Client API. The Codename One framework your app is built on: this runs on the device, not in a backend.

public final class MqttClient

Object
MqttClient

An MQTT 3.1.1 client for QoS 0 and QoS 1.

Threading

Like the rest of the framework the client is single threaded: call it on the EDT, and every MqttListener / MqttMessageListener callback arrives there. Transport threads only post to the EDT, so the client itself holds no locks. Writes happen on the calling thread.

Delivery

A QoS 1 publish stays in flight until its PUBACK and is sent again, with the DUP flag, after a reconnect; with a clean session the in flight list is dropped when connecting. A QoS 1 publish made while disconnected is queued and sent after the next successful connect. QoS 0 needs a connection. An incoming QoS 1 message is acknowledged before it is delivered.

Keep alive

A small daemon thread ticks once a second and posts the check to the EDT. A PINGREQ goes out when nothing was sent for the keep alive interval; when no PINGRESP arrives within one and a half intervals the connection is declared lost. The same tick enforces the connect timeout.

Subscriptions

A subscription made with a listener routes matching messages to it only; a message no such subscription claims goes to the MqttListener. The client does not re-subscribe on reconnect: do it from MqttListener.connected() (a broker keeps the subscriptions of a persistent session, cleanSession(false)).

Constructors

public MqttClient() Creates a disconnected client.

Methods

`public void connect(MqttOptions options, MqttListener listener)`	Opens a connection and sends CONNECT.
`public boolean isConnected()`	Whether the broker has accepted the connection and it is still up.
`public int getInFlightCount()`	The number of QoS 1 publishes not yet acknowledged, queued ones included.
`public void publish(String topic, byte[] payload, int qos, boolean retain)`	Publishes a message.
`public void subscribe(String topicFilter, int qos)`	Subscribes; matching messages go to the `MqttListener`.
`public void subscribe(String topicFilter, int qos, MqttMessageListener messageListener)`	Subscribes and routes matching messages to a listener of their own.
`public void unsubscribe(String topicFilter)`	Removes a subscription.
`public void disconnect()`	Sends DISCONNECT and closes the connection.

Inherited methods

From Object

equals, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait, clone, finalize

Constructor details

MqttClient

public MqttClient()

Creates a disconnected client.

Method details

connect

public void connect(MqttOptions options, MqttListener listener)

Opens a connection and sends CONNECT. Returns at once; the outcome arrives as MqttListener.connected() or MqttListener.connectionLost(String).

Throws

IllegalStateException when already connected or connecting, IllegalArgumentException for an unsupported URI

Parameters

options MqttOptions: broker and session settings
listener MqttListener: receives the callbacks

isConnected

public boolean isConnected()

Whether the broker has accepted the connection and it is still up.

getInFlightCount

public int getInFlightCount()

The number of QoS 1 publishes not yet acknowledged, queued ones included.

publish

public void publish(String topic, byte[] payload, int qos, boolean retain)

Publishes a message.

Parameters

topic String: the topic name, without wildcards
payload byte[]: the message body
qos int: 0 (needs a connection) or 1 (queued until connected)
retain boolean: ask the broker to retain the message

public void subscribe(String topicFilter, int qos)

Subscribes; matching messages go to the MqttListener.

Parameters

topicFilter String: the filter, + and # allowed
qos int: the maximum QoS wanted, 0 or 1

public void subscribe(String topicFilter, int qos, MqttMessageListener messageListener)

Subscribes and routes matching messages to a listener of their own.

Parameters

topicFilter String: the filter, + and # allowed
qos int: the maximum QoS wanted, 0 or 1
messageListener MqttMessageListener: receives the matches; null means the MqttListener

unsubscribe

public void unsubscribe(String topicFilter)

Removes a subscription.

Parameters

topicFilter String: the filter given to subscribe

disconnect

public void disconnect()

Sends DISCONNECT and closes the connection. No connectionLost follows. QoS 1 publishes still unacknowledged stay queued for the next connect.