拦截asp.net输出流做处理

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。

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();  
    }  
}

mayb