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()); 
 } 
} 
 

方法三：

public class HttpModule : IHttpModule 
{ 
 private HttpApplication _contextApplication; 
 private TextWriter tw_new, tw_old; 
 private StringBuilder _content; 
 private FieldInfo tw_field; 
 public void Init(HttpApplication application) 
 { 
 _contextApplication = application; 
 _contextApplication.BeginRequest += new EventHandler(_contextApplication_BeginRequest); 
 _contextApplication.EndRequest +=new EventHandler(_contextApplication_EndRequest); 
 } 
 void _contextApplication_BeginRequest(object sender, EventArgs e) 
 { 
 _content = new StringBuilder(); 
 tw_old = _contextApplication.Response.Output; 
 tw_new = new StringWriter(_content); 
 var type_rp = _contextApplication.Response.GetType(); 
 tw_field = type_rp.GetField("_writer", System.Reflection.BindingFlags.Public | System.Reflection.BindingFlags.NonPublic | System.Reflection.BindingFlags.Instance); 
 tw_field.SetValue(_contextApplication.Response, tw_new); 
 } 
 void _contextApplication_EndRequest(object sender, EventArgs e) 
 { 
 tw_field.SetValue(_contextApplication.Response, tw_old); 
 //做自己的处理 
 _content.AppendLine("<!--jhxz-->"); 
 _contextApplication.Response.Write(_content.ToString()); 
 } 
 public void Dispose() 
 { 
 _contextApplication = null; 
 _contextApplication.Dispose(); 
 } 
}

相信本文所述对大家的asp.net程序设计有一定的借鉴价值。