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());
  }
}
 

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。