编写一个OpcUaClient客户端的java示例

以下是一个简单的Java OPC UA客户端示例代码：

import java.util.concurrent.CompletableFuture;
import java.util.concurrent.ExecutionException;

import org.eclipse.milo.opcua.sdk.client.OpcUaClient;
import org.eclipse.milo.opcua.sdk.client.api.identity.UsernameProvider;
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;

public class OPCUAClient {

    public static void main(String[] args) throws Exception {
        String endpointUrl = "opc.tcp://localhost:12686/example";
        OpcUaClient client = new OpcUaClient(endpointUrl);
        client.setIdentityProvider(new UsernameProvider("user", "password"));

        CompletableFuture<Void> future = client.connect().thenCompose(v -> {
            NodeId nodeId = new NodeId(2, "/Static/AllProfiles/Scalar/Int32");
            return client.readValue(0, TimestampsToReturn.Both, nodeId);
        }).thenCompose(dataValue -> {
            System.out.println("Value: " + dataValue.getValue().getValue());
            return client.disconnect();
        }).exceptionally(ex -> {
            ex.printStackTrace();
            return null;
        });

        future.get();
    }

}

请注意，此示例仅用于演示目的。在实际应用中，您需要根据您的需要进行修改。