ashx 接受 post json 请求
HttpContext.Current.Response.ContentType = "application/json";
HttpContext.Current.Response.ContentEncoding = Encoding.UTF8;
Stream inputStream = HttpContext.Current.Request.InputStream;
Encoding encoding = HttpContext.Current.Request.ContentEncoding;
StreamReader streamReader = new StreamReader(inputStream, encoding);
string strJson = streamReader.ReadToEnd();