public class LoginUserMap {
    private static Map<String, String> loginUserMap = new ConcurrentHashMap<String, String>();
    /**
     * set方法
     *
     * @param loginId   用戶唯一標識,用戶名或者用戶Id
     * @param sessionId sessionId
     */
    public static void setLoginUserMap(String loginId, String sessionId) {
        loginUserMap.put(loginId, sessionId);
    }
    /**
     * get方法
     *
     * @return
     */
    public static Map<String, String> getLoginUserMap() {
        return loginUserMap;
    }
    /**
     * 根據sessionId移除map中的值
     *
     * @param sessionId
     */
    public static void removeUser(String sessionId) {
        for (Map.Entry<String, String> entry : loginUserMap.entrySet()) {
            if (sessionId.equals(entry.getValue())) {
                loginUserMap.remove(entry.getKey());
                break;
            }
        }
    }
    /**
     * 判斷用戶是否在map中
     *
     * @param loginId
     * @param sessionId
     * @return
     */
    public static boolean isInLoginUsers(String loginId, String sessionId) {
        return (loginUserMap.containsKey(loginId) && sessionId.equals(loginUserMap.get(loginId)));
    }

@WebListener
public class SessionListener implements HttpSessionListener {
    private Logger logger=LoggerFactory.getLogger(SessionListener.class);
    @Override
    public void sessionCreated(HttpSessionEvent httpSessionEvent) {

    }
    @Override
    public void sessionDestroyed(HttpSessionEvent httpSessionEvent) {
        HttpSession session = httpSessionEvent.getSession();
        String sessionId = session.getId();
        //session銷毀時消除loginUserMap中的sessionId
        LoginUserMap.removeUser(sessionId);
        logger.info("session銷毀,sessionId:"+sessionId);
    }
}

 				//判斷是否重復登錄
                String loginName = username.getLoginName();//獲取用戶唯一標識
                //判斷當前用戶session是否改變
                if (!LoginUserMap.isInLoginUsers(loginName,session.getId())) {
                     //定義自己的實現(xiàn)方式,被擠下線,我的是:
                    //session發(fā)送改變,表示別處登錄
                    //被擠下線,清除session,提示信息,實現(xiàn)跳轉
                    request.setAttribute("online",false);
                    request.getRequestDispatcher("/logout.do").forward(request,response);
                    return;
                }
                chain.doFilter(new XssHttpSerlet((HttpServletRequest) request), response);

    <filter>
        <filter-name>LoginLimitFilter</filter-name>
        <filter-class>io.github.brightloong.loginlimite.LoginLimitFilter</filter-class>
    </filter>
    <filter-mapping>
        <filter-name>LoginLimitFilter</filter-name>
        <url-pattern>/*</url-pattern>
    </filter-mapping>