OptionalJsonTypeAdapter.java

/**
 * Copyright (c) 2010, 2013 Darmstadt University of Technology.
 * All rights reserved. This program and the accompanying materials
 * are made available under the terms of the Eclipse Public License v1.0
 * which accompanies this distribution, and is available at
 * http://www.eclipse.org/legal/epl-v10.html
 *
 * Contributors:
 *    Olav Lenz - initial API and implementation.
 */
package org.eclipse.recommenders.utils.gson;

import static com.google.common.base.Optional.absent;
import static com.google.common.base.Optional.fromNullable;

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

import com.google.common.base.Optional;
import com.google.gson.JsonDeserializationContext;
import com.google.gson.JsonDeserializer;
import com.google.gson.JsonElement;
import com.google.gson.JsonParseException;
import com.google.gson.JsonPrimitive;
import com.google.gson.JsonSerializationContext;
import com.google.gson.JsonSerializer;

/**
 * {@link JsonSerializer<Optional<T>>} and {@link JsonDeserializer<Optional<T>>} implementation
 * for {@link Optional}. Examples for the json representation:
 * <ul>
 * <li>Optional.absent() --> "ABSENT"<br>
 * <li>Optional.of("abc") -> "abc"
 * </ul>
 */
public class OptionalJsonTypeAdapter<T> implements JsonSerializer<Optional<T>>, JsonDeserializer<Optional<T>> {

    private static final String ABSENT = "ABSENT"; //$NON-NLS-1$

    @Override
    public JsonElement serialize(Optional<T> src, Type typeOfSrc, JsonSerializationContext context) {
        if (src.isPresent()) {
            return context.serialize(src.get());
        } else {
            return new JsonPrimitive(ABSENT);
        }
    }

    @Override
    public Optional<T> deserialize(JsonElement json, Type typeOfT, JsonDeserializationContext context)
            throws JsonParseException {
        if (json.getAsString().equals(ABSENT)) {
            return absent();
        } else {
            final T entry = context.deserialize(json, ((ParameterizedType) typeOfT).getActualTypeArguments()[0]);
            return fromNullable(entry);
        }
    }
}