자바 소켓 프로그래밍 예제(채팅 프로그램)

메인 서버 

package chat;
 
import java.io.IOException;
import java.io.Writer;
import java.net.InetAddress;
import java.net.InetSocketAddress;
import java.net.ServerSocket;
import java.net.Socket;
import java.net.SocketException;
import java.util.ArrayList;
import java.util.List;
 
public class ChatServer {
 
    private static ServerSocket serverSocket;
    private static final int SERVER_PORT = 5000;
    
    public static void main(String[] args) {
        
        try {
            List<Writer> listWriters = new ArrayList<>();
            serverSocket = new ServerSocket();
            String ipAddress = InetAddress.getLocalHost().getHostAddress();
            serverSocket.bind(new InetSocketAddress(ipAddress, SERVER_PORT));
            consoleLog( "binding " +  ipAddress + ":" + SERVER_PORT );
 
            while(true) {
                Socket socket = serverSocket.accept();
                new ChatServerProcessThread(socket, listWriters).start();
            }
            
        } catch (SocketException e) {
            System.out.println("[server] socket connect failed");
        } catch (IOException e) {
            e.printStackTrace();
        }
    }
 
    private static void consoleLog(String log) {
        System.out.println("[server] : " + log);
    }
}
 

서버를 가지고 통신을 할 수 있도록 ServerSocket 객체를 선언했습니다. 

bind이라는 것은 소켓에 ip와 포트를 할당할 수 있도록 연결해주는 역할을 합니다. 

그리고 accept는 클라이언트가 올 때까지 기다립니다. 만약에 클라이언트가 오게 된다면 "ChatServerProcessThread"라는 쓰레드 객체가 만들어지면서 시작하게 됩니다. 

서버에서 돌아가는 쓰레드

package chat;
 
import java.io.BufferedReader;
import java.io.IOException;
import java.io.InputStreamReader;
import java.io.OutputStreamWriter;
import java.io.PrintWriter;
import java.io.Writer;
import java.net.InetSocketAddress;
import java.net.Socket;
import java.net.SocketException;
import java.util.List;
 
public class ChatServerProcessThread extends Thread{
 
    private Socket socket;
    private String nickname;
    private List<Writer> listWriters;
    
    public ChatServerProcessThread(Socket socket, List<Writer> listWriters) {
        this.socket = socket;
        this.listWriters = listWriters;
    }
 
    @Override
    public void run() {
        
        InetSocketAddress remoteSocketAddress = (InetSocketAddress) socket.getRemoteSocketAddress();
        int remoteHostPort = remoteSocketAddress.getPort();
        String remoteHostAddress = remoteSocketAddress.getAddress().getHostAddress();
        consoleLog("connected from " + remoteHostAddress + ":" + remoteHostPort);
            
        try {
            PrintWriter pw = new PrintWriter(new OutputStreamWriter(socket.getOutputStream(), "UTF-8"), true);
            BufferedReader br = new BufferedReader(new InputStreamReader(socket.getInputStream(), "UTF-8"));
            
            while(true) {
                String request = br.readLine();
                String tokens[] = request.split(":");
                
                if("join".equals(tokens[0])) {
                    doJoin(pw, tokens[1]);
                } else if("message".equals(tokens[0])) {
                    doMessage(tokens[1]);
                } else if("quit".equals(tokens[0])) {
                    doQuit(pw);
                    break;
                }
                
            }
            
        } catch(SocketException e) {
            System.out.println("[server] socket disconnected");
        } catch(IOException e) {
            e.printStackTrace();
        } finally {
            try {
                if(socket != null && !socket.isClosed()) {
                    socket.close();
                }
            } catch (IOException e) {
                e.printStackTrace();
            }
        }
        
    }
    
    private void doQuit(PrintWriter pw) throws IOException {
        removeWriter(pw);
        String data = nickname + "님이 종료되었습니다.";
        broadcast(data);
    }
 
    private void removeWriter(PrintWriter pw) {
        listWriters.remove(pw);
    }
 
    private void doMessage(String message) throws IOException {
        String data = nickname + ":" + message;
        broadcast(data);
    }
 
    private void doJoin(Writer writer, String nickname) throws IOException {
        this.nickname = nickname;
        String message = nickname + "이(가) 채팅에 참여했습니다.";
        broadcast(message);
 
        addWriter(writer);
        
        ((PrintWriter) writer).println("join:ok");
        writer.flush();
    }
 
    private void addWriter(Writer writer) {
        synchronized (listWriters) {
            listWriters.add(writer);
        }
    }
 
    private void broadcast(String message) throws IOException {
        synchronized (listWriters) {
            for(Writer writer : listWriters) {
                ((PrintWriter) writer).println(message);
                writer.flush();
            }
        }
    }
 
    private void consoleLog(String log) {
        System.out.println("[client :" + getId() + "] " + log);
    }
    
}