异步ajax验证用户名(防止重名)

<%@ WebHandler Language="C#" Class="Handler" %> using System; using System.Web; using System.Data; using DAL; public class Handler : IHttpHandler { public void ProcessRequest (HttpContext context) { context.Response.ContentType = "text/plain"; context.Response.Write("Hello World"); string username= context.Request.QueryString.Get("username"); if (username.ToString() == null || username.ToString() == "") { //禁止缓存 context.Response.Expires = -1;//相对过期时间 context.Response.ExpiresAbsolute = DateTime.Now.AddDays(-1);//绝对过期时间 context.Response.CacheControl = "no-cache"; context.Response.AddHeader("pragma", "no-cache"); context.Response.AddHeader("cache-control", "private"); string sql = string.Format("select * from MIS.JZG_REGISTER_TOTAL where USER_NAME='{0}'", username); DataTable ds = DBHelper.GetDataSet(sql); context.Response.Clear();//清除缓冲区流中所有内容 context.Response.Write("2"); context.Response.End(); }