JAVA监听器Listener
一、 简介
监听器用于对web中内置对象的状态或者属性变化进行监听并做出相应响应的一种Servlet;在内置对象的生命周期中,产生、销毁等状态发生变化时,监听器就会进行监听并做出响应,当内置对象的属性发生增加,删除,修改等变化时,监听器也会做出相应响应。
二、 分类
ServletContext对象监听器
HttpSession对象监听器
ServletRequest对象监听器
三、 如何配置监听器
在web.xml中添加:
<listener>
<listener-class>com.zsl33.mvc.listener.RequestListener</listener-class>
<listener-class>com.zsl33.mvc.listener.SessionListener</listener-class>
<listener-class>com.zsl33.mvc.listener.ApplicationListener</listener-class>
</listener>
使用注解进行配置:
在监听器类上加上
@WebListener
四、 接口
Session监听器类对Session状态进行监听需要实现javax.servlet.http.HttpSessionListener
接口,对Session属性进行监听则需要实现``` javax.servlet.http.HttpSessionAttributeListener
接口
实例:
@WebListener
public class SessionListener implements HttpSessionListener,HttpSessionAttributeListener{
@Override
public void attributeAdded(HttpSessionBindingEvent arg0) {
// TODO Auto-generated method stub
System.out.println("session增加:"+arg0.getSession().getId());
}
@Override
public void attributeRemoved(HttpSessionBindingEvent arg0) {
// TODO Auto-generated method stub
System.out.println("session删除:"+arg0.getSession().getId());
}
@Override
public void attributeReplaced(HttpSessionBindingEvent arg0) {
// TODO Auto-generated method stub
System.out.println("session替换:"+arg0.getSession().getId());
}
@Override
public void sessionCreated(HttpSessionEvent arg0) {
// TODO Auto-generated method stub
System.out.println("session创建:"+arg0.getSession().getId());
}
@Override
public void sessionDestroyed(HttpSessionEvent arg0) {
// TODO Auto-generated method stub
System.out.println("session销毁:"+arg0.getSession().getId());
}
}
Request监听器类对Request状态进行监听需要实现javax.servlet.ServletRequestListener
接口,对Request属性进行监听需要实现javax.servlet.ServletRequestAttributeListener
接口
实例:
@WebListener
public class RequestListener implements ServletRequestListener,ServletRequestAttributeListener{
@Override
public void requestDestroyed(ServletRequestEvent arg0) {
// TODO Auto-generated method stub
System.out.println("监听:Request内置对象销毁");
}
@Override
public void requestInitialized(ServletRequestEvent arg0) {
// TODO Auto-generated method stub
System.out.println("监听:Request内置对象初始化");
}
@Override
public void attributeAdded(ServletRequestAttributeEvent arg0) {
// TODO Auto-generated method stub
System.out.println("监听:新增:"+arg0.getName()+":"+arg0.getValue());
}
@Override
public void attributeRemoved(ServletRequestAttributeEvent arg0) {
// TODO Auto-generated method stub
System.out.println("监听:删除:"+arg0.getName()+":"+arg0.getValue());
}
@Override
public void attributeReplaced(ServletRequestAttributeEvent arg0) {
// TODO Auto-generated method stub
System.out.println("监听:替换:"+arg0.getName()+":"+arg0.getValue());
}
}
Application监听器类对Application对象状态进行监听,需要实现javax.servlet.ServletContextListener
接口,对Application对象属性进行监听需要实现javax.servlet.ServletContextAttributeListener
接口;
实例:
@WebListener
public class ApplicationListener implements ServletContextListener,ServletContextAttributeListener{
@Override
public void contextDestroyed(ServletContextEvent arg0) {
System.out.println("监听:Application内置对象销毁");
}
@Override
public void contextInitialized(ServletContextEvent arg0) {
System.out.println("监听:Application内置对象初始化");
}
@Override
public void attributeAdded(ServletContextAttributeEvent arg0) {
System.out.println("监听:新增:"+arg0.getName()+":"+arg0.getValue());
}
@Override
public void attributeRemoved(ServletContextAttributeEvent arg0) {
System.out.println("监听:删除:"+arg0.getName()+":"+arg0.getValue());
}
@Override
public void attributeReplaced(ServletContextAttributeEvent arg0) {
System.out.println("监听:替换:"+arg0.getName()+":"+arg0.getValue());
}
}