OSXAdapter.java

/*

File: OSXAdapter.java

Abstract: Hooks existing preferences/about/quit functionality from an
    existing Java app into handlers for the Mac OS X application menu.
    Uses a Proxy object to dynamically implement the 
    com.apple.eawt.ApplicationListener interface and register it with the
    com.apple.eawt.Application object.  This allows the complete project
    to be both built and run on any platform without any stubs or 
    placeholders. Useful for developers looking to implement Mac OS X 
    features while supporting multiple platforms with minimal impact.
			
Version: 2.0

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*/

package com.apple;
import java.lang.reflect.*;


public class OSXAdapter implements InvocationHandler {

    protected Object targetObject;
    protected Method targetMethod;
    protected String proxySignature;

    static Object macOSXApplication;

    // Pass this method an Object and Method equipped to perform application shutdown logic
    // The method passed should return a boolean stating whether or not the quit should occur
    public static void setQuitHandler(Object target, Method quitHandler) {
        setHandler(new OSXAdapter("handleQuit", target, quitHandler));
    }

    // Pass this method an Object and Method equipped to display application info
    // They will be called when the About menu item is selected from the application menu
    public static void setAboutHandler(Object target, Method aboutHandler) {
        boolean enableAboutMenu = (target != null && aboutHandler != null);
        if (enableAboutMenu) {
            setHandler(new OSXAdapter("handleAbout", target, aboutHandler));
        }
        // If we're setting a handler, enable the About menu item by calling
        // com.apple.eawt.Application reflectively
        try {
            Method enableAboutMethod = macOSXApplication.getClass().getDeclaredMethod("setEnabledAboutMenu", new Class[] { boolean.class });
            enableAboutMethod.invoke(macOSXApplication, new Object[] { Boolean.valueOf(enableAboutMenu) });
        } catch (Exception ex) {
            System.err.println("OSXAdapter could not access the About Menu");
            ex.printStackTrace();
        }
    }

    // Pass this method an Object and a Method equipped to display application options
    // They will be called when the Preferences menu item is selected from the application menu
    public static void setPreferencesHandler(Object target, Method prefsHandler) {
        boolean enablePrefsMenu = (target != null && prefsHandler != null);
        if (enablePrefsMenu) {
            setHandler(new OSXAdapter("handlePreferences", target, prefsHandler));
        }
        // If we're setting a handler, enable the Preferences menu item by calling
        // com.apple.eawt.Application reflectively
        try {
            Method enablePrefsMethod = macOSXApplication.getClass().getDeclaredMethod("setEnabledPreferencesMenu", new Class[] { boolean.class });
            enablePrefsMethod.invoke(macOSXApplication, new Object[] { Boolean.valueOf(enablePrefsMenu) });
        } catch (Exception ex) {
            System.err.println("OSXAdapter could not access the About Menu");
            ex.printStackTrace();
        }
    }

    // Pass this method an Object and a Method equipped to handle document events from the Finder
    // Documents are registered with the Finder via the CFBundleDocumentTypes dictionary in the 
    // application bundle's Info.plist
    public static void setFileHandler(Object target, Method fileHandler) {
        setHandler(new OSXAdapter("handleOpenFile", target, fileHandler) {
            // Override OSXAdapter.callTarget to send information on the
            // file to be opened
            public boolean callTarget(Object appleEvent) {
                if (appleEvent != null) {
                    try {
                        Method getFilenameMethod = appleEvent.getClass().getDeclaredMethod("getFilename", (Class[])null);
                        String filename = (String) getFilenameMethod.invoke(appleEvent, (Object[])null);
                        this.targetMethod.invoke(this.targetObject, new Object[] { filename });
                    } catch (Exception ex) {

                    }
                }
                return true;
            }
        });
    }

    // setHandler creates a Proxy object from the passed OSXAdapter and adds it as an ApplicationListener
    public static void setHandler(OSXAdapter adapter) {
        try {
            Class<?> applicationClass = Class.forName("com.apple.eawt.Application");
            if (macOSXApplication == null) {
                macOSXApplication = applicationClass.getConstructor((Class[])null).newInstance((Object[])null);
            }
            Class<?> applicationListenerClass = Class.forName("com.apple.eawt.ApplicationListener");
            Method addListenerMethod = applicationClass.getDeclaredMethod("addApplicationListener", new Class[] { applicationListenerClass });
            // Create a proxy object around this handler that can be reflectively added as an Apple ApplicationListener
            Object osxAdapterProxy = Proxy.newProxyInstance(OSXAdapter.class.getClassLoader(), new Class[] { applicationListenerClass }, adapter);
            addListenerMethod.invoke(macOSXApplication, new Object[] { osxAdapterProxy });
        } catch (ClassNotFoundException cnfe) {
            System.err.println("This version of Mac OS X does not support the Apple EAWT.  ApplicationEvent handling has been disabled (" + cnfe + ")");
        } catch (Exception ex) {  // Likely a NoSuchMethodException or an IllegalAccessException loading/invoking eawt.Application methods
            System.err.println("Mac OS X Adapter could not talk to EAWT:");
            ex.printStackTrace();
        }
    }

    // Each OSXAdapter has the name of the EAWT method it intends to listen for (handleAbout, for example),
    // the Object that will ultimately perform the task, and the Method to be called on that Object
    protected OSXAdapter(String proxySignature, Object target, Method handler) {
        this.proxySignature = proxySignature;
        this.targetObject = target;
        this.targetMethod = handler;
    }

    // Override this method to perform any operations on the event 
    // that comes with the various callbacks
    // See setFileHandler above for an example
    public boolean callTarget(Object appleEvent) throws InvocationTargetException, IllegalAccessException {
        Object result = targetMethod.invoke(targetObject, (Object[])null);
        if (result == null) {
            return true;
        }
        return Boolean.valueOf(result.toString()).booleanValue();
    }

    // InvocationHandler implementation
    // This is the entry point for our proxy object; it is called every time an ApplicationListener method is invoked
    public Object invoke (Object proxy, Method method, Object[] args) throws Throwable {
        if (isCorrectMethod(method, args)) {
            boolean handled = callTarget(args[0]);
            setApplicationEventHandled(args[0], handled);
        }
        // All of the ApplicationListener methods are void; return null regardless of what happens
        return null;
    }

    // Compare the method that was called to the intended method when the OSXAdapter instance was created
    // (e.g. handleAbout, handleQuit, handleOpenFile, etc.)
    protected boolean isCorrectMethod(Method method, Object[] args) {
        return (targetMethod != null && proxySignature.equals(method.getName()) && args.length == 1);
    }

    // It is important to mark the ApplicationEvent as handled and cancel the default behavior
    // This method checks for a boolean result from the proxy method and sets the event accordingly
    protected void setApplicationEventHandled(Object event, boolean handled) {
        if (event != null) {
            try {
                Method setHandledMethod = event.getClass().getDeclaredMethod("setHandled", new Class[] { boolean.class });
                // If the target method returns a boolean, use that as a hint
                setHandledMethod.invoke(event, new Object[] { Boolean.valueOf(handled) });
            } catch (Exception ex) {
                System.err.println("OSXAdapter was unable to handle an ApplicationEvent: " + event);
                ex.printStackTrace();
            }
        }
    }
}