Socket 통신(Thread 필수)

* MainActivity.java

public class MainActivity extends AppCompatActivity {

    EditText input1;
    TextView output1;

    int port = 5001;

    Handler handler = new Handler();

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);

        input1 = findViewById(R.id.input1);
        output1 = findViewById(R.id.output1);

        Button sendButton = findViewById(R.id.sendButton);
        sendButton.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {
                final String data = input1.getText().toString();

                new Thread(new Runnable() {
                    @Override
                    public void run() {
                        send(data); // data 변수 접근을 위해 final 선언
                    }
                }).start();
            }
        });

        Button startServerButton = findViewById(R.id.startServerButton);
        startServerButton.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {
                new Thread(new Runnable() {
                    @Override
                    public void run() {
                        startServer();
                    }
                }).start();
            }
        });
    }

    public void startServer() {
        try {
            ServerSocket server = new ServerSocket(port);

            while (true) {
                Socket socket = server.accept();
                InetAddress clientHost = socket.getInetAddress();
                int clientPort = socket.getPort();
                println("클라이언트 연결됨 : " + clientHost + ", " + clientPort);

                ObjectInputStream inputStream = new ObjectInputStream(socket.getInputStream());
                String input = (String) inputStream.readObject();
                println("데이터 받음 : " + input);

                ObjectOutputStream outputStream = new ObjectOutputStream(socket.getOutputStream());
                outputStream.writeObject(input + " from server.");
                outputStream.flush();
                println("데이터 보냄");

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

    public void println(final String data) {
        handler.post(new Runnable() {
            @Override
            public void run() {
                output1.append(data + "\n");
            }
        });
    }

    public void send(String data) {
        try {
            Socket socket = new Socket("localhost", port);

            ObjectOutputStream outputStream = new ObjectOutputStream(socket.getOutputStream());
            outputStream.writeObject(data);
            outputStream.flush();

            ObjectInputStream inputStream = new ObjectInputStream(socket.getInputStream());
            String input = (String) inputStream.readObject();
            socket.close();
        } catch (Exception e) {
            e.printStackTrace();
        }
    }

}

* activity_main.xml

<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:app="http://schemas.android.com/apk/res-auto"
    xmlns:tools="http://schemas.android.com/tools"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    android:orientation="vertical"
    tools:context=".MainActivity" >

    <LinearLayout
        android:layout_width="match_parent"
        android:layout_height="0dp"
        android:layout_weight="1"
        android:background="#80D8FF"
        android:orientation="vertical">

        <TextView
            android:id="@+id/textView"
            android:textSize="30sp"
            android:layout_marginBottom="30dp"
            android:layout_width="match_parent"
            android:layout_height="wrap_content"
            android:text="클라이언트" />

        <EditText
            android:id="@+id/input1"
            android:layout_width="match_parent"
            android:layout_height="wrap_content"
            android:ems="10"
            android:inputType="textPersonName" />

        <Button
            android:id="@+id/sendButton"
            android:layout_width="match_parent"
            android:layout_height="wrap_content"
            android:text="전송" />

    </LinearLayout>

    <LinearLayout
        android:layout_width="match_parent"
        android:layout_height="0dp"
        android:layout_weight="1"
        android:background="#FFFF8D"
        android:orientation="vertical">

        <TextView
            android:id="@+id/textView2"
            android:textSize="30sp"
            android:layout_marginBottom="30dp"
            android:layout_width="match_parent"
            android:layout_height="wrap_content"
            android:text="서버" />

        <Button
            android:id="@+id/startServerButton"
            android:layout_width="match_parent"
            android:layout_height="wrap_content"
            android:text="서버 시작" />

        <ScrollView
            android:layout_width="match_parent"
            android:layout_height="match_parent">

            <LinearLayout
                android:layout_width="match_parent"
                android:layout_height="wrap_content"
                android:orientation="vertical" >

                <TextView
                    android:id="@+id/output1"
                    android:textSize="20sp"
                    android:layout_width="match_parent"
                    android:layout_height="wrap_content" />
            </LinearLayout>
            
        </ScrollView>

    </LinearLayout>

</LinearLayout>

* AndroidManifest.xml

<uses-permission android:name="android.permission.INTERNET" />