File associations

fileAssociations registers file types for your app, so users can open those files with it (double click, "Open with...").

Maven

<fileAssociations>
    <fileAssociation>
        <mimeType>application/x-foo</mimeType>
        <extension>foo</extension>
        <description>Foo document</description>
    </fileAssociation>
</fileAssociations>

Gradle

import io.github.javapackager.model.FileAssociation

javapackager {
    fileAssociations = [
        new FileAssociation(mimeType: 'application/x-foo', extension: 'foo', description: 'Foo document')
    ]
}

Field	Description
extension	File extension, without the dot.
mimeType	MIME type of the files.
description	Description of the file type shown to users.

The app receives the file to open as a command-line argument.

Per platform

Platform	What's registered
GNU/Linux	The MIME types in the app's desktop entry (DEB, RPM, AppImage). The DEB also installs a MIME type definition (/usr/share/mime/packages/${name}.xml) with the extension.
macOS	Document types and exported types in Info.plist, with the type identifier ${appId}.${extension}.
Windows	The Setup registers the extension and an "Open" command for the app, and removes them on uninstall.

note

The MSI doesn't register file associations yet; use the Setup if you need them.

On macOS, files are opened through Apple events: Java apps get them with java.awt.Desktop.setOpenFileHandler, not as arguments.