# This is about Java 'network' library

**URL:** <https://discourse.processing.org/t/this-is-about-java-network-library/46291>\
**Category:** Libraries\
**Created:** [April 29, 2025, 11:11am UTC](https://discourse.processing.org/t/this-is-about-java-network-library/46291 "2025-04-29T11:11:31Z")\
**Posts on this page:** 1\
**Showing post:** 8

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**Author:** ![GWAK](https://avatars.discourse-cdn.com/v4/letter/g/13edae/32.png) [@GWAK](https://discourse.processing.org/u/GWAK)\
**Post date:** [May 5, 2025, 2:52am UTC](https://discourse.processing.org/t/this-is-about-java-network-library/46291/8 "2025-05-05T02:52:11Z")

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@glv  
@jafal

I found a practical usage.

1. It can be operated through threads.
2. It can accept multiple users.
3. It was processed using ‘serverEvent’.

It works pretty well, thank you.

```auto
import processing.net.*;
import java.util.concurrent.CopyOnWriteArrayList;

Server server;
CopyOnWriteArrayList<Client> clients = new CopyOnWriteArrayList<Client>();

void setup() {
  size(400, 400);
  server = new Server(this, 5204);
  println("서버 시작됨 (포트 5204)");

  Thread serverThread = new Thread(new Runnable() {
    public void run() {
      handleClients();
    }
  });
  serverThread.start();
}

void draw() {
  background(200);
  text("클라이언트 수: " + clients.size(), 20, 30);
}

// 새로운 클라이언트가 접속되었을 때 호출
void serverEvent(Server someServer, Client newClient) {
  println("접속됨: " + newClient.ip());
  clients.add(newClient);
}

// 비동기 메시지 수신 + 응답 + 연결 종료 처리
void handleClients() {
  while (true) {
    for (Client c : clients) {
      if (!c.active()) {
        println("클라이언트 연결 해제됨: " + c.ip());
        clients.remove(c);
        continue;
      }

      if (c.available() > 0) {
        String msg = c.readStringUntil('\n');
        if (msg != null) {
          msg = msg.trim();
          println("[" + c.ip() + "] 받은 메시지: " + msg);

          // 1) 답문 (예: Echo)
          String reply = "서버 응답: " + msg + "\n";
          c.write(reply);
          println("[" + c.ip() + "] 답문 전송 완료");

          // 2) 특정 키워드가 오면 통신 끊기
          if (msg.equalsIgnoreCase("bye")) {
            println("[" + c.ip() + "] 연결 종료됨 (bye 명령)");
            c.stop(); // 연결 종료
            clients.remove(c); // 리스트에서 제거
          }
        }
      }
    }
    delay(10);
  }
}

```

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