过滤器和监听器

过滤器可以截取和修改进入一个servlet或者是jsp页面的请求

配置：

   Set Character Encoding

   com.util.setCharacterEncodingFilter

  

     encoding

     utf-8

  

  

     ignore

     true

  

类：

package com.util;

import javax.servlet.*;

import java.io.IOException;

public class SetCharacterEncodingFilter implements Filter{

  protected String encoding=null;

  protected FilterConfig filterConfig=null;

  protected boolean ignore=true;

  public void init(FilterConfig filterConfig)throws ServletException{

     this.filterConfig=filterConfig;

     this.encoding=filterConfig.getInitParameter("encoding");

     String value=filterConfig.getInitParameter("ignore");

     if(value==null)

        this.ingore=true;

     else if(value.equalsIgnoreCase("true"))

        this.ignore=true;

     else if(value.equalsIgnoreCase("yes"))

        this.ignore=true;

     else

        this.ignore=false;

  }

public void doFilter(ServletRequest request,ServletResponse response,FilterChain chain)throws IOException,ServletException{

   if(ignore||(request.getCharacterEncoding())==null){

       String encoding=selectEncoding(request);

       if(encoding!=null)

            request.setCharacterEncoding(encoding);

   }

   chain.doFilter(request,response);  

}

protected String selectEncoding(ServletRequest request){

   return (this.encoding);

}

public void destory(){

  this.encoding=null;

  this.filterConfig=null;

}

}

映射：

   Set Character Encoding

   SomeServlet

    ///*

 

 

监听器：是建立或者修改servlet环境或会话对象时通知的类

配置：

   listeners.SessionListener

类：

package listener;

inport javax.servlet.http.*;

import javax.servlet.*;

public class SessionListener implements HttpSessionListener,ServletContextListener,ServletContextAttributeListener{

private static int count;

private ServletContect context=null;

public SessionListener(){

 count=0;

}

//创建一个session时激发

public void sessionCreate(HttpSessionEvent se){

count++;

setContext(se);

}

public void sessionDestroyed(HttpSessionEvent se){

 if(count>0)

    count--；

setContext(se);

}

//设置context的属性，它将激发attributeReplaced或attibuteAdded方法

public void setContext(HttpSessionEvent se){

 se.getSession().getServletContext().setAttribute("onLine",new Integer(count));

}

//增加一个新的属性时触发

public void attributeAdded(ServletContextAttributeEvent event){}

//替换一个属性时触发

public void attributeReplaced(ServletContextAttributeEvent event){}

//删除一个属性时触发

public void attributeRemoved(ServletContextAttributeEvent event){}

//context删除时触发

public void contextDestroyed(ServletContextAttributeEvent event){

this.context=null;

}

//context初始化时激发

public void contextInitialized(ServeltContextEvent event){

 this.event=event.getServletContext();

}

}