以上代码结合opcua订阅实现实时数据传输给前端

好的，结合OPC UA订阅和WebSocket实现实时数据传输给前端的示例代码如下：

import org.eclipse.milo.opcua.sdk.client.OpcUaClient;
import org.eclipse.milo.opcua.sdk.client.api.subscriptions.UaMonitoredItem;
import org.eclipse.milo.opcua.sdk.client.api.subscriptions.UaSubscription;
import org.eclipse.milo.opcua.stack.core.AttributeId;
import org.eclipse.milo.opcua.stack.core.Identifiers;
import org.eclipse.milo.opcua.stack.core.types.builtin.DataValue;
import org.eclipse.milo.opcua.stack.core.types.builtin.NodeId;
import org.eclipse.milo.opcua.stack.core.types.enumerated.TimestampsToReturn;

import javax.websocket.OnClose;
import javax.websocket.OnError;
import javax.websocket.OnOpen;
import javax.websocket.Session;
import javax.websocket.server.ServerEndpoint;
import java.io.IOException;
import java.util.concurrent.CompletableFuture;
import java.util.concurrent.ExecutionException;

@ServerEndpoint("/websocket")
public class MyWebSocketServer {

    private OpcUaClient client;
    private UaSubscription subscription;
    private UaMonitoredItem item;
    private Session session;

    @OnOpen
    public void onOpen(Session session) throws Exception {
        System.out.println("WebSocket opened: " + session.getId());
        this.session = session;

        // 连接OPC UA服务器
        CompletableFuture<OpcUaClient> future = OpcUaClient.create(
                "opc.tcp://localhost:12685/sample",
                endpoints -> endpoints.stream().findFirst(),
                config -> {
                    config.setApplicationName("OPC UA Client");
                    config.setCertificateValidationEnabled(false);
                }
        );

        client = future.get();

        // 订阅变量
        subscription = client.getSubscriptionManager().createSubscription(1000.0);
        NodeId nodeId = new NodeId(2, "Sensor");
        item = subscription.createMonitoredItem(
                new UaMonitoredItem.Parameters(
                        nodeId,
                        AttributeId.Value,
                        TimestampsToReturn.Both
                )
        );

        item.setValueConsumer(this::onDataChanged);
    }

    private void onDataChanged(UaMonitoredItem item, DataValue value) {
        try {
            // 发送数据到前端
            session.getBasicRemote().sendText(value.getValue().getValue().toString());
        } catch (IOException e) {
            e.printStackTrace();
        }
    }

    @OnClose
    public void onClose(Session session) throws Exception {
        System.out.println("WebSocket closed: " + session.getId());

        // 断开OPC UA连接
        item.delete();
        subscription.delete();
        client.disconnect().get();
    }

    @OnError
    public void onError(Throwable error) {
        System.err.println("WebSocket error: " + error.getMessage());
    }
}

在上面的代码中，使用`OpcUaClient`连接到OPC UA服务器。然后，创建一个订阅并订阅变量。当变量的值发生变化时，调用`onDataChanged`方法将值发送到前端。最后，在WebSocket连接关闭时，断开OPC UA连接。

请注意，此代码仅用于示例目的。在实际应用中，应该考虑更多的错误处理和线程安全问题。