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Core MIDI Service Provider Interface (SPI) for Java 1.7 and above on OS X, safe to load and interact with on any platform. (The SPI will simply not try to provide devices on platforms where they are not needed.)

Derek created CoreMidi4J as to our knowledge there is currently no Mac Java MIDI implementation under active development that properly supports sending System Exclusive messages, which still have not been fixed in the Java core distribution.

In collaboration with James, we added support for hot-swapping MIDI devices (the standard JAVA MIDI implementation will only recognize devices which were already connected when Java started), and proper support for inbound and outbound MIDI event timestamps, which can extend over network MIDI sessions thanks to CoreMIDI’s support for them.

Hopefully one day third-party SPIs like CoreMidi4J will not be required, but until then we are making this available.

For years we both used MMJ, but that appears to longer be under development and it does not work with later Java Runtimes. After looking around for a replacement, we decided it was necessary to create our own “lightweight” SPI, which Derek accomplished in 2015, and that we would make it publicly available for others to contribute to.

CoreMidi4J has been heavily used in some of our own projects for several years, and after resolving the last known outstanding issue we labeled it version 1.0. Over the next few years an occasional issue was discovered and fixed, or a new feature was thought up and added, leading to a new release. Feedback on any new problems or issues is always welcome.


The recommended approach for use as a library is to embed CoreMidi4J in your project and have its native code loaded automatically when on the OS X platform, so that end users do not need to worry about installing anything.

It is also still possible to download and install CoreMidi4J separately, to use it with applications that did not embed it (or if your own project does not use the Maven dependency-management ecosystem).


Using CoreMidi4J

🎹 New to Jave MIDI? CoreMidi4J is designed to be transparently compatible with the standard Java MIDI API, so we don’t provide examples or explanations of how to use that. Oracle offers a tutorial and API documentation.

Once installed, if all you want to do is use the enhanced MIDI devices provided by CoreMidi4J, all you have to do is use the normal Java MIDI API, but choose CoreMidi4J’s device implementations instead of the ones provided by the native MIDI SPI. You will be able to identify them because their names will begin with CoreMidi4J -. These devices will:

  • properly support System Exclusive messages,
  • provide, translate, and respect CoreMidi timestamps on MIDI events, and
  • the list of devices available will correctly update even if you connect or detach devices after Java is already running.

If you are using an application written by someone else, and are not making any changes to it, then this is the best you can do; you will need to remember to choose the right version of each MIDI device that you want to use.

If you are writing your own program, or willing to change the source code of the program you are using, you can make things even easier by filtering out the broken MIDI devices, and only showing the ones that work:

Filtering Out Broken MIDI Devices

If your application runs on Macs as well as other platforms, you can ensure that your users only ever see MIDI devices whose implementations work properly, by using the getMidiDeviceInfo() method provided by instead of the one in javax.sound.midi.MidiSystem. The CoreMidi4J version works on any platform. If you call it on anything but a Mac, it simply gives you the same result you would get from the standard method. On the Mac, it filters out any devices which have broken SysEx implementations, and returns the CoreMidi4J versions instead.

So to give your users the best experience possible, simply embed CoreMidi4J, and use its implementation of getMidiDeviceInfo() wherever you would otherwise have used the standard one, and your users will always only see working MIDI devices.

Watching for MIDI Device Changes

If you would like to be able to automatically update your user interface when the user connects, disconnects, or powers on/off a MIDI device, you can call addNotificationListener(listener) (also provided by the CoreMidiDeviceProvider class). This will call register a listener method to be called whenever such changes to the MIDI environment occur.

NOTE: If you use addNotificationListener on a non-macOS system, it needs to periodically scan the MIDI environment on a background thread. We have learned that the version of getMidiDeviceInfo in javax.sound.MidiSystem is not thread-safe, and if more than one thread uses it simultaneously, it will return invalid devices which throw exceptions when they are used. Because of that, you should only use the version of getMidiDeviceInfo provided by CoreMidiDeviceProvider, which uses synchronization to avoid this problem. Even if you are not using addNotificationListener, our version of the method is safer if you are using multiple threads for your own purposes.

