Session is null in ashx handler解决办法

<% @ webhandler language="C#" class="DownloadHandler" %>

using System;
using System.Web;
using System.Web.SessionState;

public class DownloadHandler : IHttpHandler, IReadOnlySessionState
{
   public bool IsReusable { get { return true; } }
   
   public void ProcessRequest(HttpContext ctx)
   {
       ctx.Response.Write(ctx.Session["hello"]);
   }
}