {
        WriteLog(postStr);        //记录微信服务器post字串
        messageHelper help = new messageHelper();
        string responseContent = help.ReturnMessage(postStr);
        HttpContext.Current.Response.ContentEncoding = Encoding.UTF8;
        HttpContext.Current.Response.Write(responseContent);
        WriteLog(responseContent);   //记录返回微信服务器字串

    }

    //成为开发者url测试，返回echoStr
    public void InterfaceTest()
    {
        string token = "填写的token";
        if (string.IsNullOrEmpty(token))
        {
            return;
        }

        string echoString = HttpContext.Current.Request.QueryString["echoStr"];
        string signature = HttpContext.Current.Request.QueryString["signature"];
        string timestamp = HttpContext.Current.Request.QueryString["timestamp"];
        string nonce = HttpContext.Current.Request.QueryString["nonce"];

        if (!string.IsNullOrEmpty(echoString))
        {
            HttpContext.Current.Response.Write(echoString);
            HttpContext.Current.Response.End();
        }
    }

}