用java写个websocket

非常好的问题！下面是一个简单的Java WebSocket示例代码：

import java.net.URI;
import java.net.URISyntaxException;
import java.util.Scanner;
import java.util.concurrent.CountDownLatch;
import javax.websocket.ClientEndpoint;
import javax.websocket.CloseReason;
import javax.websocket.ContainerProvider;
import javax.websocket.OnClose;
import javax.websocket.OnMessage;
import javax.websocket.OnOpen;
import javax.websocket.Session;
import javax.websocket.WebSocketContainer;

@ClientEndpoint
public class WebSocketClient {

    private static CountDownLatch latch;
    private static Session session;

    @OnOpen
    public void onOpen(Session session) {
        System.out.println("Connected to server!");
        WebSocketClient.session = session;
        latch.countDown();
    }

    @OnMessage
    public void onMessage(String message) {
        System.out.println("Received message: " + message);
    }

    @OnClose
    public void onClose(CloseReason reason) {
        System.out.println("Connection closed: " + reason);
    }

    public static void main(String[] args) throws URISyntaxException, InterruptedException {
        latch = new CountDownLatch(1);
        WebSocketContainer container = ContainerProvider.getWebSocketContainer();
        String uri = "ws://localhost:8080/websocket";
        container.connectToServer(WebSocketClient.class, new URI(uri));
        latch.await();
        Scanner scanner = new Scanner(System.in);
        while (true) {
            String message = scanner.nextLine();
            session.getBasicRemote().sendText(message);
        }
    }
}

这个示例代码使用了Java的WebSocket API来连接到一个WebSocket服务器，并在控制台上打印收到的消息。你可以将`ws://localhost:8080/websocket`替换为你想要连接的WebSocket服务器的URI。在`main`方法中，我们使用了一个`Scanner`对象来读取用户输入，并将输入的文本发送到服务器。