For more details, you can consult the CoreMidi4J API documentation or even the source code, or simply keep reading.

Here is an example of what running the Example class (listed below) on a Mac, with CoreMidi4J in the classpath, produces. Notice that other than the sequencer and synthesizer, the only MIDI devices returned are the inputs and outputs offered by CoreMidi4J:

java -cp coremidi4j-1.1.jar:. Example
Working MIDI Devices:
  CoreMIDI4J - Bus 1
  CoreMIDI4J - Network
  CoreMIDI4J - Live Port
  CoreMIDI4J - User Port
  CoreMIDI4J - Traktor Virtual Output
  CoreMIDI4J - Bus 1
  CoreMIDI4J - Network
  CoreMIDI4J - Live Port
  CoreMIDI4J - User Port
  Real Time Sequencer
CoreMIDI4J native library is running.
Watching for MIDI environment changes for thirty seconds.
The MIDI environment has changed.
The MIDI environment has changed.

During the thirty seconds the code was running, a MIDI device was plugged in and later unplugged, demonstrating the fact that CoreMidi4J can adapt to changes in the MIDI environment, and notify the host application about them.

Sample Code

This class shows an example of how to ask CoreMidi4J for a list of only properly-working MIDI devices (filtering out the broken ones provided by the standard Mac OS X MIDI implementation). It also shows how to check whether the native library is available (which will only be true when you are running on a Mac), and how to ask to be notified whenever there is a change in the MIDI environment (in other words, a new device has become available, or an existing device has been removed, which works on any platform starting with CoreMidi4J version 1.4):

import javax.sound.midi.MidiDevice;

public class Example {

    public static boolean isCoreMidiLoaded() throws CoreMidiException {
        return CoreMidiDeviceProvider.isLibraryLoaded();

    public static void watchForMidiChanges() throws CoreMidiException {
        CoreMidiDeviceProvider.addNotificationListener(new CoreMidiNotification() {
                public void midiSystemUpdated() {
                    System.out.println("The MIDI environment has changed.");

    public static void main(String[] args) throws Exception {
        System.out.println("Working MIDI Devices:");
        for (javax.sound.midi.MidiDevice.Info device : CoreMidiDeviceProvider.getMidiDeviceInfo()) {
            System.out.println("  " + device);

        if (Example.isCoreMidiLoaded()) {
            System.out.println("CoreMIDI4J native library is running.");
        } else {
            System.out.println("CoreMIDI4J native library is not available.");

        System.out.println("Watching for MIDI environment changes for thirty seconds.");

Embedding CoreMidi4J

If you want your project's users to be able to rely on a correct MIDI implementation on Mac OS X without having to install anything, you can embed CoreMidi4J and thereby make it automatically available. Releases are available through Maven Central. Maven Central

It is safe to embed CoreMidi4J in cross-platform Java projects; the native library will be loaded only when needed, on Mac OS X, and the Java library will remain inactive on other platforms: it will not attempt to provide any MIDI devices, and its implementation of getMidiDeviceInfo() will simply delegate to the standard one. This means that calling our version of getMidiDeviceInfo() will always give you the correct list of devices to use on any platform.

Starting with CoreMidi4J version 1.4, you can even request to be notified of MIDI environment changes on any platform. If you are not on a Mac (where the underlying CoreMIDI library provides this service), CoreMidi4J will create a daemon thread which periodically scans the MIDI environment so that it can generate these notifications itself.

If you are building a project with code like the example above, you will need to configure CoreMidi4J as a dependency of your project. This will also enable build tools like Maven and Leiningen to build a consolidated Jar containing your own classes as well as those of CoreMidi4J, and any other libraries you depend on.

