攔截asp.net輸出流並進行處理的方法

本文實例主要實現對已經生成了HTML的頁面做一些輸出到客戶端之前的處理。

方法的實現原理是：把Response的輸出重定向到自定義的容器內，也就是我們的StringBuilder對象裡，在HTML所有的向頁面輸出都變成了向StringBuilder輸出，然後我們對StringBuilder處理完成之後，再把Response的輸出重定向到原來的頁面上，然後再通過Response.Write方法把StringBuilder的內容輸出到頁面上。

這裡之所以用反射，是因為Response對象的OutPut屬性是只讀的，通過反編譯該類的程序集發現，OutPut實際上是內部私有成員 _writer來實現輸出的。因此通過反射來改寫該成員的值以實現輸出流的重定向。

具體功能代碼如下：

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原來的OutPut 
    tw_new = new StringWriter(content);//一個StringWriter,用來獲取頁面內容 
    var type_rp = context.Response.GetType(); 
    //通過反射獲取對象的私有字段 
    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); 
    //替換回Response的OutPut 
    tw_field.SetValue(HttpContext.Current.Response, tw_old); 
    //做自己的處理 
    content.AppendLine("<!--江湖小子-->"); 
    HttpContext.Current.Response.Write(content.ToString()); 
  } 
} 
 

方法二，用HttpModul來實現：  

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 的摘要說明 
/// </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原來的OutPut 
    tw_new = new StringWriter(_content);//一個StringWriter,用來獲取頁面內容 
    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) 
  { 
    //替換回Response的OutPut 
    tw_field.SetValue(HttpContext.Current.Response, tw_old); 
    //做自己的處理 
    _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); 
    //做自己的處理 
    _content.AppendLine("<!--jhxz-->"); 
    _contextApplication.Response.Write(_content.ToString()); 
  } 
  public void Dispose() 
  { 
    _contextApplication = null; 
    _contextApplication.Dispose(); 
  } 
}

相信本文所述對大家的asp.net程序設計有一定的借鑒價值。