Java 13 の新しい HttpClient を使用した WebSocket リクエストの送信と応答の処理

import java.net.URI;
import java.net.http.HttpClient;
import java.net.http.WebSocket;
import java.net.http.WebSocket.Builder;

public class WebSocketClient {
    public static void main(String[] args) {
        HttpClient client = HttpClient.newHttpClient();
        WebSocket.Builder builder = client.newWebSocketBuilder();

        // 设置WebSocket服务器的URI
        URI uri = URI.create("ws://localhost:8080/websocket");

        // 创建WebSocket连接
        WebSocket ws = builder.buildAsync(uri, new WebSocketListener()).join();

        // 发送消息到WebSocket服务器
        ws.sendText("Hello, WebSocket!");

        // 关闭WebSocket连接
        ws.sendClose(WebSocket.NORMAL_CLOSURE, "Done");
    }

    static class WebSocketListener implements WebSocket.Listener {
        @Override
        public void onOpen(WebSocket webSocket) {
            System.out.println("Connected to server");
        }

        @Override
        public CompletionStage<?> onText(WebSocket webSocket, CharSequence data, boolean last) {
            System.out.println("Received message: " + data);
            return null;
        }

        @Override
        public CompletionStage<?> onClose(WebSocket webSocket, int statusCode, String reason) {
            System.out.println("Closed: " + statusCode + " " + reason);
            return null;
        }

        @Override
        public void onError(WebSocket webSocket, Throwable error) {
            System.out.println("Error: " + error.getMessage());
        }
    }
}