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。