SpringBoot使用监听器

监听Servlet上下文对象

@Component
public class MyServletContextListener implements ApplicationListener {
    @Override
    public void onApplicationEvent(ContextRefreshedEvent contextRefreshedEvent) {
        // 先获取到application上下文
        ApplicationContext applicationContext = contextRefreshedEvent.getApplicationContext();
        // 获取对应service
        UserService userService = applicationContext.getBean(UserService.class);
        User user = userService.getUser();
        // 获取application域对象，将查到的信息放到application域中
        ServletContext servletContext = applicationContext.getBean(ServletContext.class);
        servletContext.setAttribute("user", user);
    }
}

监听HTTP会话Session对象

@Component
public class MyHttpSessionListener implements HttpSessionListener {
    private static final Logger logger = LoggerFactory.getLogger(MyHttpSessionListener.class);
    /**
     * 记录在线的用户数量
     */
    public Integer count = 0;
    @Override
    public synchronized void sessionCreated(HttpSessionEvent httpSessionEvent) {
        logger.info("新用户上线了");
        count++;
        httpSessionEvent.getSession().getServletContext().setAttribute("count", count);
    }
    @Override
    public synchronized void sessionDestroyed(HttpSessionEvent httpSessionEvent) {
        logger.info("用户下线了");
        count--;
        httpSessionEvent.getSession().getServletContext().setAttribute("count", count);
    }
}

监听客户端请求Servlet

@Component
public class MyServletRequestListener implements ServletRequestListener {
    private static final Logger logger = LoggerFactory.getLogger(MyServletRequestListener.class);

    @Override
    public void requestInitialized(ServletRequestEvent servletRequestEvent) {
        HttpServletRequest request = (HttpServletRequest) servletRequestEvent.getServletRequest();
        logger.info("session id为：{}", request.getRequestedSessionId());
        logger.info("request url为：{}", request.getRequestURL());

        request.setAttribute("name", "王博");
    }

    @Override
    public void requestDestroyed(ServletRequestEvent servletRequestEvent) {

        logger.info("request end");
        HttpServletRequest request = (HttpServletRequest) servletRequestEvent.getServletRequest();
        logger.info("request域中保存的name值为：{}", request.getAttribute("name"));
    }
}

自定义监听事件

# 自定义事件
public class MyEvent extends ApplicationEvent {
    private User user;
    public MyEvent(Object source, User user) {
        super(source);
        this.user = user;
    }
    // 省去get、set方法
}
# 自定义监听器
@Component
public class MyEventListener implements ApplicationListener {
    @Override
    public void onApplicationEvent(MyEvent myEvent) {
        // 把事件中的信息获取到
        User user = myEvent.getUser();
        // 处理事件，实际项目中可以通知别的微服务或者处理其他逻辑等等
        System.out.println("用户名：" + user.getUsername());
        System.out.println("密码：" + user.getPassword());
    }
}
# 发布事件监听器才能监听到
@Service
public class UserService {

    @Resource
    private ApplicationContext applicationContext;
    /**
     * 发布事件
     * @return
     */
    public User getUser2() {
        User user = new User(1L, "王博", "123456");
        // 发布事件
        MyEvent event = new MyEvent(this, user);
        applicationContext.publishEvent(event);
        return user;
    }
}