Listener 监听对象的属性变化

　　Listener用于监听Session、context、Request的属性变化，接口名称格式为xxxAttributeListener,包括HttpSessionAttributeListener、ServletContextAttributeLIstener、ServletRequesAttributeListener。当向被监听的对象中添加、更新、移除属性时，分别执行xxxAdded()、xxxReplaced()、xxxRemoved()方法。xxx分别代表Session、context、Request。

package linstener;

import javax.servlet.http.HttpSession;
import javax.servlet.http.HttpSessionAttributeListener;
import javax.servlet.http.HttpSessionBindingEvent;

import org.apache.commons.logging.Log;
import org.apache.commons.logging.LogFactory;

public class SessionAttributeListenerTest implements HttpSessionAttributeListener {
    
    Log log=LogFactory.getLog(this.getClass());
    @Override
    public void attributeAdded(HttpSessionBindingEvent arg0) {
        
        //添加属性时被调用
        HttpSession session=arg0.getSession();
        String name=arg0.getName();
        log.info("新建session 属性："+name+",值为："+arg0.getValue());
    }

    @Override
    public void attributeRemoved(HttpSessionBindingEvent arg0) {
        //删除属性前被调用
        HttpSession session =arg0.getSession();
        String name=arg0.getName();
        log.info("删除session属性："+name+",值为："+arg0.getValue());
    }

    @Override
    public void attributeReplaced(HttpSessionBindingEvent arg0) {
        //修改属性时被调用
        HttpSession session =arg0.getSession();
        String name=arg0.getName();
        Object oldValue=arg0.getValue();
        log.info("修改session属性："+name+", 原值："+oldValue+",新值："+session.getAttribute(name));
    }

}

 web.xml 配置

<listener>
      <listener-class>
          linstener.SessionAttributeListenerTest
      </listener-class>
 </listener>