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Usage example

← Back to README

The example below (adapted from src/test/java/.../MqttTestMain.java) wires up a Digital Twin that generates test signals and streams all of it to PlotJuggler over MQTT, using a base topic and one dedicated topic per property/event:

public class MqttExample {

    private static final String STATE_CHANNEL = "dt-state";

    public static void main(String[] args) throws Exception {

        // 1. A Digital Twin needs a ShadowingFunction to mirror Physical Adapter data into its state
        DigitalTwin digitalTwin = new DigitalTwin("plotjuggler-mqtt-digital-twin", new DefaultShadowingFunction());

        // 2. Attach any Physical Adapter - here, the test fixture that generates sine/cosine x/y/z
        //    properties plus rotating "message"/"alarm" events (src/test/.../utils/SignalGeneratorPhysicalAdapter.java)
        digitalTwin.addPhysicalAdapter(
                new SignalGeneratorPhysicalAdapter("test-pa", new SignalGeneratorPhysicalAdapterConfiguration(200, 1000, 0.1))
        );

        // 3. Configure the MQTT connection: broker target, plus an optional topic prefix
        MqttConnectionConfiguration mqttConnectionConfiguration = new MqttConnectionConfiguration("127.0.0.1", 1883);
        mqttConnectionConfiguration.setBaseTopic("test/wldt-da");

        // 4. Build the adapter configuration: JSON format, one whole-state channel, one channel per
        //    property/event - each becomes its own MQTT topic under "test/wldt-da/..."
        PlotJugglerDigitalAdapterConfiguration configuration = PlotJugglerDigitalAdapterConfiguration
                .builder(mqttConnectionConfiguration, PlotJugglerMessageFormat.JSON)
                .withStateChannel(STATE_CHANNEL)
                .addPropertyChannel(SignalGeneratorPhysicalAdapter.X_PROPERTY_KEY, "x")
                .addPropertyChannel(SignalGeneratorPhysicalAdapter.Y_PROPERTY_KEY, "y")
                .addPropertyChannel(SignalGeneratorPhysicalAdapter.Z_PROPERTY_KEY, "z")
                .addEventChannel(SignalGeneratorPhysicalAdapter.MESSAGE_EVENT_KEY, "event_message")
                .addEventChannel(SignalGeneratorPhysicalAdapter.ALARM_EVENT_KEY, "event_alarm")
                .build();

        // 5. Attach the PlotJuggler Digital Adapter and start everything
        digitalTwin.addDigitalAdapter(new PlotJugglerDigitalAdapter("plotjuggler-mqtt-da", configuration));

        DigitalTwinEngine digitalTwinEngine = new DigitalTwinEngine();
        digitalTwinEngine.addDigitalTwin(digitalTwin);
        digitalTwinEngine.startAll();
    }
}

Trying it out

There are no automated tests in this project: every connection is meant to be exercised by hand against real, already running infrastructure (a real PlotJuggler instance for UDP/WebSocket, a real external MQTT broker for MQTT). src/test/java/.../it/wldt/adapter/plotjuggler/digital/ contains ready-to-run entry points, all sharing the same SignalGeneratorPhysicalAdapter/DefaultShadowingFunction test fixtures and each exercising a different scenario:

  • MqttTestMain - MQTT, default target 127.0.0.1:1883, override with -Dmqtt.broker.host=... -Dmqtt.broker.port=.... Uses baseTopic/isSingleTopic to demonstrate the topic-layout options (see protocols.md).
  • UdpTestMain - UDP, default target 127.0.0.1:9870, override with -Dplotjuggler.udp.host=... -Dplotjuggler.udp.port=.... Has the other formats (BSON/CBOR/MessagePack) left commented next to the active JSON one, as a quick reference for swapping formats.
  • UdpCustomFunctionTestMain - same UDP target/overrides as UdpTestMain, but demonstrates custom event payload functions (see channels.md): the "message"/"alarm" events are mapped to plain integers (a message-list index, and 0/1) instead of forwarded as-is, since PlotJuggler plots numeric series and a raw string/boolean value isn't directly plottable.
  • WebSocketTestMain - WebSocket, default target 127.0.0.1:9871, override with -Dplotjuggler.websocket.host=... -Dplotjuggler.websocket.port=....

Each is a plain class with a main(String[] args): run it directly from your IDE (passing any -D... overrides as VM options), then watch the data arrive live in PlotJuggler (or with an external tool such as mosquitto_sub for the MQTT case) to confirm end-to-end delivery.