404页面

  <system.web>
    <customErrors mode="On" defaultRedirect="error.asp" redirectMode="ResponseRewrite">
      <error statusCode="404" redirect="404.aspx" />
    </customErrors>  
  </system.web>
  <system.webServer>
    <httpErrors errorMode="Custom">
      <!--有3中 Custom, DetailedLocalOnly, Detailed-->
      <remove statusCode="404" />
      <error statusCode="404" path="/404.aspx" responseMode="ExecuteURL"  />
    </httpErrors>
  </system.webServer>

    protected void Page_Load(object sender, EventArgs e)
    {
        Response.StatusCode = 404;
    }

    try
    {
        throw new HttpException(404, "PageNotFound"); //可以 throw to 404page
    }
    catch (Exception ex) 
    {
        throw ex;
    }