IHttpHandler Session

　　今天在工作编写代码时，在IHttpHandler的父类中使用了Session，在后台代码中调用该Session，但是抛出异常说该Session是Null，在网上查询相关资料说必须继承借口：IReadOnlySessionState 或 IRequiresSessionState，必须应用System.Web.SessionState命名空间

　　IHttpHandler:　

　　 // Summary:
    //     Defines the contract that ASP.NET implements to synchronously process HTTP
    //     Web requests using custom HTTP handlers.
    public interface IHttpHandler
    {
        // Summary:
        //     Gets a value indicating whether another request can use the System.Web.IHttpHandler
        //     instance.
        //
        // Returns:
        //     true if the System.Web.IHttpHandler instance is reusable; otherwise, false.
        bool IsReusable { get; }

        // Summary:
        //     Enables processing of HTTP Web requests by a custom HttpHandler that implements
        //     the System.Web.IHttpHandler interface.
        //
        // Parameters:
        //   context:
        //     An System.Web.HttpContext object that provides references to the intrinsic
        //     server objects (for example, Request, Response, Session, and Server) used
        //     to service HTTP requests.
        void ProcessRequest(HttpContext context);
    }

　　IReadOnlySessionState:表示Http handler能够读取Session的值

    // Summary:
    //     Specifies that the target HTTP handler requires only read access to session-state
    //     values. This is a marker interface and has no methods.
    public interface IReadOnlySessionState : IRequiresSessionState
    {
    }

　　IRequiresSessionState:表示Http handler能够读写Session的值

    // Summary:
    //     Specifies that the target HTTP handler requires read and write access to
    //     session-state values. This is a marker interface and has no methods.
    public interface IRequiresSessionState
    {
    }

　　将继承IHttpHandler的类同时实现IRequiresSessionState 或 IReadOnlySessionState，即可使用Session,如下所示：

　　public class TestHandler : IHttpHandler, IRequiresSessionState
    {
        public void ProcessRequest(HttpContext context)
        {
            context.Response.ContentType = "text/plain";
            context.Session["TestSession = "TestSession";
            context.Response.Write("Hello World");
        }

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

即可解决IHttpHandler不能使用Session问题