第一种，PC作为服务器，APP做客户端

    服务端代码：
            try {
        mServerSocket = new ServerSocket(8002);
        while (mCanRun) {
            System.out.println("等待连接..." + mServerSocket.getInetAddress());
            Socket socket = mServerSocket.accept();
            System.out.println("已连接...");
            ReadThread socketThread = new ReadThread(socket);
            if (mList == null) {
                mList = new ArrayList<>();
            }
            mList.add(socketThread);
            socketThread.start();
            
            socketThread.sendMsg("你是第" + mList.size() + "个");
        }
    } catch (Exception e) {
        e.printStackTrace();
    } 
    客户端代码：Socket socket = new Socket("127.0.0.1", 8002); 即可连接成功。