Optional Type Adapter for Gson (using the Optional gist located elsewhere)

Optional.java

package com.derp.gsonoptional;

/**
 * Created by fdoyle on 3/20/15.
 */

import com.google.gson.JsonArray;
import com.google.gson.JsonDeserializationContext;
import com.google.gson.JsonDeserializer;
import com.google.gson.JsonElement;
import com.google.gson.JsonParseException;
import com.google.gson.JsonSerializationContext;
import com.google.gson.JsonSerializer;

import java.lang.reflect.ParameterizedType;
import java.lang.reflect.Type;

/**
 * Created by fdoyle on 12/18/14.
 * <p/>
 * a backport of the java 8 optional type
 */
public class Optional<T> {
    private T value;

    static <T> Optional<T> empty() {
        return new Optional<>();
    }

    public boolean equals(Object obj) {
        //todo
        return false;
    }

    public T get() {
        return value;
    }

    public void ifPresent(Consumer<? super T> consumer) {
        consumer.accept(value);
    }

    public boolean isPresent() {
        return value != null;
    }

    //requires not null
    public static <T> Optional<T> of(T value) {
        if (value == null) {
            throw new NullPointerException("value must be non-null");
        }
        Optional<T> optional = new Optional<>();
        optional.value = value;
        return optional;
    }

    public static <T> Optional<T> ofNullable(T value) {
        Optional<T> optional = new Optional<>();
        optional.value = value;
        return optional;
    }

    public T orElse(T other) {
        if (value == null) {
            return other;
        } else {
            return value;
        }
    }

    @Override
    public String toString() {
        if (value == null) {
            return super.toString() + " value: null";
        } else {
            return super.toString() + " value: " + value.toString();
        }
    }

    public abstract static class Consumer<T> {
        public abstract void accept(T t);

        public Consumer<T> andThen(final Consumer<? super T> after) {
            if (after == null) {
                throw new NullPointerException();
            }
            final Consumer thisConsumer = this;
            return new Consumer<T>() {
                @Override
                public void accept(T t) {
                    thisConsumer.accept(t); //in java 8, this "consumer" is just a function,
                    after.accept(t);
                }
            };
        }
    }

    //no promises on these, totally untested, probably doesn't even work

    public class serializer implements JsonDeserializer<Optional<T>>, JsonSerializer<Optional<T>> {

        @Override
        public Optional<T> deserialize(JsonElement json, Type typeOfT, JsonDeserializationContext context)
                throws JsonParseException {
            final JsonArray asJsonArray = json.getAsJsonArray();
            final JsonElement jsonElement = asJsonArray.get(0);
            final T value = context.deserialize(jsonElement, ((ParameterizedType) typeOfT).getActualTypeArguments()[0]);
            return Optional.ofNullable(value);
        }

        @Override
        public JsonElement serialize(Optional<T> src, Type typeOfSrc, JsonSerializationContext context) {
            final JsonElement element = context.serialize(src.orElse(null));
            final JsonArray result = new JsonArray();
            result.add(element);
            return result;
        }
    }
}

OptionalTypeAdapter.java

package com.derp.gsonoptional;

import com.google.gson.JsonDeserializationContext;
import com.google.gson.JsonDeserializer;
import com.google.gson.JsonElement;
import com.google.gson.JsonParseException;
import com.google.gson.JsonSerializationContext;
import com.google.gson.JsonSerializer;

import java.lang.reflect.ParameterizedType;
import java.lang.reflect.Type;

/**
 * Created by fdoyle on 3/20/15.
 */
public class OptionalTypeAdapter implements JsonDeserializer<Optional<?>>, JsonSerializer<Optional<?>> {

    @Override
    public Optional deserialize(JsonElement json, Type typeOfT, JsonDeserializationContext context)
            throws JsonParseException {
        final Object value = context.deserialize(json, ((ParameterizedType) typeOfT).getActualTypeArguments()[0]);
        return Optional.ofNullable(value);
    }

    @Override
    public JsonElement serialize(Optional<?> src, Type typeOfSrc, JsonSerializationContext context) {
        return context.serialize(src.orElse(null));
    }
}