rcomp-mqtt/src/main/java/component/mqtt/MqttComponent.java

package component.mqtt;

import java.util.HashSet;
import java.util.Set;

import org.eclipse.paho.client.mqttv3.MqttClient;
import org.eclipse.paho.client.mqttv3.MqttException;
import org.eclipse.paho.client.mqttv3.persist.MemoryPersistence;
import org.osgi.service.component.annotations.Activate;
import org.osgi.service.component.annotations.Component;
import org.osgi.service.component.annotations.Deactivate;
import org.osgi.service.metatype.annotations.ObjectClassDefinition;
import org.reactivestreams.Publisher;
import org.reactivestreams.Subscriber;

import component.api.MComponent;

@Component(property="name=mqtt")
public class MqttComponent implements MComponent {
    
    MqttClient client;
    private Set<MqttDestination<?>> destinations = new HashSet<>();

    @ObjectClassDefinition(name = "MQTT config")
    @interface MqttConfig {
        String serverUrl() default "tcp://localhost:1883";
        String clientId();
    }
    
    @Activate
    public void activate(MqttConfig config) throws MqttException {
        client = new MqttClient(config.serverUrl(), MqttClient.generateClientId(),
                                new MemoryPersistence());
        client.connect();
    }
    
    @Deactivate
    public void deactivate() throws MqttException {
        for (MqttDestination<?> destination : destinations) {
            try {
                destination.close(); 
            } catch (Exception e) {
            }
        }
        client.disconnect();
        client.close();
    }

    @Override
    public <T> Publisher<T> from(String topic, Class<T> type) {
        return new MqttSource<T>(client, topic, type);
    }  
    
    @Override
    public <T> Subscriber<T> to(String topic, Class<T> type) {
        MqttDestination<T> destination = new MqttDestination<T>(client, topic, type);
        destinations.add(destination);
        return destination;
    }

}