拦截asp.net输出流做处理

本文标题是指对已经生成了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();
    }
}

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