Listener

ServletContextListener:监听web的启动和关闭。

package com.li.test;

import java.sql.Connection;
import java.sql.DriverManager;
import java.sql.SQLException;

import javax.servlet.ServletContext;
import javax.servlet.ServletContextEvent;
import javax.servlet.ServletContextListener;
import javax.servlet.annotation.WebListener;

/**
 * Application Lifecycle Listener implementation class ListerTest_1
 * 
 */
@WebListener
public class ListerTest_1 implements ServletContextListener {

    /**
     * Default constructor.
     */
    public ListerTest_1() {}

    /**
     * @see ServletContextListener#contextInitialized(ServletContextEvent)
     */
    public void contextInitialized(ServletContextEvent event) {

        ServletContext context = event.getServletContext();

        String driver = context.getInitParameter("driver");
        String username = context.getInitParameter("username");
        String password = context.getInitParameter("password");
        String url = context.getInitParameter("url");

        try {

            Class.forName(driver);
            Connection conn = DriverManager.getConnection(url, username, password);
            context.setAttribute("conn", conn);

        } catch (Exception e) {
            System.out.println("connect error: " + e.getMessage());
            e.printStackTrace();
        }

    }

    /**
     * @see ServletContextListener#contextDestroyed(ServletContextEvent)
     */
    public void contextDestroyed(ServletContextEvent event) {

        ServletContext context = event.getServletContext();
        Connection conn = (Connection) context.getAttribute("conn");

        if (conn != null) {
            try {
                conn.close();
            } catch (SQLException e) {
                e.printStackTrace();
            }
        }
    }

}

ServletContextAttributeListener：监听application范围内的属性的变化。

package com.li.test;

import javax.servlet.ServletContext;
import javax.servlet.ServletContextAttributeEvent;
import javax.servlet.ServletContextAttributeListener;
import javax.servlet.annotation.WebListener;

/**
 * Application Lifecycle Listener implementation class ListerTest_2
 * 
 */
@WebListener
public class ListerTest_2 implements ServletContextAttributeListener {

    /**
     * Default constructor.
     */
    public ListerTest_2() {}

    /**
     * @see ServletContextAttributeListener#attributeAdded(ServletContextAttributeEvent)
     */
    public void attributeAdded(ServletContextAttributeEvent event) {
        
        ServletContext application = event.getServletContext();
        
        String name = event.getName();
        Object value = event.getValue();
        
        System.out.println(application+"范围内添加了属性:"+name+",值为："+value);
    }

    /**
     * @see ServletContextAttributeListener#attributeReplaced(ServletContextAttributeEvent)
     */
    public void attributeReplaced(ServletContextAttributeEvent event) {
        
ServletContext application = event.getServletContext();
        
        String name = event.getName();
        Object value = event.getValue();
        
        System.out.println(application+"范围内删除了属性:"+name+",值为："+value);
    }

    /**
     * @see ServletContextAttributeListener#attributeRemoved(ServletContextAttributeEvent)
     */
    public void attributeRemoved(ServletContextAttributeEvent event) {
        
ServletContext application = event.getServletContext();
        
        String name = event.getName();
        Object value = event.getValue();
        
        System.out.println(application+"范围内修改了属性:"+name+",值为："+value);
    }

}

HttpSessionListener：监听session的开始和结束。

HttpSessionAttributeListener

HttpSessionActivationListener

HttpSessionBindingListener

package com.li.test;

import java.util.HashMap;
import java.util.Map;

import javax.servlet.ServletContext;
import javax.servlet.annotation.WebListener;
import javax.servlet.http.HttpSession;
import javax.servlet.http.HttpSessionAttributeListener;
import javax.servlet.http.HttpSessionBindingEvent;
import javax.servlet.http.HttpSessionEvent;
import javax.servlet.http.HttpSessionListener;

/**
 * Application Lifecycle Listener implementation class ListerTest_4
 * 
 */
@WebListener
public class ListerTest_4 implements HttpSessionListener, HttpSessionAttributeListener {

    /**
     * Default constructor.
     */
    public ListerTest_4() {}

    /**
     * @see HttpSessionAttributeListener#attributeRemoved(HttpSessionBindingEvent)
     */
    public void attributeRemoved(HttpSessionBindingEvent arg0) {}

    /**
     * @see HttpSessionAttributeListener#attributeAdded(HttpSessionBindingEvent)
     */
    public void attributeAdded(HttpSessionBindingEvent arg0) {}

    /**
     * @see HttpSessionAttributeListener#attributeReplaced(HttpSessionBindingEvent)
     */
    public void attributeReplaced(HttpSessionBindingEvent arg0) {}

    /**
     * @see HttpSessionListener#sessionCreated(HttpSessionEvent)
     */
    public void sessionCreated(HttpSessionEvent sv) {

        HttpSession session = sv.getSession();
        ServletContext application = session.getServletContext();
        String sessionId = session.getId();

        if (session.isNew()) {

            String user = (String) session.getAttribute("user");
            user = (user == null) ? "游客" : user;

            Map<String, String> online = (Map<String, String>) application.getAttribute("online");
            if (online == null) {
                online = new HashMap<String, String>();
                online.put(sessionId, user);
            }
            application.setAttribute("online", online);
        }
    }

    /**
     * @see HttpSessionListener#sessionDestroyed(HttpSessionEvent)
     */
    public void sessionDestroyed(HttpSessionEvent sv) {

        HttpSession session = sv.getSession();
        ServletContext application = session.getServletContext();
        String sessionId = session.getId();
        Map<String, String> online = (Map<String, String>) application.getAttribute("online");

        if (online != null) {
            online.remove(sessionId);
        }
        application.setAttribute("online", online);
    }

}

ServletRequestListener

package com.li.test;

import javax.servlet.ServletRequestEvent;
import javax.servlet.ServletRequestListener;
import javax.servlet.annotation.WebListener;
import javax.servlet.http.HttpServletRequest;

/**
 * Application Lifecycle Listener implementation class ListerTest_3
 * 
 */
@WebListener
public class ListerTest_3 implements ServletRequestListener {

    /**
     * Default constructor.
     */
    public ListerTest_3() {}

    /**
     * @see ServletRequestListener#requestDestroyed(ServletRequestEvent)
     */
    public void requestDestroyed(ServletRequestEvent event) {

        HttpServletRequest request = (HttpServletRequest) event.getServletRequest();
        System.out.println(request);
    }

    /**
     * @see ServletRequestListener#requestInitialized(ServletRequestEvent)
     */
    public void requestInitialized(ServletRequestEvent event) {

        HttpServletRequest request = (HttpServletRequest) event.getServletRequest();
        System.out.println(request);
    }

}

ServletRequestAttributeListener