Sending messages to MQTT

The MQTT Connector can write Reactive Messaging Messages as MQTT Message.

Example

Let’s imagine you have a MQTT server/broker running, and accessible using the mqtt:1883 address (by default it would use localhost:1883). Configure your application to write the messages from the prices channel into a MQTT Messages as follows:

mp.messaging.outgoing.prices.type=smallrye-mqtt
mp.messaging.outgoing.prices.host=mqtt
mp.messaging.outgoing.prices.port=1883

1. Sets the connector for the prices channel
2. Configure the broker/server host name.
3. Configure the broker/server port. 1883 is the default.

Note

You don’t need to set the MQTT topic. By default, it uses the channel name (prices). You can configure the topic attribute to override it. NOTE: It is generally recommended to set the client-id. By default, the connector is generating a unique client-id.

Then, your application must send Message<Double> to the prices channel. It can use double payloads as in the following snippet:

package mqtt.outbound;

import java.time.Duration;
import java.util.Random;

import jakarta.enterprise.context.ApplicationScoped;

import org.eclipse.microprofile.reactive.messaging.Outgoing;

import io.smallrye.mutiny.Multi;

@ApplicationScoped
public class MqttPriceProducer {

    private Random random = new Random();

    @Outgoing("prices")
    public Multi<Double> generate() {
        // Build an infinite stream of random prices
        // It emits a price every second
        return Multi.createFrom().ticks().every(Duration.ofSeconds(1))
                .map(x -> random.nextDouble());
    }

}

Or, you can send Message<Double>:

package mqtt.outbound;

import java.time.Duration;
import java.util.Random;

import jakarta.enterprise.context.ApplicationScoped;

import org.eclipse.microprofile.reactive.messaging.Message;
import org.eclipse.microprofile.reactive.messaging.Outgoing;

import io.smallrye.mutiny.Multi;

@ApplicationScoped
public class MqttPriceMessageProducer {

    private Random random = new Random();

    @Outgoing("prices")
    public Multi<Message<Double>> generate() {
        // Build an infinite stream of random prices
        // It emits a price every second
        return Multi.createFrom().ticks().every(Duration.ofSeconds(1))
                .map(x -> Message.of(random.nextDouble()));
    }

}

Serialization

The Message sent to MQTT can have various payload types:

• JsonObject: JSON string encoded as byte[]

• JsonArray: JSON string encoded as byte[]

• java.lang.String and Java primitive types: toString encoded as byte[]

• byte[]

• complex objects: The objects are encoded to JSON and passed as byte[]

Outbound Metadata

The MQTT connector does not provide outbound metadata.

Acknowledgement

MQTT acknowledgement depends on the QoS level. The message is acknowledged when the broker indicated the successful reception of the message (or immediately if the level of QoS does not support acknowledgment).

If a MQTT message cannot be sent to the broker, the message is nacked.

Configuration Reference

Attribute (alias)	Description	Type	Mandatory	Default
auto-clean-session	Set to start with a clean session (true by default)	boolean	false	true
auto-generated-client-id	Set if the MQTT client must generate clientId automatically	boolean	false	true
auto-keep-alive	Set if the MQTT client must handle PINGREQ automatically	boolean	false	true
client-id	Set the client identifier	string	false
client-options-name (mqtt-client-options-name)	The name of the MQTT Client Option bean (io.smallrye.reactive.messaging.mqtt.session.MqttClientSessionOptions) used to customize the MQTT client configuration	string	false
connect-timeout-seconds	Set the connect timeout (in seconds)	int	false	60
health-enabled	Whether health reporting is enabled (default) or disabled	boolean	false	true
host	Set the MQTT server host name/IP	string	true
keep-alive-seconds	Set the keep alive timeout in seconds	int	false	30
max-inflight-queue	Set max count of unacknowledged messages	int	false	10
max-message-size	Set max MQTT message size in bytes	int	false	8092
merge	Whether the connector should allow multiple upstreams	boolean	false	false
password	Set the password to connect to the server	string	false
port	Set the MQTT server port. Default to 8883 if ssl is enabled, or 1883 without ssl	int	false
qos	Set the QoS level when subscribing to the topic or when sending a message	int	false	0
reconnect-interval-seconds	Set the reconnect interval in seconds	int	false	1
server-name	Set the SNI server name	string	false
ssl	Set whether SSL/TLS is enabled	boolean	false	false
ssl.keystore.location	Set the keystore location. In case of pem type this is the server ca cert path	string	false
ssl.keystore.password	Set the keystore password. In case of pem type this is the key path	string	false
ssl.keystore.type	Set the keystore type [pkcs12, jks, pem]	string	false	pkcs12
ssl.truststore.location	Set the truststore location. In case of pem type this is the client cert path	string	false
ssl.truststore.password	Set the truststore password. In case of pem type this is not necessary	string	false
ssl.truststore.type	Set the truststore type [pkcs12, jks, pem]	string	false	pkcs12
topic	Set the MQTT topic. If not set, the channel name is used	string	false
trust-all	Set whether all server certificates should be trusted	boolean	false	false
unsubscribe-on-disconnection	This flag restore the old behavior to unsubscribe from the broken on disconnection	boolean	false	false
username	Set the username to connect to the server	string	false
will-flag	Set if will information are provided on connection	boolean	false	false
will-qos	Set the QoS level for the will message	int	false	0
will-retain	Set if the will message must be retained	boolean	false	false

The MQTT connector is based on the Vert.x MQTT client. So you can pass any attribute supported by this client.

Important

A single instance of MqttClient and a single connection is used for each host / port / server-name / client-id. This client is reused for both the inbound and outbound connectors.