일단 1:1 소켓 통신 예제에 대해 살펴보도록 하자.

소켓 간 연결 (클라이언트-서버)

Client.java

import java.io.IOException;
import java.net.InetSocketAddress;
import java.net.Socket;

public class ClientExample {
    public static void main(String[] args) {
        Socket socket = null;

        try {
            socket = new Socket();
            System.out.println("[연결 요청]");
            socket.connect(new InetSocketAddress("localhost", 5001));
            System.out.println("[연결 성공]");
        } catch (IOException e) {
            e.printStackTrace();
        }

        if (!socket.isClosed()) {
            try {
                socket.close();
            } catch (IOException e) {
                e.printStackTrace();
            }
        }
    }
}

Server.java

import java.io.IOException;
import java.net.InetSocketAddress;
import java.net.ServerSocket;
import java.net.Socket;

public class ServerExample {
    public static void main(String[] args) {
        ServerSocket serverSocket = null;

        try {
            serverSocket = new ServerSocket();
            serverSocket.bind(new InetSocketAddress("localhost", 5001));

            while (true) {
                System.out.println("[연결 기다림]");
                Socket socket = serverSocket.accept();
                InetSocketAddress isa = (InetSocketAddress) socket.getRemoteSocketAddress();
                System.out.println("[연결 수락함] " + isa.getHostName());
            }
        } catch (IOException e) {
            e.printStackTrace();
        }

        if (!serverSocket.isClosed()) {
            try {
                serverSocket.close();
            } catch (IOException e) {
                e.printStackTrace();
            }
        }
    }
}

데이터 송수신까지 해보자

Client.java

import java.io.IOException;
import java.io.InputStream;
import java.io.OutputStream;
import java.net.InetSocketAddress;
import java.net.Socket;

public class ClientExample {
    public static void main(String[] args) {
        Socket socket = null;

        try {
            socket = new Socket();
            System.out.println("[연결 요청]");
            socket.connect(new InetSocketAddress("localhost", 5001));
            System.out.println("[연결 성공]");

            byte[] bytes = null;
            String message = null;

            OutputStream os = socket.getOutputStream();
            message = "Hello Server";
            bytes = message.getBytes("UTF-8");
            os.write(bytes);
            os.flush();
            System.out.println("[데이터 보내기 성공]");

            InputStream is = socket.getInputStream();
            bytes = new byte[100];
            int readByteCount = is.read(bytes);
            message = new String(bytes, 0, readByteCount, "UTF-8");
            System.out.println("[데이터 받기 성공] " + message);

            os.close(); is.close();
        } catch (IOException e) {
            e.printStackTrace();
        }

        if (!socket.isClosed()) {
            try {
                socket.close();
            } catch (IOException e) {
                e.printStackTrace();
            }
        }
    }
}

Server.java

public class ServerExample {
    public static void main(String[] args) {
        ServerSocket serverSocket = null;

        try {
            serverSocket = new ServerSocket();
            serverSocket.bind(new InetSocketAddress("localhost", 5001));

            while (true) {
                System.out.println("[연결 기다림]");
                Socket socket = serverSocket.accept();
                InetSocketAddress isa = (InetSocketAddress) socket.getRemoteSocketAddress();
                System.out.println("[연결 수락함] " + isa.getHostName());

                byte[] bytes = null;
                String message = null;

                InputStream is = socket.getInputStream();
                bytes = new byte[100];
                int readByteCount = is.read(bytes); // blocking
                message = new String(bytes, 0, readByteCount, "UTF-8");
                System.out.println("[데이터 받기 성공] " + message);

                OutputStream os = socket.getOutputStream();
                message = "Hello Client";
                bytes = message.getBytes("UTF-8");
                os.write(bytes);
                os.flush();
                System.out.println("[데이터 보내기 성공]");

                is.close(); os.close(); socket.close();
            }
        } catch (IOException e) {
            e.printStackTrace();
        }

        if (!serverSocket.isClosed()) {
            try {
                serverSocket.close();
            } catch (IOException e) {
                e.printStackTrace();
            }
        }
    }
}

다음시간에는 멀티쓰레드의 개념에 대해 복습하고, 멀티쓰레드를 활용해 Java TCP 소켓 프로그래밍을 통한 간단한 채팅프로그램을 만들어보자 ! 사실 만드는건 아니고 예제 분석하기 ㅎㅎ