macOS fileAssociations

<dict>
    <key>CFBundleDocumentTypes</key>
    <array>
        <dict>
            <key>CFBundleTypeExtensions</key>
            <array>
                <string>jar</string>
            </array>
            <key>CFBundleTypeName</key>
            <string>Java JAR file</string>
            <key>CFBundleTypeRole</key>
            <string>Viewer</string>
            <key>LSHandlerRank</key>
            <string>Default</string>
        </dict>
    </array>
</dict>

INFOPLIST_KEY_LSUIElement = YES
INFOPLIST_KEY_NSPrincipalClass = NSApplication

<?xml version="1.0" encoding="UTF-8"?>
<document type="com.apple.InterfaceBuilder3.Cocoa.XIB" version="3.0" toolsVersion="23727" targetRuntime="MacOSX.Cocoa" propertyAccessControl="none" useAutolayout="YES" customObjectInstantitationMethod="direct">
    <dependencies>
        <plugIn identifier="com.apple.InterfaceBuilder.CocoaPlugin" version="23727"/>
    </dependencies>
    <objects>
        <customObject id="-2" userLabel="File's Owner" customClass="NSApplication">
            <connections>
                <outlet property="delegate" destination="Voe-Tx-rLC" id="jth-LA-gLs"/>
            </connections>
        </customObject>
        <customObject id="-1" userLabel="First Responder" customClass="FirstResponder"/>
        <customObject id="-3" userLabel="Application" customClass="NSObject"/>
        <customObject id="Voe-Tx-rLC" customClass="AppDelegate"/>
    </objects>
</document>

#import <Cocoa/Cocoa.h>

int main(int argc, const char * argv[]) {
    @autoreleasepool {
    }
    return NSApplicationMain(argc, argv);
}

#import <Cocoa/Cocoa.h>

@interface AppDelegate : NSObject <NSApplicationDelegate>
@end

#import "AppDelegate.h"

@interface AppDelegate ()

@end

@implementation AppDelegate

- (void)applicationDidFinishLaunching:(NSNotification *)aNotification {
    // Insert code here to initialize your application
}

- (void)applicationWillTerminate:(NSNotification *)aNotification {
    // Insert code here to tear down your application
}

- (BOOL)applicationSupportsSecureRestorableState:(NSApplication *)app {
    return YES;
}

- (BOOL)application:(NSApplication *)sender openFile:(NSString *)filename {
    NSLog(@"[DEBUG] openFile: called with file: %@", filename);
    return YES;
}

- (void)application:(NSApplication *)sender openFiles:(NSArray<NSString *> *)filenames {
    NSLog(@"[DEBUG] openFiles: called with files: %@", filenames);
}


/// If your delegate implements this method, 
///  AppKit does not call the application:openFile: or application:openFiles: methods.
//- (void)application:(NSApplication *)application openURLs:(NSArray<NSURL *> *)urls {
//    NSLog(@"[DEBUG] openURLs: called with URLs: %@", urls);
//}

@end

#import "AppDelegate.h"
#import <Cocoa/Cocoa.h>

int main(int argc, const char *argv[]) {
    @autoreleasepool {
        NSApplication *app = [NSApplication sharedApplication];
        AppDelegate *appDelegate = [[AppDelegate alloc] init];
        [app setDelegate:appDelegate];
        [app run];
    }
    return 0;
}