我有一个情况,就像在这篇文章中描述的那样:
我怎么能得到一个会话变量的值在c#中的静态方法?
但是,这里没有静态方法(只是从IHttpHandler继承的类)
下面是我的代码:<%@ WebHandler Language="C#" Class="Telerik.Web.Examples.FileExplorer.FilterAndDownloadFiles.Handler" %>
using System;
using System.Data;
using System.Configuration;
using System.Web;
using System.Text;
using Telerik.Web.UI;
namespace Telerik.Web.Examples.FileExplorer.FilterAndDownloadFiles
{
[RadCompressionSettings(HttpCompression = CompressionType.None)] // Disable RadCompression for this page ;
public class Handler : IHttpHandler
{
#region IHttpHandler Members
private HttpContext _context;
private HttpContext Context
{
get
{
return _context;
}
set
{
_context = value;
}
}
public void ProcessRequest(HttpContext context)
{
Context = context;
string filePath = context.Request.QueryString["path"];
filePath = context.Server.MapPath(filePath);
if (filePath == null)
{
return;
}
System.IO.StreamReader streamReader = new System.IO.StreamReader(filePath);
System.IO.BinaryReader br = new System.IO.BinaryReader(streamReader.BaseStream);
byte[] bytes = new byte[streamReader.BaseStream.Length];
br.Read(bytes, 0, (int)streamReader.BaseStream.Length);
if (bytes == null)
{
return;
}
streamReader.Close();
br.Close();
string fileName = System.IO.Path.GetFileName(filePath);
string MimeType = GetMimeType(fileName);
string extension = System.IO.Path.GetExtension(filePath);
char[] extension_ar = extension.ToCharArray();
string extension_Without_dot = string.Empty;
for (int i = 1; i < extension_ar.Length; i++)
{
extension_Without_dot += extension_ar[i];
}
//if (extension == ".jpg")
//{ // Handle *.jpg and
// WriteFile(bytes, fileName, "image/jpeg jpeg jpg jpe", context.Response);
//}
//else if (extension == ".gif")
//{// Handle *.gif
// WriteFile(bytes, fileName, "image/gif gif", context.Response);
//}
if (HttpContext.Current.Session["User_ID"] != null)
{
WriteFile(bytes, fileName, MimeType + " " + extension_Without_dot, context.Response);
}
}
/// <summary>
/// Sends a byte array to the client
/// </summary>
/// <param name="content">binary file content</param>
/// <param name="fileName">the filename to be sent to the client</param>
/// <param name="contentType">the file content type</param>
private void WriteFile(byte[] content, string fileName, string contentType, HttpResponse response)
{
response.Buffer = true;
response.Clear();
response.ContentType = contentType;
response.AddHeader("content-disposition", "attachment; filename=" + fileName);
response.BinaryWrite(content);
response.Flush();
response.End();
}
private string GetMimeType(string fileName)
{
string mimeType = "application/unknown";
string ext = System.IO.Path.GetExtension(fileName).ToLower();
Microsoft.Win32.RegistryKey regKey = Microsoft.Win32.Registry.ClassesRoot.OpenSubKey(ext);
if (regKey != null && regKey.GetValue("Content Type") != null)
mimeType = regKey.GetValue("Content Type").ToString();
return mimeType;
}
public bool IsReusable
{
get
{
return false;
}
}
#endregion
}
}
在if (HttpContext.Current.Session["User_ID"] != null)
的行中,当会话变量为空时,我得到以下异常:
'/'应用程序服务器错误。
对象引用未设置为对象的实例。描述:一个执行当前web时发生未处理的异常请求。有关的详细信息,请查看堆栈跟踪错误和它在代码中的起源。
Exception Details: System。NullReferenceException:对象引用不存在设置为对象的实例
我该如何解决这个问题?
由于通用处理程序被设计为准系统请求处理程序,因此它们默认不支持Session。您需要做的是用IRequiresSessionState
接口修饰处理程序类:
public class Handler : IHttpHandler, IRequiresSessionState
这会导致ASP。. NET运行时为请求初始化会话容器。然后,您可以使用HttpContext
中的Session
实例。
http://msdn.microsoft.com/en-us/library/system.web.sessionstate.irequiressessionstate.aspx