Chat Flutter, Spring 활용 채팅 클라이언트 및 서버 참고 https://learnote-dev.com/java/Spring-%EA%B2%8C%EC%8B%9C%ED%8C%90-API-%EB%A7%8C%EB%93%A4%EA%B8%B0-webSocket%EC%9C%BC%EB%A1%9C-%EC%B1%84%ED%8C%85%EC%84%9C%EB%B2%84-%EA%B5%AC%ED%98%84%ED%95%98%EA%B8%B0/