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