How to reconnect when connection Lost

[SparkingAShift]

package io.emqx;

import org.eclipse.paho.client.mqttv3.IMqttDeliveryToken;
import org.eclipse.paho.client.mqttv3.MqttCallback;
import org.eclipse.paho.client.mqttv3.MqttMessage;

public class OnMessageCallback implements MqttCallback {
public void connectionLost(Throwable cause) {
// 连接丢失后，一般在这里面进行重连
System.out.println("连接断开，可以做重连");
}

public void messageArrived(String topic, MqttMessage message) throws Exception {
    // subscribe后得到的消息会执行到这里面
    System.out.println("接收消息主题:" + topic);
    System.out.println("接收消息Qos:" + message.getQos());
    System.out.println("接收消息内容:" + new String(message.getPayload()));
}

public void deliveryComplete(IMqttDeliveryToken token) {
    System.out.println("deliveryComplete---------" + token.isComplete());
}

}

no “MQTT client” was defined in this code，how to reconnect

https://www.emqx.io/docs/zh/latest/connect-emqx/java.html