processing-mqtt

MQTT library for Processing based on the Eclipse Paho project

This library bundles the Java Client library of the Eclipse Paho project and adds a thin wrapper to get a Processing like API.

Download the latest version of the library.

Or even better use the Library Manager in the Processing IDE.

Example

This example sketch connects to the public shiftr.io instance and sends a message on every keystroke. After starting the sketch you can find the client here: https://www.shiftr.io/try.

import mqtt.*;

MQTTClient client;

void setup() {
  client = new MQTTClient(this);
  client.connect("mqtt://public:public@public.cloud.shiftr.io", "processing");
}

void draw() {}

void keyPressed() {
  client.publish("/hello", "world");
}

void clientConnected() {
  println("client connected");

  client.subscribe("/hello");
}

void messageReceived(String topic, byte[] payload) {
  println("new message: " + topic + " - " + new String(payload));
}

void connectionLost() {
  println("connection lost");
}

API

Instantiate a new client by supplying the parent applet:

MQTTClient client = new MQTTClient(PApplet parent);

• The constructor expects the following method to be declared on the parent applet: void messageReceived(String topic, byte[] payload). That callback will then be invoked in the future with incoming messages.
• Additionally, the following callbacks will be detected: void clientConnected() and void connectionLost() and executed appropriately.

Alternatively you can provide your own Listener class instead of relying on global methods:

MQTTClient client = new MQTTClient(PApplet parent, Listener listener);

• You can find the interface here: https://github.com/256dpi/processing-mqtt/blob/master/src/mqtt/MQTTListener.java.

Set the will message that gets transmitted to the server in all subsequent connect commands:

void client.setWill(String topic, String payload);
void client.setWill(String topic, String payload, int qos, boolean retained);

• The QoS level and retained flag default to 0 and false respectively.

Connect to the supplied broker by parsing the URL and setting the optionally supplied client id and clean session flag:

void client.connect(String brokerURI);
void client.connect(String brokerURI, String clientId);
void client.connect(String brokerURI, String clientId, boolean cleanSession);

• A client id will be generated if needed and the clean session flag defaults to true.

Publish a message to the broker using the supplied topic and the optional payload in form of a String or byte-array. If available it will set the QoS level as well as the retained flag appropriately.

void client.publish(String topic);
void client.publish(String topic, String payload);
void client.publish(String topic, String payload, int qos, boolean retained);
void client.publish(String topic, byte[] payload);
void client.publish(String topic, byte[] payload, int qos, boolean retained);

• The QoS level and the retained flag default to 0 and false respectively.

Subscribe to the supplied topic using the optionally provided QoS level that defaults to 0:

void client.subscribe(String topic);
void client.subscribe(String topic, int qos);

Unsubscribe from the supplied topic:

void client.unsubscribe(String topic);

Disconnect from the broker:

void client.disconnect();

Notes

• If you're running the sketch via the Android Mode you need to set the INTERNET permission in Android > Sketch Permissions.