Receiving messages from MQTT

The MQTT Connector connects to a MQTT broker or router, and forward the messages to the Reactive Messaging application. It maps each of them into Reactive Messaging Messages.

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 receive MQTT messages on the prices channel as follows:

1
2
3

mp.messaging.incoming.prices.connector=smallrye-mqtt # <1>
mp.messaging.incoming.prices.host=mqtt # <2>
mp.messaging.incoming.prices.port=1883 # <3>

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.

Important

Message coming from MQTT have a byte[] payload.

Then, your application receives Message<byte[]>. You can consume the payload directly:

package mqtt.inbound;

import javax.enterprise.context.ApplicationScoped;

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

@ApplicationScoped
public class MqttPriceConsumer {

    @Incoming("prices")
    public void consume(byte[] raw) {
        double price = Double.parseDouble(new String(raw));

        // process your price.
    }

}

Or, you can retrieve the Message<byte[]>:

package mqtt.inbound;

import java.util.concurrent.CompletionStage;

import javax.enterprise.context.ApplicationScoped;

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

@ApplicationScoped
public class MqttPriceMessageConsumer {

    @Incoming("prices")
    public CompletionStage<Void> consume(Message<byte[]> price) {
        // process your price.

        // Acknowledge the incoming message
        return price.ack();
    }

}

The inbound topic can use the MQTT wildcards (+ and #).

Deserialization

The MQTT Connector does not handle the deserialization and creates a Message<byte[]>.

Inbound Metadata

The MQTT connector does not provide inbound metadata.

Failure Management

If a message produced from a MQTT message is nacked, a failure strategy is applied. The MQTT connector supports 3 strategies:

fail - fail the application, no more MQTT messages will be processed. (default) The offset of the record that has not been processed correctly is not committed.
ignore - the failure is logged, but the processing continue.

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`
broadcast	Whether or not the messages should be dispatched to multiple consumers	boolean	false	`false`
buffer-size	The size buffer of incoming messages waiting to be processed	int	false	`128`
client-id	Set the client identifier	string	false
connect-timeout-seconds	Set the connect timeout (in seconds)	int	false	`60`
failure-strategy	Specify the failure strategy to apply when a message produced from a MQTT message is nacked. Values can be `fail` (default), or `ignore`	string	false	`fail`
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`
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.

Important

Using auto-clean-session=false the MQTT Connector send Subscribe requests to the broken only if a Persistent Session is not present (like on the first connection). This means that if a Session is already present (maybe for a previous run) and you add a new incoming channel, this will not be subscribed. Beware to check always the subscription present on Broker when use auto-clean-session=false.