javafx-midi-device-integration

name	javafx-midi-device-integration
description	Connect JavaFX to javax.sound.midi devices, sequencers, and receivers with safe FX-thread bridging.
triggers	["javafx midi","javax.sound.midi javafx","javafx sequencer midi","midi receiver javafx"]
compatibility	{"java":"17+","javafx":"21+"}
category	platform-integration
tags	["midi","java-sound","receiver","sequencer","hardware"]
metadata	{"scope":"repository","maturity":"starter"}
allowed-tools	["view","rg","apply_patch"]

JavaFX MIDI Device Integration

Use this skill when a JavaFX app must talk to javax.sound.midi: play MIDI files, open hardware devices, decode note/control events, or route MIDI activity into JavaFX UI state.

Example

import javax.sound.midi.MidiChannel;
import javax.sound.midi.MidiSystem;
import javax.sound.midi.ShortMessage;
import javax.sound.midi.Synthesizer;
import javafx.application.Platform;
import javafx.scene.control.Label;
import javafx.scene.layout.VBox;

public class MidiMonitorView extends VBox {

    private MidiChannel channel;

    public MidiMonitorView() throws Exception {
        var status = new Label("Idle");
        getChildren().add(status);

        Synthesizer synthesizer = MidiSystem.getSynthesizer();
        synthesizer.open();
        channel = synthesizer.getChannels()[0];

        ShortMessage noteOn = new ShortMessage();
        noteOn.setMessage(ShortMessage.NOTE_ON, 0, 60, 96);

        channel.noteOn(noteOn.getData1(), noteOn.getData2());
        Platform.runLater(() -> status.setText("Played note " + noteOn.getData1()));
    }
}

module com.example.app {
    requires java.desktop;
    requires javafx.controls;
}

Setup notes

• Use Synthesizer and MidiChannel for direct sound generation, Sequencer for MIDI file playback, and MidiDevice discovery when hardware routing matters.
• Treat Receiver.send(...) and other MIDI callbacks as non-FX threads; bridge UI updates with Platform.runLater(...).
• Decode ShortMessage carefully: command, channel, note/controller number, and velocity/value.

Gotchas

• NOTE_ON with velocity 0 is effectively NOTE_OFF.
• MIDI callbacks that touch the scene graph directly will break thread-safety.
• Device discovery should filter out endpoints that cannot transmit or that represent the synth or sequencer when the app is searching for external input.