javaweb开发（九）：Listener监听器

应用上下文全局监听器

 # web.xml
    <context-param>
        <param-name>url</param-name>
        <param-value>https://xdclass.net</param-value>
    </context-param>
 
    <context-param>
        <param-name>topic</param-name>
        <param-value>java课堂</param-value>
    </context-param>
 
# 实体类
public class Config {
 
    private String url;
 
    private String topic;
 
    public String getUrl() {
        return url;
    }
 
    public void setUrl(String url) {
        this.url = url;
    }
 
    public String getTopic() {
        return topic;
    }
 
    public void setTopic(String topic) {
        this.topic = topic;
    }
 
}
 
# 监听器
@WebListener
public class ContextListener implements ServletContextListener {
 
    /**
     * 初始化
     * @param sce
     */
    @Override
    public void contextInitialized(ServletContextEvent sce) {
        System.out.println("ContextListener contextInitialized");
        // 从领域对象中获取数据
        ServletContext servletContext = sce.getServletContext();
        String url = servletContext.getInitParameter("url");
        String topic = servletContext.getInitParameter("topic");
        // 将数据设置到config对象中
        Config config = new Config();
        config.setTopic(topic);
        config.setUrl(url);
        // 将config对象设置到领域对象中
        servletContext.setAttribute("config",config);
    }
 
    /**
     * 销毁
     * @param sce
     */
    @Override
    public void contextDestroyed(ServletContextEvent sce) {
        System.out.println("ContextListener contextDestroyed");
    }
 
}
 
# 编写用于测试的servlet，获取领域对象中的数据
@WebServlet("/forward")
public class DispatchServlet extends HttpServlet {
 
    @Override
    protected void doGet(HttpServletRequest req, HttpServletResponse response) throws ServletException, IOException {
        // 测试是否从web.xml 中获取到值
        Config config = (Config) req.getServletContext().getAttribute("config");
        System.out.println(config.getTopic());
        // 请求转发
        System.out.println("DispatchServlet doGet");
        req.getRequestDispatcher("/index.jsp").forward(req,response);
    }
 
}

测试

 http://localhost:8081/forward
 
# 控制台打印如下，说明监听器从web.xml中获取到了数据
java����
DispatchServlet doGet

SessionListener统计在线人数

 # ContextListener中设置初始值
servletContext.setAttribute("onlineNum",0);
 
# 编写SessionListener 
@WebListener
public class SessionListener implements HttpSessionListener {
 
    /**
     * 初始化
     * @param se
     */
    @Override
    public void sessionCreated(HttpSessionEvent se) {
        System.out.println("SessionListener sessionCreated");
        ServletContext servletContext  = se.getSession().getServletContext();
        //获取在线人数
        Integer onlineNum = (Integer)servletContext.getAttribute("onlineNum");
        //新增1
        servletContext.setAttribute("onlineNum",++onlineNum);
    }
 
    /**
     * 销毁
     * @param se
     */
    @Override
    public void sessionDestroyed(HttpSessionEvent se) {
        System.out.println("SessionListener sessionDestroyed");
        ServletContext servletContext  = se.getSession().getServletContext();
        //获取在线人数
        Integer onlineNum = (Integer)servletContext.getAttribute("onlineNum");
        //减少1
        servletContext.setAttribute("onlineNum",--onlineNum);
    }
 
}
 
# 编写add.jsp
<%@ page contentType="text/html;charset=UTF-8" language="java" %>
<html>
<head>
    <title>javaweb统计在线人数</title>
</head>
<body>
 
近30分钟在线人数: ${applicationScope.onlineNum}
 
</body>
</html>

取消勾选
启动测试
使用RequestListener统计访问量

 # ContextListener中设置初始访问值
servletContext.setAttribute("totalVisit",0);
 
# 编写RequestListener 
@WebListener
public class RequestListener implements ServletRequestListener {
 
    /**
     * 销毁的方法
     * @param sre
     */
    @Override
    public void requestDestroyed(ServletRequestEvent sre) {
        System.out.println(" RequestListener requestDestroyed");
    }
 
    /**
     * 初始化
     * @param sre
     */
    @Override
    public void requestInitialized(ServletRequestEvent sre) {
        System.out.println(" RequestListener requestInitialized");
        Integer totalVisit = (Integer)sre.getServletContext().getAttribute("totalVisit");
        System.out.println("历史总访问次数："+totalVisit);
        totalVisit++;
        sre.getServletContext().setAttribute("totalVisit",totalVisit);
    }
    
