服务端

 public static void main(String[] args) throws IOException {

        int port = 30000;//端口号
        //1、创建ServerSocket 绑定监听端口
        ServerSocket serverSocket = new ServerSocket(port);
        //2、调用accept方法开始监听，客户端连接后，返回Socket
        System.out.println("====等待客户端连接=======");
        Socket socket = serverSocket.accept();
        //3、连接成功后，获取InputStream，读取客户端发来信息
        System.out.println("===已连接：" + socket.isConnected() + "======");
        try {
            BufferedReader br = new BufferedReader(new InputStreamReader(socket.getInputStream()));
            //4、当获取的信息不为exit时，循环接收
            while (true) {
                String info = br.readLine();
                if (!info.isEmpty()) {
                    System.out.println(info);
                }
                if (info.equals("exit")) {
                    br.close();
                    break;
                }
            }

        } catch (Exception e) {
            e.printStackTrace();
        } finally {
            socket.close();
            serverSocket.close();
        }
    }

客户端

   //端口号和服务端地址
        int port = 30000;
        InetAddress  address = InetAddress.getLocalHost();//获取本地地址

        //1、获取访问服务端的Socket对象，建立与服务端的连接
        Socket socket = new Socket(address,port);
        System.out.println("=====已连接："+ socket.isConnected()+"======");
        //是否连接
        //2、获取输出流
        OutputStream  out =  socket.getOutputStream();
        PrintWriter pw = new PrintWriter(out,true);
        String message ="您好，服务端！";
        pw.println(message);
        //3、自己输入信息，发送给服务端，并获得响应
        Scanner scanner = new Scanner(System.in);
        while(true){
            String s = scanner.nextLine();
            pw.println(s);
            if(s.equals("exit")){
                break;
            }
        }
        out.close();
        pw.close();
        socket.close();

Android Studio 不支持在同一个模块中运行两个JAVA 程序，它们的运行是同步的，因此需要重开一个Android Project.