Java能接受其他通訊實體連線請求的類是ServerSocket，ServerSocket物件用於監聽客戶端的Socket連線，如果沒有連線，它將一直處於等待狀態。

public class SimpleServer {
    public static void main(String[] args) {
        //建立ServerSocket，用於監聽客戶端Socket的連線請求
        try {
            ServerSocket ss = new ServerSocket(30000);
            while(true)
            {
                System.out
 
.println("有客戶訪問伺服器");
                //每當接受到客戶端Socket的請求時，伺服器端也對應產生一個Socket
                Socket s = ss.accept();
                OutputStream os = s.getOutputStream();
                os.write("Helo,這是伺服器返回的訊息！".getBytes("utf-8"));
                os.close();
                s.close();
            }
        } catch
 
 (IOException e) {
            // TODO Auto-generated catch block
            e.printStackTrace();
        }
    }

}

客戶端程式碼

public class MainActivity extends AppCompatActivity {

    TextView textView;
    Button btn;
    Handler handler;
    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super
 
.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);

        textView = (TextView) findViewById(R.id.show);
        btn = (Button)findViewById(R.id.button);
        handler = new Handler(){
            @Override
            public void handleMessage(Message msg) {
                switch (msg.what)
                {
                    case 0:
                      Bundle bundle;
                      bundle = msg.getData();
                      textView.setText(bundle.getString("result","沒有成功"));
                }
            }
        };
        btn.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View view) {
                new Thread()
                {
                    @Override
                    public void run() {
                        Message msg = handler.obtainMessage();
                        msg.what = 0;

                        Socket socket = null;
                        try {
                            socket = new Socket("10.20.0.1",30000);
                            BufferedReader br = new BufferedReader(new InputStreamReader(socket.getInputStream()));
                            String line = br.readLine();
                            Bundle bundle = new Bundle();
                            bundle.putString("result",line);
                            msg.setData(bundle);
                            br.close();
                            socket.close();
                        } catch (IOException e) {
                            e.printStackTrace();
                        }
                        handler.sendMessage(msg);
                    }
                }.start();
            }
        });

    }
}