using System;

using System.Collections.Generic;

using System.Collections.Specialized;

using System.Linq;

using System.Reflection;

using System.Web;

namespace WebApplication4

{

    public class FilterForbiddenWordModule:IHttpModule

    {

        void IHttpModule.Dispose() { }

        void IHttpModule.Init(HttpApplication context)

        {

            context.BeginRequest += new EventHandler(OnBeginRequest);

        }

        private static void OnBeginRequest(object sender, EventArgs e)

        {

            var request = (sender as HttpApplication).Request;

            ProcessCollection(request.QueryString);

            ProcessCollection(request.Form);

        }

        private static void ProcessCollection(NameValueCollection collection)

        {

            var copy = new NameValueCollection();

         //   copy.GetType().GetProperty("IsReadOnly").SetValue(copy, false);

            foreach (string key in collection.AllKeys)

            {

                Array.ForEach(

                    collection.GetValues(key),

                    v => copy.Add(key, ForbiddenWord.Filter(v)));

            }

            typeof(NameObjectCollectionBase).GetProperty("IsReadOnly",BindingFlags.Instance | BindingFlags.NonPublic).SetValue(collection, false);

            collection.Clear();

            collection.Add(copy);

        }

    }

    public static class ForbiddenWord

    {

        public static string Filter(string original)

        {

            return original.Replace("关键词", "替换后");

        }

    }

}