DynamoReflectiveSerializer.java

import java.lang.reflect.*;
import java.util.*;
import java.util.function.Function;
import com.amazonaws.services.dynamodbv2.model.AttributeValue;
import lombok.*;

@SuppressWarnings( "unchecked" )
public abstract class DynamoReflectiveSerializer {

	private static final Map<Class, Function<Field, FieldAttributeValueReader>> fieldHoldersFactories = new HashMap<>();
	private static final Map<Class, Function<Object, AttributeValue>> typeHolder = new HashMap<>();
	private static final AttributeValue nullValue = new AttributeValue().withNULL( true );
	private static final Function<Field, FieldAttributeValueReader> complexObjectAttributeHolder = ComplexObjectAttributeValue::new;

	static {
		fieldHoldersFactories.put( String.class, StringAttributeValue::new );
		fieldHoldersFactories.put( int.class, IntegerAttributeValue::new );
		fieldHoldersFactories.put( Integer.class, IntegerAttributeValue::new );
		fieldHoldersFactories.put( long.class, LongAttributeValue::new );
		fieldHoldersFactories.put( Long.class, LongAttributeValue::new );
		fieldHoldersFactories.put( double.class, DoubleAttributeValue::new );
		fieldHoldersFactories.put( Double.class, DoubleAttributeValue::new );
		fieldHoldersFactories.put( boolean.class, BooleanAttributeValue::new );
		fieldHoldersFactories.put( Boolean.class, BooleanAttributeValue::new );
		fieldHoldersFactories.put( List.class, ListAttributeValue::new );
		fieldHoldersFactories.put( Map.class, MapAttributeValue::new );
	}

	static {
		typeHolder.put( String.class, o -> AttributeValue.create( o.toString() ) );
		typeHolder.put( int.class, o -> AttributeValue.create( (Integer)o ) );
		typeHolder.put( Integer.class, o -> AttributeValue.create( (Integer)o ) );
		typeHolder.put( long.class, o -> AttributeValue.create( (Long)o ) );
		typeHolder.put( Long.class, o -> AttributeValue.create( (Long)o ) );
		typeHolder.put( double.class, o -> AttributeValue.create( (Double)o ) );
		typeHolder.put( Double.class, o -> AttributeValue.create( (Double)o ) );
		typeHolder.put( boolean.class, o -> AttributeValue.create( (Boolean)o ) );
		typeHolder.put( Boolean.class, o -> AttributeValue.create( (Boolean)o ) );
	}

	public static AttributeValue serialize( Object object ) {
		if ( object == null ) return nullValue;
		return typeHolder
			.computeIfAbsent( object.getClass(), DynamoReflectiveSerializer::compile )
			.apply( object );
	}

	private static Function<Object, AttributeValue> compile( Class clazz ) {
		final List<FieldAttributeValueReader> attributes = new ArrayList<>();
		
		while ( !Object.class.equals( clazz ) ) {
			for ( Field field : clazz.getDeclaredFields() ) {
				if ( Modifier.isStatic( field.getModifiers() ) )
					continue;
				field.setAccessible( true );
				val holder = fieldHoldersFactories.getOrDefault( field.getType(), complexObjectAttributeHolder );
				attributes.add( holder.apply( field ) );
			}

			clazz = clazz.getSuperclass();
		}

		return new ComplexObjectAttributeValueReader( attributes );
	}

	@Value
	static class ComplexObjectAttributeValueReader implements Function<Object, AttributeValue> {

		final List<FieldAttributeValueReader> fields;

		@Override
		public AttributeValue apply(Object o) {
			val attributes = new HashMap<String, AttributeValue>();

			for ( FieldAttributeValueReader field : fields ) {
				attributes.put( field.getField().getName(), field.read( o ) );
			}

			return AttributeValue.create().withM( attributes );
		}
	}

	interface FieldAttributeValueReader {
		
		Field getField();

		default AttributeValue read( Object object ) {
			try {
				return get( object );
			} catch ( IllegalAccessException e ) {
				throw new IllegalStateException( e );
			}
		}

		AttributeValue get( Object object ) throws IllegalAccessException;
	}

	@Value
	static class BooleanAttributeValue implements FieldAttributeValueReader {

		final Field field;

		@Override
		public AttributeValue get( Object object ) throws IllegalAccessException {
			val v = (Boolean) field.get( object );
			if ( v == null ) return nullValue;
			return AttributeValue.create( v );
		}
	}

	@Value
	static class IntegerAttributeValue implements FieldAttributeValueReader {

		final Field field;

		@Override
		public AttributeValue get( Object object ) throws IllegalAccessException {
			val v = (Integer) field.get( object );
			if ( v == null ) return nullValue;
			return AttributeValue.create( v );
		}
	}

	@Value
	static class LongAttributeValue implements FieldAttributeValueReader {

		final Field field;

		@Override
		public AttributeValue get( Object object ) throws IllegalAccessException {
			val v = (Long) field.get( object );
			if ( v == null ) return nullValue;
			return AttributeValue.create( v );
		}
	}

	@Value
	static class DoubleAttributeValue implements FieldAttributeValueReader {

		final Field field;

		@Override
		public AttributeValue get( Object object ) throws IllegalAccessException {
			return AttributeValue.create( (Double) field.get( object ) );
		}
	}

	@Value
	static class StringAttributeValue implements FieldAttributeValueReader {

		final Field field;

		@Override
		public AttributeValue get( Object object ) throws IllegalAccessException {
			return AttributeValue.create( (String) field.get( object ) );
		}
	}
	
	@Value
	static class ListAttributeValue implements FieldAttributeValueReader {

		final Field field;

		@Override
		public AttributeValue get(Object object) throws IllegalAccessException {
			val list = (List<Object>)field.get( object );
			if ( list == null || list.isEmpty() )
				return nullValue;
			val newList = new ArrayList<AttributeValue>();
			list.forEach( DynamoReflectiveSerializer::serialize );
			return AttributeValue.create().withL( newList );
		}
	}

	@Value
	static class MapAttributeValue implements FieldAttributeValueReader {

		final Field field;

		@Override
		public AttributeValue get(Object object) throws IllegalAccessException {
			val list = (Map<String, Object>)field.get( object );
			if ( list == null || list.isEmpty() )
				return nullValue;
			val newMap = new HashMap<String, AttributeValue>();
			list.forEach( (k,v) -> newMap.put( k, serialize( v ) ) );
			return AttributeValue.create().withM( newMap );
		}
	}

	@Value
	static class ComplexObjectAttributeValue implements FieldAttributeValueReader {

		final Field field;

		@Override
		public AttributeValue get(Object object) throws IllegalAccessException {
			val v = field.get( object );
			if ( v == null )
				return nullValue;
			return serialize( v );
		}
	}
}