URL rewriting HttpModule (C#) : HTTP Modules « Development « ASP.NET Tutorial

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2. Development
3. HTTP Modules

using System.Web;

public class SimpleRewriter : System.Web.IHttpModule
{

    HttpApplication _application = null;

    public void Init(HttpApplication context)
    {
        context.BeginRequest += new System.EventHandler(context_BeginRequest);
        _application = context;
    }

    public void Dispose()
    {
    }

    private void context_BeginRequest(object sender, System.EventArgs e)
    {
        string requesturl =
            _application.Context.Request.Path.Substring(0,
                _application.Context.Request.Path.LastIndexOf("//")
            );

        string[] parameters = requesturl.Split(new char[] { '/' });

        if (parameters.Length > 1)
        {
            string firstname = parameters[1];
            string lastname = parameters[2];

            _application.Context.RewritePath("~/unfriendly.aspx?firstname=" +
                firstname + "&lastname=" + lastname);
        }
    }
}