# Javafx Midi Device Integration

> Connect JavaFX to javax.sound.midi devices, sequencers, and receivers with safe FX-thread bridging.

- Skill: `johannesrabauer/javafx-midi-device-integration` (Agent Skill)
- Install (CLI): `npx skillmds@latest add johannesrabauer/javafx-midi-device-integration`
- Raw SKILL.md: https://api.skillmd.com/api/skills/johannesrabauer/javafx-midi-device-integration/raw
- Safety review: pending
- Works with: Claude Code, Claude.ai, OpenAI Codex
- Category: Integrations & APIs
- Author: JohannesRabauer (https://skillmd.com/u/johannesrabauer)
- Updated: 2026-09-22
- Page: https://skillmd.com/skills/johannesrabauer/javafx-midi-device-integration

---


# 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

```java
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()));
    }
}
```

```java
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.