ImmutableSetSerializer.java

package de.javakaffee.kryoserializers.guava;

import com.esotericsoftware.kryo.Kryo;
import com.esotericsoftware.kryo.Serializer;
import com.esotericsoftware.kryo.io.Input;
import com.esotericsoftware.kryo.io.Output;
import com.google.common.collect.ImmutableSet;
import com.google.common.collect.Sets;

/**
 * A kryo {@link Serializer} for guava-libraries {@link ImmutableSet}.
 *
 *@implNote ImmutableSet builder would be a little bit more efficient for less than five elements
 *(the array.clone as done by copyOf is saved), for more elements copyOf seems to get more efficient.
 */
public class ImmutableSetSerializer extends Serializer<ImmutableSet<Object>> {

    private static final boolean DOES_NOT_ACCEPT_NULL = false;
    private static final boolean IMMUTABLE = true;

    public ImmutableSetSerializer() {
        super(DOES_NOT_ACCEPT_NULL, IMMUTABLE);
    }

    @Override
    public void write(Kryo kryo, Output output, ImmutableSet<Object> object) {
        output.writeInt(object.size(), true);
        for (Object elm : object) {
            kryo.writeClassAndObject(output, elm);
        }
    }

    @Override
    public ImmutableSet<Object> read(Kryo kryo, Input input, Class<ImmutableSet<Object>> type) {
        final int size = input.readInt(true);
        ImmutableSet.Builder<Object> builder = ImmutableSet.builder();
        for (int i = 0; i < size; ++i) {
            builder.add(kryo.readClassAndObject(input));
        }
        return builder.build();
    }

    /**
     * Creates a new {@link ImmutableSetSerializer} and registers its serializer
     * for the several ImmutableSet related classes.
     *
     * @param kryo the {@link Kryo} instance to set the serializer on
     */
    public static void registerSerializers(final Kryo kryo) {

        // ImmutableList (abstract class)
        //  +- EmptyImmutableSet
        //  |   EmptyImmutableSet
        //  +- SingletonImmutableSet
        //  |   Optimized for Set with only 1 element.
        //  +- RegularImmutableSet
        //  |   RegularImmutableList
        //  +- EnumImmutableSet
        //  |   EnumImmutableSet

        final ImmutableSetSerializer serializer = new ImmutableSetSerializer();

        kryo.register(ImmutableSet.class, serializer);

        // Note:
        //  Only registering above is good enough for serializing/deserializing.
        //  but if using Kryo#copy, following is required.

        kryo.register(ImmutableSet.of().getClass(), serializer);
        kryo.register(ImmutableSet.of(1).getClass(), serializer);
        kryo.register(ImmutableSet.of(1,2,3).getClass(), serializer);

        kryo.register(Sets.immutableEnumSet(SomeEnum.A, SomeEnum.B, SomeEnum.C).getClass(), serializer);
    }

    private enum SomeEnum {
        A, B, C
    }
}