}
 
# jsp中获取访问量
应用服务器启动后总访问次数：${totalVisit}

测试

posted @ 2022-04-14 13:45 DogLeftover 阅读(17) 评论(0) 编辑收藏举报

刷新页面返回顶部

登录后才能查看或发表评论，立即登录或者逛逛博客园首页

相关博文：

· javaweb开发（四）：servlet应用上下文与jsp

· javaweb开发（八）：sevlet之filter过滤器

· javaweb：监听器

· 监听器Listener

· JavaWeb基础学习笔记16——Listener（监听器）

阅读排行：
· 阿里巴巴 QwQ-32B真的超越了 DeepSeek R-1吗？
· 10年+ .NET Coder 心语 ── 封装的思维：从隐藏、稳定开始理解其本质意义
· 【设计模式】告别冗长if-else语句：使用策略模式优化代码结构
· 字符编码：从基础到乱码解决
· 提示词工程——AI应用必不可少的技术

javaweb开发（九）：Listener监听器

我的标签

合集 (4)

随笔分类 (1350)

阅读排行榜

推荐排行榜

	# web.xml
	<context-param>
	<param-name>url</param-name>
	<param-value>https://xdclass.net</param-value>
	</context-param>

	<context-param>
	<param-name>topic</param-name>
	<param-value>java课堂</param-value>
	</context-param>

	# 实体类
	public class Config {

	private String url;

	private String topic;

	public String getUrl() {
	return url;
	}

	public void setUrl(String url) {
	this.url = url;
	}

	public String getTopic() {
	return topic;
	}

	public void setTopic(String topic) {
	this.topic = topic;
	}

	}

	# 监听器
	@WebListener
	public class ContextListener implements ServletContextListener {

	/**
	* 初始化
	* @param sce
	*/
	@Override
	public void contextInitialized(ServletContextEvent sce) {
	System.out.println("ContextListener contextInitialized");
	// 从领域对象中获取数据
	ServletContext servletContext = sce.getServletContext();
	String url = servletContext.getInitParameter("url");
	String topic = servletContext.getInitParameter("topic");
	// 将数据设置到config对象中
	Config config = new Config();
	config.setTopic(topic);
	config.setUrl(url);
	// 将config对象设置到领域对象中
	servletContext.setAttribute("config",config);
	}

	/**
	* 销毁
	* @param sce
	*/
	@Override
	public void contextDestroyed(ServletContextEvent sce) {
	System.out.println("ContextListener contextDestroyed");
	}

	}

	# 编写用于测试的servlet，获取领域对象中的数据
	@WebServlet("/forward")
	public class DispatchServlet extends HttpServlet {

	@Override
	protected void doGet(HttpServletRequest req, HttpServletResponse response) throws ServletException, IOException {
	// 测试是否从web.xml 中获取到值
	Config config = (Config) req.getServletContext().getAttribute("config");
	System.out.println(config.getTopic());
	// 请求转发
	System.out.println("DispatchServlet doGet");
	req.getRequestDispatcher("/index.jsp").forward(req,response);
	}

	}

	http://localhost:8081/forward

	# 控制台打印如下，说明监听器从web.xml中获取到了数据
	java��
	DispatchServlet doGet

	# ContextListener中设置初始值
	servletContext.setAttribute("onlineNum",0);

	# 编写SessionListener
	@WebListener
	public class SessionListener implements HttpSessionListener {

	/**
	* 初始化
	* @param se
	*/
	@Override
	public void sessionCreated(HttpSessionEvent se) {
	System.out.println("SessionListener sessionCreated");
	ServletContext servletContext = se.getSession().getServletContext();
	//获取在线人数
	Integer onlineNum = (Integer)servletContext.getAttribute("onlineNum");
	//新增1
	servletContext.setAttribute("onlineNum",++onlineNum);
	}

	/**
	* 销毁
	* @param se
	*/
	@Override
	public void sessionDestroyed(HttpSessionEvent se) {
	System.out.println("SessionListener sessionDestroyed");
	ServletContext servletContext = se.getSession().getServletContext();
	//获取在线人数
	Integer onlineNum = (Integer)servletContext.getAttribute("onlineNum");
	//减少1
	servletContext.setAttribute("onlineNum",--onlineNum);
	}

	}

	# 编写add.jsp
	<%@ page contentType="text/html;charset=UTF-8" language="java" %>
	<html>
	<head>
	<title>javaweb统计在线人数</title>
	</head>
	<body>

	近30分钟在线人数: ${applicationScope.onlineNum}

	</body>
	</html>

	# ContextListener中设置初始访问值
	servletContext.setAttribute("totalVisit",0);

	# 编写RequestListener
	@WebListener
	public class RequestListener implements ServletRequestListener {

	/**
	* 销毁的方法
	* @param sre
	*/
	@Override
	public void requestDestroyed(ServletRequestEvent sre) {
	System.out.println(" RequestListener requestDestroyed");
	}

	/**
	* 初始化
	* @param sre
	*/
	@Override
	public void requestInitialized(ServletRequestEvent sre) {
	System.out.println(" RequestListener requestInitialized");
	Integer totalVisit = (Integer)sre.getServletContext().getAttribute("totalVisit");
	System.out.println("历史总访问次数："+totalVisit);
	totalVisit++;
	sre.getServletContext().setAttribute("totalVisit",totalVisit);
	}

	}

	# jsp中获取访问量
	应用服务器启动后总访问次数：${totalVisit}