# chatting program 구현 / 네트워크 교육과정 (4일차)

 간단한 채팅 프로그램 만들기

- 다대다 클라이언트 간의 채팅

- 서버는 클라이언트에게 메시지를 뿌려주는 역할

[Server]

package tcp4;


import java.io.BufferedInputStream;
import java.io.BufferedOutputStream;
import java.io.IOException;
import java.net.ServerSocket;
import java.net.Socket;
import java.util.ArrayList;
import java.util.List;


public class Server {


	ServerSocket serSock;
	List<Socket> sockList;


	public Server() throws IOException {
		serSock = new ServerSocket(10081);
		sockList = new ArrayList<>();
	}


	public void all_client_write(Socket sock, String msg) {


		BufferedOutputStream bos = null;
		try {
			String info = "[" + sock.getRemoteSocketAddress() + "] : ";
			for (int i = 0; i < sockList.size(); i++) {
				bos = new BufferedOutputStream(sockList.get(i).getOutputStream());
				System.out.println("send to " + sockList.get(i).toString() + ":" + msg);


				String inFoMsg = info + msg;
				bos.write(inFoMsg.getBytes("UTF-8"));
				bos.flush();


			}


		} catch (IOException e) {
			// TODO Auto-generated catch block
			try {
				bos.close();
				sock.close();
				removeSock(sock);
			} catch (IOException e1) {
				// TODO Auto-generated catch block
				e1.printStackTrace();
			}


			System.out.println("server write exception!");


			e.printStackTrace();
		}


	}


	public void stop(Thread thread) {
		thread.interrupt();
	}
	public void removeSock(Socket sock) {
		System.out.println("socket is close");
		System.out.println("====================================");
		System.out.println("현재 접속: " + sockList.size());
		for (int i = 0; i < sockList.size(); i++) {
			if (sockList.get(i) == sock) {
				try {
					sockList.get(i).close();
					sockList.remove(i);
					break;
				} catch (IOException e1) {
					// TODO Auto-generated catch block
					e1.printStackTrace();
				}


			}
		}
		for (int i = 0; i < sockList.size(); i++) {
			System.out.println(sockList.get(i).toString());
		}
		System.out.println("====================================\n\n");


	}


	public void read(Socket sock) {
		Thread thread = null;


		thread = new Thread(new Runnable() {


			@Override
			public void run() {
				// TODO Auto-generated method stub
				BufferedInputStream bis = null;
				boolean flag = true;
				try {
					while (flag) {


						bis = new BufferedInputStream(sock.getInputStream());
						byte b[] = new byte[256];
						int data = bis.read(b);


						if (data != 0) {
							String msg = new String(b);
							System.out.println("[" + sock.getLocalAddress() + "] : " + msg);


							all_client_write(sock, msg);
						}


					}
				} catch (IOException e) {
					// TODO Auto-generated catch block
					try {
						sock.close();
						removeSock(sock);
					} catch (IOException e2) {
						// TODO Auto-generated catch block
						e2.printStackTrace();
					}
				}


			}


		});


		thread.start();


	}


	public void startServer() {
		System.out.println("start Server!");
		Thread thread = new Thread(new Runnable() {


			@Override
			public void run() {
				// TODO Auto-generated method stub
				try {
					while (true) {
						Socket sock = null;
						sock = serSock.accept();
						sockList.add(sock);


						System.out.println("====================================");
						System.out.println("현재 접속: " + sockList.size());
						for (int i = 0; i < sockList.size(); i++) {
							System.out.println(sockList.get(i).toString());
						}
						System.out.println("====================================\n\n");


						read(sock);
					}


				} catch (IOException e) {
					// TODO Auto-generated catch block
					e.printStackTrace();
					System.out.println("socket accept excpetion");
					return;
				}
			}
		});
		thread.start();


	}


	public static void main(String[] args) {
		// TODO Auto-generated method stub
		try {
			new Server().startServer();
		} catch (IOException e) {
			// TODO Auto-generated catch block
			e.printStackTrace();
			System.out.println("server start exception");
		}
	}


}

[Client]

package tcp4;


import java.io.BufferedInputStream;
import java.io.BufferedOutputStream;
import java.io.IOException;
import java.net.InetSocketAddress;
import java.net.Socket;
import java.net.UnknownHostException;
import java.util.Scanner;


public class Client {


	Socket sock;
	String host;
	int port;


	public void connect() throws UnknownHostException, IOException {
		host = "localhost";
		port = 10081;
		sock = new Socket();
		sock.connect(new InetSocketAddress(host, port));
	}


	public void read() {
		Thread thread = new Thread(new Runnable() {


			@Override
			public void run() {
				// TODO Auto-generated method stub
				BufferedInputStream bis = null;
				try {
					while (true) {


						bis = new BufferedInputStream(sock.getInputStream());
						byte[] b = new byte[256];
						int data = bis.read(b);


						if (data != 0) {
							System.out.println("\n");
							System.out.println(new String(b));
						}
					}
				} catch (IOException e) {
					// TODO Auto-generated catch block


					System.out.println("client read exception!");
					e.printStackTrace();


					try {
						
						bis.close();
						sock.close();
						
					} catch (IOException e1) {
						// TODO Auto-generated catch block
						e1.printStackTrace();
					}
			
				}
			}
		});
		thread.start();
	}


	public void chatStart() {
		Scanner scan = new Scanner(System.in);
		BufferedOutputStream bos=null;
		while (true) {
			System.out.print("입력>>");
		String msg = scan.nextLine();


		try {
			bos = new BufferedOutputStream(sock.getOutputStream());
			bos.write(msg.getBytes("UTF-8"));
			bos.flush();
		} catch (IOException e) {
			// TODO Auto-generated catch block


			System.out.println("client write exception!");
			try {
				bos.close();
				sock.close();
				break;
			} catch (IOException e1) {
				// TODO Auto-generated catch block
				e1.printStackTrace();
			}
			e.printStackTrace();
		}
	
		
		}
	}


	public static void main(String[] args) {
		// TODO Auto-generated method stub
		Client client = new Client();
		try {
			client.connect();
		} catch (IOException e) {
			// TODO Auto-generated catch block
			e.printStackTrace();
			System.out.println("connect exception");
		}
		client.read();
		client.chatStart();
	}


}

====> 결과

소켓이 close() 됐을 때의 예외처리는 무엇보다 중요하다.

반드시 예외를 잡고 처리해야한다. 

시간이 없어서 빈약하게 처리했지만, 로직을 작성하는 것보다 메모리 누수 혹은 정확한 처리가 더 중요한 것 같다.

다음은 selector 와  asyncrhronousServerSocket에 대해 마지막으로 알아보자.

https://docs.oracle.com/javase/7/docs/api/java/nio/channels/AsynchronousServerSocketChannel.html