AddOptionalSupportToKVC.java

package gardur.app;

import java.util.Optional;

import com.webobjects.foundation.NSKeyValueCoding;

import net.bytebuddy.ByteBuddy;
import net.bytebuddy.agent.ByteBuddyAgent;
import net.bytebuddy.asm.Advice;
import net.bytebuddy.dynamic.loading.ClassReloadingStrategy;
import net.bytebuddy.matcher.ElementMatchers;

public class AddOptionalSupportToKVC {

    public static void register() {
        ByteBuddyAgent.install();

        new ByteBuddy()
                .redefine( NSKeyValueCoding.DefaultImplementation.class )
                .visit( Advice.to( KVCAdvisor.class )
                        .on( ElementMatchers.named( "valueForKey" ) ) )
                .make()
                .load(
                        NSKeyValueCoding.DefaultImplementation.class.getClassLoader(),
                        ClassReloadingStrategy.fromInstalledAgent() );

    }

    public static class KVCAdvisor {
        @Advice.OnMethodExit
        static void exit( @Advice.Return( readOnly = false ) Object returnValue ) throws Exception {
            if( returnValue instanceof Optional ) {
                if( ((Optional)returnValue).isPresent() ) {
                    returnValue = ((Optional)returnValue).get();
                }
                else {
                    returnValue = null;
                }
            }
        }
    }

    public static class TestOptionalSupport {
        public static void main( String argv[] ) {
            AddOptionalSupportToKVC.register();
            Object emptyResult = NSKeyValueCoding.DefaultImplementation.valueForKey( new TestOptionalSupport(), "emptyOptional" );
            Object presentResult = NSKeyValueCoding.DefaultImplementation.valueForKey( new TestOptionalSupport(), "presentOptional" );
            System.out.println( "emptyResult: " + emptyResult ); // This is null
            System.out.println( "presentResult: " + presentResult ); // This is "I'm not empty!"
        }
        
        public Optional<String> emptyOptional() {
            return Optional.empty();
        }
        
        public Optional<String> presentOptional() {
            return Optional.of( "I'm not empty!" );
        }
    }
}