java连接物联网关

要连接物联网网关，可以使用Java中的MQTT协议。MQTT（Message Queuing Telemetry Transport）是一个轻量级的消息通讯协议，特别适用于小型设备和移动设备之间的通讯。

下面是一个使用Eclipse Paho MQTT客户端库连接到物联网网关的Java示例代码：

import org.eclipse.paho.client.mqttv3.MqttClient;
import org.eclipse.paho.client.mqttv3.MqttConnectOptions;
import org.eclipse.paho.client.mqttv3.MqttException;
import org.eclipse.paho.client.mqttv3.persist.MemoryPersistence;

public class MqttClientSample {

    public static void main(String[] args) {
        String topic = "iot-2/type/device_type/id/device_id/cmd/command_id/fmt/format_string";
        String content = "Hello, World!";
        int qos = 2;
        String broker = "tcp://mqtt.example.com:1883";
        String clientId = "JavaSample";
        MemoryPersistence persistence = new MemoryPersistence();

        try {
            MqttClient sampleClient = new MqttClient(broker, clientId, persistence);
            MqttConnectOptions connOpts = new MqttConnectOptions();
            connOpts.setCleanSession(true);
            System.out.println("Connecting to broker: " + broker);
            sampleClient.connect(connOpts);
            System.out.println("Connected");
            System.out.println("Publishing message: " + content);
            sampleClient.publish(topic, content.getBytes(), qos, false);
            System.out.println("Message published");
            sampleClient.disconnect();
            System.out.println("Disconnected");
            System.exit(0);
        } catch (MqttException me) {
            System.out.println("reason " + me.getReasonCode());
            System.out.println("msg " + me.getMessage());
            System.out.println("loc " + me.getLocalizedMessage());
            System.out.println("cause " + me.getCause());
            System.out.println("excep " + me);
            me.printStackTrace();
        }
    }
}

这个示例代码使用了Eclipse Paho MQTT客户端库来连接到一个MQTT代理服务器，并将一条消息发布到指定的主题。你需要替换示例代码中的broker、topic、clientId等参数，以使其与你的环境相匹配。