CollectionTypeAdapter.java

/*
 * Copyright (C) 2011 Google Inc.
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *      http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

package com.smartandroid.sa.json.internal.bind;

import java.io.IOException;
import java.lang.reflect.Constructor;
import java.lang.reflect.Type;
import java.util.ArrayList;
import java.util.Collection;
import java.util.LinkedHashSet;
import java.util.List;
import java.util.Set;

import com.smartandroid.sa.json.internal.$Gson$Types;
import com.smartandroid.sa.json.reflect.TypeToken;
import com.smartandroid.sa.json.stream.JsonReader;
import com.smartandroid.sa.json.stream.JsonToken;
import com.smartandroid.sa.json.stream.JsonWriter;

/**
 * Adapt a homogeneous collection of objects.
 */
public final class CollectionTypeAdapter<E> extends TypeAdapter<Collection<E>> {
	public static final Factory FACTORY = new Factory() {
		public <T> TypeAdapter<T> create(MiniGson context,
				TypeToken<T> typeToken) {
			Type type = typeToken.getType();

			Class<? super T> rawType = typeToken.getRawType();
			if (!Collection.class.isAssignableFrom(rawType)) {
				return null;
			}

			Type elementType = $Gson$Types.getCollectionElementType(type,
					rawType);
			TypeAdapter<?> elementTypeAdapter = context.getAdapter(TypeToken
					.get(elementType));

			Class<?> constructorType;

			if (rawType == List.class || rawType == Collection.class) {
				constructorType = ArrayList.class;
			} else if (rawType == Set.class) {
				constructorType = LinkedHashSet.class;
			} else {
				constructorType = rawType;
			}

			Constructor<?> constructor;
			try {
				constructor = constructorType.getConstructor();
			} catch (NoSuchMethodException e) {
				return null;
			}

			@SuppressWarnings("unchecked")
			// create() doesn't define a type parameter
			TypeAdapter<T> result = new CollectionTypeAdapter(context,
					elementType, elementTypeAdapter, constructor);
			return result;
		}
	};

	private final TypeAdapter<E> elementTypeAdapter;
	private final Constructor<? extends Collection<E>> constructor;

	public CollectionTypeAdapter(MiniGson context, Type elementType,
			TypeAdapter<E> elementTypeAdapter,
			Constructor<? extends Collection<E>> constructor) {
		this.elementTypeAdapter = new TypeAdapterRuntimeTypeWrapper<E>(context,
				elementTypeAdapter, elementType);
		this.constructor = constructor;
	}

	public Collection<E> read(JsonReader reader) throws IOException {
		if (reader.peek() == JsonToken.NULL) {
			reader.nextNull(); // TODO: does this belong here?
			return null;
		}

		Collection<E> collection = Reflection.newInstance(constructor);
		reader.beginArray();
		while (reader.hasNext()) {
			E instance = elementTypeAdapter.read(reader);
			collection.add(instance);
		}
		reader.endArray();
		return collection;
	}

	public void write(JsonWriter writer, Collection<E> collection)
			throws IOException {
		if (collection == null) {
			writer.nullValue(); // TODO: better policy here?
			return;
		}

		writer.beginArray();
		for (E element : collection) {
			elementTypeAdapter.write(writer, element);
		}
		writer.endArray();
	}
}