How to connect to Mqtt3AsyncClient using HiveMq-mqtt library?

Steps to Connect to Mqtt3AsyncClient Using the HiveMQ MQTT Library

Step 1: Add Maven Dependency

First, ensure your project includes the HiveMQ MQTT client library. If using Maven, add the following dependency to your pom.xml file:

xml
<dependency>
    <groupId>com.hivemq</groupId>
    <artifactId>hivemq-mqtt-client</artifactId>
    <version>1.2.1</version>
</dependency>

Check for the latest version to ensure you are using the most recent library.

Step 2: Create Mqtt3AsyncClient Instance

Create an instance of Mqtt3AsyncClient using the HiveMQ MQTT client library. This can be achieved with the MqttClient.builder() method:

java
import com.hivemq.client.mqtt.mqtt3.Mqtt3AsyncClient;
import com.hivemq.client.mqtt.MqttClient;
import com.hivemq.client.mqtt.mqtt3.Mqtt3ClientBuilder;

public class MqttExample {
    public static void main(String[] args) {
        Mqtt3AsyncClient client = MqttClient.builder()
            .useMqttVersion3()
            .identifier(UUID.randomUUID().toString()) // Client identifier
            .serverHost("broker.hivemq.com") // MQTT server address
            .serverPort(1883) // MQTT server port
            .buildAsync();
    }
}

Step 3: Connect to MQTT Server

Use the connect method to asynchronously connect to the MQTT server. You can also add additional connection options using Mqtt3Connect, such as clean session and keep-alive interval.

java
import com.hivemq.client.mqtt.mqtt3.message.connect.connack.Mqtt3ConnAck;

public class MqttExample {
    public static void main(String[] args) {
        // Create Mqtt3AsyncClient instance
        Mqtt3AsyncClient client = MqttClient.builder()
            .useMqttVersion3()
            .identifier(UUID.randomUUID().toString())
            .serverHost("broker.hivemq.com")
            .serverPort(1883)
            .buildAsync();

        // Asynchronously connect to MQTT server
        client.connectWith()
            .cleanSession(true)
            .keepAlive(10)
            .send()
            .whenComplete((connAck, throwable) -> {
                if (throwable != null) {
                    System.out.println("Connection failed: " + throwable.getMessage());
                } else {
                    System.out.println("Connected successfully: " + connAck);
                    // Handling after connection
                }
            });
    }
}

Step 4: Handle Business Logic After Connection

After successfully connecting to the server, begin subscribing to topics or publishing messages. For example, subscribe to a topic:

java
client.subscribeWith()
    .topicFilter("test/topic")
    .callback(publish -> {
        System.out.println("Received message: " + new String(publish.getPayloadAsBytes()));
    })
    .send()
    .whenComplete((subAck, throwable) -> {
        if (throwable != null) {
            System.out.println("Subscription failed: " + throwable.getMessage());
        } else {
            System.out.println("Subscription successful");
        }
    });

The following are the basic steps for connecting and interacting with Mqtt3AsyncClient using the HiveMQ MQTT library. With this client library, you can flexibly handle various MQTT-related business requirements, such as device communication and IoT data exchange.