Java过滤器与监听器间区别与联系

@Slf4j
public class WebmvcFilter implements Filter {
    @Override
    public void init(FilterConfig filterConfig) throws ServletException {
        String encoding = filterConfig.getInitParameter("encoding");
        log.info("-1-----encoding: {} ----->", encoding);
    }
    @Override
    public void doFilter(ServletRequest servletRequest, ServletResponse servletResponse, FilterChain filterChain) throws IOException, ServletException {
        log.info("0-----doFilter----->");
        filterChain.doFilter(servletRequest, servletResponse);
    }
    @Override
    public void destroy() {
        log.info("5-----destroy----->");
    }
}

@Configuration
public class WebFilterConfiguration {
    @Bean
    public FilterReGIStrationBean getWebMvcFilter(){
        FilterRegistrationBean<Filter> filterFilterRegistrationBean = new FilterRegistrationBean<>();
        WebMvcFilter webMvcFilter = new WebMvcFilter();
        filterFilterRegistrationBean.setFilter(webMvcFilter);
        filterFilterRegistrationBean.addUrlPatterns("/api/*");
        filterFilterRegistrationBean.setName("WebMvcFilter");
        filterFilterRegistrationBean.addInitParameter("encoding", "GBK");
        filterFilterRegistrationBean.setOrder(1);
        return filterFilterRegistrationBean;
    }
}

@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);
        }
    }
}

@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;
    }
}

@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);
    }
}

@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";
    }
}