本文为JavaWeb基础Servlet监听器相关知识介绍~, Java全栈学习路线可参考:【Java全栈学习路线】最全的Java学习路线及知识清单,Java自学方向指引,内含最全Java全栈学习技术清单~
(1)定义一个监听器实现 ApplicationListener 接口,重写 onApplicationEvent 方法,获取 applicationContext 上下文中的 Bean 对象,执行相应方法后将结果放到 ServletContext 的作用域对象 application 中。
@Component
public class ServletContextListener implements ApplicationListener<ContextRefreshedEvent> {
@Override
public void onApplicationEvent(ContextRefreshedEvent event) {
if (event.getApplicationContext().getParent() == null) {
ApplicationContext applicationContext = event.getApplicationContext();
UserService userService = applicationContext.getBean(UserService.class);
User user = userService.getUser();
ServletContext application = applicationContext.getBean(ServletContext.class);
application.setAttribute("user", user);
}
}
}
(2)定义测试接口
@RestController
@Slf4j
public class UserController {
@GetMapping("/api/getUser")
public User getUser(HttpServletRequest request) {
ServletContext servletContext = request.getServletContext();
User user = (User) servletContext.getAttribute("user");
log.info("user: {}", user);
return user;
}
}
(3)查看测试结果
2021-12-28 10:55:56.472 INFO 10820 --- [nio-8080-exec-1] com.xpy.controller.UserController : user: User(id=1, nickname=PlanMak1r, password=123456)
(1)定义一个监听器实现 HttpSessionListener 接口,重写两个方法,获取 session 会话对象,并将数据放到 HttpSession 的作用域对象 session 中
@Component
@Slf4j
public class LoginSessionListener implements HttpSessionListener {
public static Integer count = 0;
@Override
public void sessionCreated(HttpSessionEvent se) {
log.info("新用户上线...");
count++;
se.getSession().getServletContext().setAttribute("personCount", count);
}
@Override
public void sessionDestroyed(HttpSessionEvent se) {
log.info("用户下线了...");
count--;
se.getSession().getServletContext().setAttribute("personCount", count);
}
}
(2)定义测试接口
@RestController
@Slf4j
public class LoginController {
@GetMapping("/getOnlineUser")
public String getOnlineUser(HttpServletRequest request) {
Integer personCount = (Integer) request.getServletContext().getAttribute("personCount");
log.info("登录的人数是: {}", (personCount == null ? 0 : personCount));
return "登录的人数是:" + (personCount == null ? 0 : personCount);
}
@GetMapping("logined")
public String logined(HttpSession session) {
session.setAttribute("user", new User(1L, "PlanMak1r", "123456"));
log.info("登录成功...");
return "success";
}
@GetMapping("logout")
public String logout(HttpSession session) {
session.invalidate();
log.info("退出成功...");
return "success";
}
}
(3)查看测试结果
2021-12-28 11:28:23.420 INFO 8232 --- [nio-8080-exec-1] com.xpy.controller.LoginController : 登录的人数是: 0
2021-12-28 11:28:29.436 INFO 8232 --- [nio-8080-exec-2] c.x.c.listener.LoginSessionListener : 新用户上线...
2021-12-28 11:28:29.450 INFO 8232 --- [nio-8080-exec-2] com.xpy.controller.LoginController : 登录成功...
2021-12-28 11:28:39.832 INFO 8232 --- [nio-8080-exec-3] com.xpy.controller.LoginController : 登录的人数是: 1
2021-12-28 11:28:49.381 INFO 8232 --- [nio-8080-exec-5] c.x.c.listener.LoginSessionListener : 用户下线了...
2021-12-28 11:28:49.381 INFO 8232 --- [nio-8080-exec-5] com.xpy.controller.LoginController : 退出成功...
2021-12-28 11:28:51.167 INFO 8232 --- [nio-8080-exec-6] com.xpy.controller.LoginController : 登录的人数是: 0
(4)导入 freemarker 依赖
<dependency>
<groupId>org.springframework.bootgroupId>
<artifactId>spring-boot-starter-freemarkerartifactId>
dependency>
(5)配置 freemarker
spring:
freemarker:
suffix: .html
cache: false
(6)定义页面跳转
@Controller
public class IndexController {
@GetMapping("/index")
public String index() {
return "index";
}
}
(7)定义展示页面实现实时展示
<!DOCTYPE html>
<html lang="en">
<head>
<meta charset="UTF-8">
<title>首页</title>
</head>
<body>
<h1><span id="personCount"></span></h1>
<script src="/js/jquery.min.js"></script>
<script>
$(function () {
function loadOnlineUserCount() {
$.get("/getOnlineUser", function (res) {
$("#personCount").html(res);
});
}
loadOnlineUserCount();
setInterval(loadOnlineUserCount, 3000);
})
</script>
</body>
</html>
对request对象实际上就是对ServletRequest进行监听,主要的监听接口有两个:
实现ServletRequestListener接口,对浏览器的请求的创建和销毁进行监听,复写的方法有两个:
实现ServletRequestAttributeListener接口,对request域对象范围属性的设置、移除和修改进行监听,复写的方法有三个:
package com.wanbangee.listener;
import javax.servlet.ServletRequestAttributeEvent;
import javax.servlet.ServletRequestAttributeListener;
import javax.servlet.ServletRequestEvent;
import javax.servlet.ServletRequestListener;
import javax.servlet.annotation.WebListener;
@WebListener
public class ServletRequestListenerDemo implements ServletRequestListener, ServletRequestAttributeListener {
public void requestInitialized(ServletRequestEvent sre) {
System.out.println("请求的创建");
}
public void requestDestroyed(ServletRequestEvent sre) {
System.out.println("请求的销毁");
}
public void attributeAdded(ServletRequestAttributeEvent srae) {
System.out.println("将信息添加到request域对象时执行");
}
public void attributeRemoved(ServletRequestAttributeEvent srae) {
System.out.println("从request域对象中移除信息时执行");
}
public void attributeReplaced(ServletRequestAttributeEvent srae) {
System.out.println("修改request域对象中的信息时执行");
}
}
总结:
Java全栈学习路线可参考:【Java全栈学习路线】最全的Java学习路线及知识清单,Java自学方向指引,内含最全Java全栈学习技术清单~