拦截asp.net输出流并进行处理的方法

本文实例主要实现对已经生成了HTML的页面做一些输出到客户端之前的处理。

方法的实现原理是：把Response的输出重定向到自定义的容器内，也就是我们的StringBuilder对象里，在HTML所有的向页面输出都变成了向StringBuilder输出，然后我们对StringBuilder处理完成之后，再把Response的输出重定向到原来的页面上，然后再通过Response.Write方法把StringBuilder的内容输出到页面上。

这里之所以用反射，是因为Response对象的OutPut属性是只读的，通过反编译该类的程序集发现，OutPut实际上是内部私有成员 _writer来实现输出的。因此通过反射来改写该成员的值以实现输出流的重定向。

具体功能代码如下：

using System; using System.Collections.Generic; using System.Linq; using System.Web; using System.Web.UI; using System.Web.UI.WebControls; using System.Text; using System.IO; using System.Reflection; public partial class _Default : System.Web.UI.Page  {   StringBuilder content = new StringBuilder();   TextWriter tw_old, tw_new;   FieldInfo tw_field;   protected void Page_Load(object sender, EventArgs e)   {     var context = HttpContext.Current;      tw_old = context.Response.Output;//Response原来的OutPut     tw_new = new StringWriter(content);//一个StringWriter,用来获取页面内容     var type_rp = context.Response.GetType();     //通过反射获取对象的私有字段     tw_field = type_rp.GetField("_writer", System.Reflection.BindingFlags.Public | System.Reflection.BindingFlags.NonPublic | System.Reflection.BindingFlags.Instance);     tw_field.SetValue(context.Response, tw_new);   }   protected override void Render(HtmlTextWriter writer)   {     base.Render(writer);     //替换回Response的OutPut     tw_field.SetValue(HttpContext.Current.Response, tw_old);     //做自己的处理     content.AppendLine("<!--江湖小子-->");     HttpContext.Current.Response.Write(content.ToString());   } }  

方法二，用HttpModul来实现：  

using System; using System.Collections.Generic; using System.Linq; using System.Web; using System.Web.UI; using System.IO; using System.Text; using System.Reflection; /// <summary> ///HttpModule 的摘要说明 /// </summary> public class HttpModule : IHttpModule {   private HttpApplication _contextApplication;   private TextWriter tw_new, tw_old;   private StringBuilder _content;   private FieldInfo tw_field;   public void Init(HttpApplication context)   {     _contextApplication = context;     _contextApplication.PreRequestHandlerExecute += new EventHandler(_contextApplication_PreRequestHandlerExecute);   }   public void Dispose()   {     _contextApplication = null;     _contextApplication.Dispose();   }   public void _contextApplication_PreRequestHandlerExecute(object sender, EventArgs e)   {     HttpContext context = _contextApplication.Context;      var _page = context.Handler as System.Web.UI.Page;     _page.Unload += new EventHandler(_page_Unload);      _content = new StringBuilder();     tw_old = context.Response.Output;//Response原来的OutPut     tw_new = new StringWriter(_content);//一个StringWriter,用来获取页面内容     var type_rp = context.Response.GetType();     tw_field = type_rp.GetField("_writer", System.Reflection.BindingFlags.Public | System.Reflection.BindingFlags.NonPublic | System.Reflection.BindingFlags.Instance);     tw_field.SetValue(context.Response, tw_new);   }   void _page_Unload(object sender, EventArgs e)   {     //替换回Response的OutPut     tw_field.SetValue(HttpContext.Current.Response, tw_old);     //做自己的处理     _content.AppendLine("<!--江湖小子-->");     HttpContext.Current.Response.Write(_content.ToString());   } }