WebSocket错误：java.lang.IllegalStateException: The WebSocket session [1] has been closed and no method (apart from close()) may be called on a closed session

　主要原因：在建立连接存储对象信息的时候保存了用户ID，在断开连接时移除当前对象失败。

private static CopyOnWriteArraySet<AcceptWebSocket> webSocketSet = new CopyOnWriteArraySet<>();

@OnOpen

public void onOpen(@PathParam("userid") Integer id, Session session) {

    this.session = session;
    this.userid = id;
    webSocketSet.put(userid, this);//用户id 和session绑定
    logger.info("【新的socket连接】");
}

修改：通过判断所有登录的用户是否属于当前用户组，实现单发或者群发。

/**
 * 打开连接时
 *
 * @param session
 */
@OnOpen
public void onOpen(@PathParam("userid") Integer userid, Session session) {
    this.session = session;
    this.work = userService.selectUserId(userid);
    webSocketSet.add(this);
    logger.info("【新的socket连接】");
}

/**
 * 向所有连接客户端推送消息
 */
public  void sendWebSocketMessage(String message) {
    try {
        if (webSocketSet.size() != 0) {
            for (AcceptWebSocket p : webSocketSet) {
                if (p != null && p.work == 3) {
                    p.session.getBasicRemote().sendText(message);
                }
            }
        }
    } catch (IOException e) {
        e.printStackTrace();
    }
}

/**
 * 关闭连接时
 */
@OnClose
public void onClose() {
    webSocketSet.remove(this);
    logger.info("【socket连接关闭】");
}