Example Mac OSX Magnify and Rotate gestures in a Swing app that will compile on all platform but only work on Mac (help with other platforms welcome)

Indigesturing.java

package xyz.arwhite.swing;

import java.awt.Dimension;
import java.awt.event.MouseAdapter;
import java.awt.event.MouseEvent;
import java.awt.event.MouseWheelEvent;
import java.lang.reflect.Constructor;
import java.lang.reflect.InvocationHandler;
import java.lang.reflect.Method;
import java.lang.reflect.Proxy;

import javax.swing.JFrame;
import javax.swing.JPanel;
import javax.swing.SwingUtilities;
import javax.swing.WindowConstants;

/*
 * To make this work ensure on jdk17.02+2 onwards
 * Compile with -XDignore.symbol.file --add-exports java.desktop/com.apple.eawt.event=ALL-UNNAMED 
 * Run with --add-opens java.desktop/com.apple.eawt.event=ALL-UNNAMED 
 * 
 * This will compile and run on platforms other than osx as it uses reflection to reach the
 * osx specific classes.
 */

@SuppressWarnings("serial")
public class Indigesturing extends JFrame {

	public class MagnifyHandler implements InvocationHandler {

		public Object invoke(Object proxy, Method method, Object[] args) {
			// method.getName() should always return "magnify" as that's all we subscribed to
			// production code may wish to double check this.
			try {
				for(Object o: args) {
					Object mag = o.getClass()
							.getMethod("getMagnification")
							.invoke(o);

					// mag.getClass() should always return java.lang.Double
					// production code may wish to check double this (no pun intended)
					System.out.println("Magnify: "+mag);
				}
			} catch (Exception e) {
				e.printStackTrace();
			}
			return null;
		}
	}

	public class RotateHandler implements InvocationHandler {

		public Object invoke(Object proxy, Method method, Object[] args) {
			// method.getName() should always return "rotate" as that's all we subscribed to
			// production code may wish to double check this.
			try {
				for(Object o: args) {
					Object rot = o.getClass()
							.getMethod("getRotation")
							.invoke(o);

					// mag.getClass() should always return java.lang.Double
					// production code may wish to check double this (no pun intended)
					System.out.println("Rotate: "+rot);
				}
			} catch (Exception e) {
				e.printStackTrace();
			}
			return null;
		}
	}


	public Indigesturing() {
		super();
		setDefaultCloseOperation(WindowConstants.EXIT_ON_CLOSE);
		this.setPreferredSize(new Dimension(600,400));

		JPanel p = new JPanel();
		getContentPane().add(p);

		/*
		GestureUtilities.addGestureListenerTo(p, (GestureListener) new MagnificationListener() { 
			@Override 
			public void magnify(MagnificationEvent magnificationEvent) { 
				System.out.println("Magnify "+magnificationEvent.getMagnification());
			} 
			@Override 
			public void rotate(RotationEvent rotationEvent) { 
				System.out.println("Rotate: "+rotationEvent.getrotation());
			} 
		});
		 */

		// 40 odd lines of code replace 10 lines to make it cross-platform friendly
		if (System.getProperty("os.name").contains("Mac")) {
			try {
				// Run with --add-opens java.desktop/com.apple.eawt.event=ALL-UNNAMED 
				Constructor[] constructors = Class.forName("com.apple.eawt.event.GestureUtilities")
						.getDeclaredConstructors();

				Object gu=null;

				for (Constructor constructor : constructors) 
				{
					constructor.setAccessible(true);
					gu = constructor.newInstance();
					break;
				}

				Object mh = Proxy.newProxyInstance(
						Class.forName("com.apple.eawt.event.MagnificationListener").getClassLoader(),
						new Class[]{Class.forName("com.apple.eawt.event.MagnificationListener")},
						new MagnifyHandler()
						);

				gu.getClass()
				.getMethod("addGestureListenerTo", 
						Class.forName("javax.swing.JComponent"),
						Class.forName("com.apple.eawt.event.GestureListener"))
				.invoke(gu, p, mh);

				Object rh = Proxy.newProxyInstance(
						Class.forName("com.apple.eawt.event.RotationListener").getClassLoader(),
						new Class[]{Class.forName("com.apple.eawt.event.RotationListener")},
						new RotateHandler()
						);

				gu.getClass()
				.getMethod("addGestureListenerTo", 
						Class.forName("javax.swing.JComponent"),
						Class.forName("com.apple.eawt.event.GestureListener"))
				.invoke(gu, p, rh);

			}
			catch (Exception e) {
				e.printStackTrace();
			}
		}

		var ma = new MouseAdapter() {

			/*
			 * 2-finger swipe is a mouse wheel scroll
			 * modifier/ext-modifier of shift is supplied if horizontal, otherwise vertical
			 * wheelRotation is positive for up/left swipes, negative for down/right, preciseWheelRotation follows, almost always updates, even if wheelRotation 0
			 * using the touchpad appears to use some momentum algo under the covers as events can keep coming after fingers have left contact with the pad
			 * not evident how to tell when contact has been broken, rotation reduces as moment reduces
			 * 
			 * This bug is the only place I've seen that documents the shift behaviour https://bugs.openjdk.java.net/browse/JDK-8203048
			 */
			@Override
			public void mouseWheelMoved(MouseWheelEvent e) { 
				System.out.println(e); 
			}

			/*
			 * 3-finger swipe is a drag event, reported as Button1 being pressed, even if no click down has been made
			 * There is no difference between a 3-finger drag whilst clicked/pressed into the pad, and not
			 * 
			 * 2-finger click and drag, is reported as a drag event with cmd+Button3 modifiers
			 * 2-finger swipe, ie no click, is a mouse scroll event, see above
			 * 
			 * 1-finger click and drag, is a drag and reports as Button1 pressed, exactly the same as a 3-finger swipe, just no button down event before (I imagine)
			 * 
			 * Direction is always determined by the co-ordinate move. There is no concept of momentum as this event relies on the co-ordinates of the pointer.
			 */
			@Override
			public void mouseDragged(MouseEvent e) { System.out.println(e); }

		};

		p.addMouseListener(ma);
		p.addMouseMotionListener(ma);
		p.addMouseWheelListener(ma);

		pack();
		setVisible(true);

	}

	public static void main(String[] args) {

		SwingUtilities.invokeLater(new Runnable() {
			public void run() {
				new Indigesturing();
			}
		});
	}
}