WEBSOCKET報錯：The remote endpoint was in state [TEXT_FULL_WRITING]

報錯：The remote endpoint was in state [TEXT_FULL_WRITING] which is an invalid state for called method 

public void sendMessage(String message) {
        ThreadPoolExecutor cachedThreadPool = ThreadPoolUtil.getCachedThreadPool();
        cachedThreadPool.execute(
          session.getAsyncRemote().sendText(message)
        );
    }

併發衝突，修改後

public void sendMessage(String message) {
        ThreadPoolExecutor cachedThreadPool = ThreadPoolUtil.getCachedThreadPool();
        cachedThreadPool.execute(new Runnable() {
            @Override
            public void run() {
                try {
                    synchronized (session){
                        session.getBasicRemote().sendText(message);
                    }
                } catch (IOException e) {
                    e.printStackTrace();
                }
            }
        });
    }

使用synchronized 對資源加鎖，同時使用線程池優化資源的開銷