*.ashx文件不能访问Session值的解决方法

<%@ WebHandler Language="C#" Class="productHandler" %>
using System; 
using System.Web; 
using JBTCard.Entity.CompanyEntity; 
using JBTCard.Business.CompanyBS; 
using System.Collections.Generic; 
using Newtonsoft.Json; 
using System.Web.SessionState; 

public class productHandler : IHttpHandler, IRequiresSessionState, IReadOnlySessionState{ 
 
 public void ProcessRequest (HttpContext context) { 
 string moduleId = context.Request.Form["moduleId"].ToString(); 
 string message = ""; 
 switch (moduleId) 
 { 
 case "getPTypeList": 
 IList<ProductTypeIdNameEntity> list = ProductTypeBS.GetPTypeListIdName(); 
 message = JavaScriptConvert.SerializeObject(list); 
 break; 
 case "getCompanyById": 
int cid = Convert.ToInt32(context.Session["cid"]); CompanyEntity company = CompanyBS.GetCompanyEntyById(1); 
 message = JavaScriptConvert.SerializeObject(company); 
 break; 
 case "insert": 
 string condis = context.Request.Form["condi"].ToString(); 
 ProductEntity model = (ProductEntity)JavaScriptConvert.DeserializeObject(condis, typeof(ProductEntity)); 

 bool b = ProductBS.AddProduct(model); 
 if (b) 
 { 
 message = "{success:true}"; 
 } 
 else 
 { 
 throw new Exception("商品添加失败！"); 
 } 
break; 
 } 
 context.Response.ContentType = "text/javascript"; 
 context.Response.Write(message); 
 } 

 public bool IsReusable { 
 get { 
 return false; 
 } 
 } 
}

using System.Web.SessionState;