Click on the Maven Central link above, then the version you want to use, to see the configuration snippets you can use to add that version of CoreMidi4J as a dependency of your project in Maven, Gradle, Leiningen, or your build tool of choice.

Standalone CoreMidi4J

If you want to use CoreMidi4J with another Java program that does not embed it, or in a project of your own that does not use the Maven dependency management approach, you can download the standalone jar from the releases page. jar

Then simply place the CoreMidi4J jar on the classpath when that program compiles and runs, and CoreMidi4J's devices will be available to it.

Building CoreMidi4J

In order to build CoreMidi4J from source, in addition to cloning this repository, you will need to install Apple’s Xcode and Apache Maven. (We recommend using Homebrew to install Maven: once you have followed Homebrew’s own install instructions, simply run brew install maven to install Maven.)

Of course you will also need a Java development environment. Even though CoreMidi4J still can be used as far back as JDK 1.7, you need at least JDK 1.8 to build it.

Once you have Xcode and Maven, to build CoreMidi4J cd into the directory containing the Maven project specification pom.xml (you will find it in the CoreMidi4J subdirectory of your clone of this repository), and use normal Maven build commands. To build the standalone jar, for example,

cd CoreMidi4J/CoreMidi4J
mvn package

That will compile the Java classes, generate the JNI headers, compile the native library, and build the standalone jar file which embeds everything needed at runtime, using the standard Maven location and naming convention of target/coremidi4j-{version}.jar (it also builds the source and javadoc jars needed for deployment to Maven Central).

Device Names

In release 1.1 we changed the way that device names are reported to Java in order to accommodate situations where people have several of the same device attached to their system (see the Issue 21 discussion for details).

Previously, we would simply return the CoreMIDI “Endpoint” name as the device name. The problem with this is that the endpoint name for all identical devices would be the same, and there is no way for the user to edit these “Endpoint” names to distinguish between their devices.

Now, we instead return the CoreMIDI “Device” name associated with the endpoint as the Java MIDI device name. This device name can be edited by the user as described below to distinguish between their devices of the same type. And for devices that have multiple endpoints associated with them, for example a controller with different kinds of ports, we combine both the editable Device name followed by the non-editable Endpoint name.

To provide an example: the Ableton Push 2 controller has two output ports, Live Port and User Port. Under previous releases of CoreMidi4J, these would show up in Java named simply Live Port and User Port, and there was no way to change their names. In release 1.1 and later they show up as Ableton Push 2 Live Port and Ableton Push 2 User Port and the “Ableton Push 2” name can be changed to whatever you want using Audio Midi Setup as described below.

🔧 This means that if you update your application which embeds CoreMidi4J to use a current release and you were previously using release 1.0 or earlier, you may need to warn your users that their device names may have changed (if the Device and EndPoint names of any of their devices different, or for any device that has multiple Entities/Endpoints), so they need to check and update their saved configuration settings appropriately.

If you need even more details about the device, the CoreMidiDeviceInfo class returned by CoreMidi4J to describe its devices has additional properties which provide access to CoreMIDI-specific device attributes. When you know you are dealing with a MidiDevice.Info object returned by CoreMidi4J, you can cast it into a CoreMidiDeviceInfo object and access this additional information.

Editing Device Names

Users can change the device names associated with their MIDI devices using Apple’s Audio Midi Setup utility (found in the Utilities subfolder within your main Applications folder, unless you have moved it). Once the utility is launched, switch to the MIDI Studio window (using the Window menu to open it if needed):

Audio MIDI Setup

To rename the very-generic “USB MIDI Device” shown at the bottom right of this example MIDI Studio window, you could either double-click on it, or click once to select it and then click the Information button in the toolbar. That opens a Properties window where the device name can be edited:

Editing Device Name

When editing a device name like this, as soon as you click the Apply button in the Properties window, CoreMIDI4J will report a MIDI environment change event, and will use the newly assigned device name when reporting the connected MIDI devices.


Core MIDI Service provider Interace (SPI) for Java 1.7 and above on OS X




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