opcUa连接方式java种基于Milo SDK的连接方式代码

以下是基于Milo SDK的Java代码示例，连接到OPC UA服务器并读取节点值：

import org.eclipse.milo.opcua.sdk.client.OpcUaClient;
import org.eclipse.milo.opcua.sdk.client.api.config.OpcUaClientConfig;
import org.eclipse.milo.opcua.sdk.client.api.identity.UsernameProvider;
import org.eclipse.milo.opcua.stack.core.security.SecurityPolicy;
import org.eclipse.milo.opcua.stack.core.types.structured.EndpointDescription;
import org.eclipse.milo.opcua.stack.core.types.structured.UserTokenPolicy;

import java.util.List;
import java.util.concurrent.CompletableFuture;

public class OpcUaClientExample {

    public static void main(String[] args) throws Exception {
        // 连接参数
        String endpointUrl = "opc.tcp://localhost:12685/example";
        String username = "user";
        String password = "password";

        // 创建OpcUaClientConfig
        OpcUaClientConfig config = OpcUaClientConfig.builder()
                .setEndpoint(getEndpoint(endpointUrl))
                .setIdentityProvider(getIdentityProvider(username, password))
                .setSecurityPolicy(SecurityPolicy.Basic256Sha256)
                .setRequestTimeout(uint(5000))
                .build();

        // 创建OpcUaClient
        OpcUaClient client = OpcUaClient.create(config);

        // 连接服务器
        CompletableFuture<Void> future = client.connect();
        future.get();

        // 读取节点值
        String nodeToRead = "ns=2;s=MyVariable";
        CompletableFuture<DataValue> readFuture = client.readValue(0, TimestampsToReturn.Both, nodeToRead);
        DataValue value = readFuture.get();

        System.out.println("Value: " + value.getValue().getValue());

        // 断开连接
        CompletableFuture<Void> closeFuture = client.disconnect();
        closeFuture.get();
    }

    /**
     * 获取EndpointDescription
     */
    private static EndpointDescription getEndpoint(String endpointUrl) throws Exception {
        List<EndpointDescription> endpoints = DiscoveryClient.getEndpoints(endpointUrl).get();
        EndpointDescription endpoint = endpoints.stream()
                .filter(e -> e.getSecurityPolicyUri().equals(SecurityPolicy.Basic256Sha256.getUri()))
                .findFirst().orElseThrow(() -> new Exception("no desired endpoints returned"));
        return endpoint;
    }

    /**
     * 获取IdentityProvider
     */
    private static UsernameProvider getIdentityProvider(String username, String password) {
        UserTokenPolicy userTokenPolicy = new UserTokenPolicy(null, null, null, null);
        return new UsernameProvider(username, password, userTokenPolicy);
    }

    /**
     * 将int转为UnsignedInteger
     */
    private static UnsignedInteger uint(int value) {
        return Unsigned.uint(value);
    }
}

在这个示例中，我们先创建了一个OpcUaClientConfig对象，该对象包含了连接OPC UA服务器的参数，如服务器地址、用户名、密码、安全策略等。然后创建一个OpcUaClient对象，并使用connect()方法连接服务器。之后，我们使用readValue()方法读取指定节点的值，并使用disconnect()方法断开连接。