StringToValueMapTypeAdapter.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.ParameterizedType;
import java.lang.reflect.Type;
import java.util.LinkedHashMap;
import java.util.Map;

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 map whose keys are strings.
 */
public final class StringToValueMapTypeAdapter<V> extends
		TypeAdapter<Map<String, V>> {
	public static final Factory FACTORY = new Factory() {
		public <T> TypeAdapter<T> create(MiniGson context,
				TypeToken<T> typeToken) {
			Type type = typeToken.getType();
			if (!(type instanceof ParameterizedType)) {
				return null;
			}

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

			Type[] keyAndValueTypes = $Gson$Types.getMapKeyAndValueTypes(type,
					rawType);
			if (keyAndValueTypes[0] != String.class) {
				return null;
			}
			TypeAdapter<?> valueAdapter = context.getAdapter(TypeToken
					.get(keyAndValueTypes[1]));

			Constructor<?> constructor;
			try {
				Class<?> constructorType = (rawType == Map.class) ? LinkedHashMap.class
						: rawType;
				constructor = constructorType.getConstructor();
			} catch (NoSuchMethodException e) {
				return null;
			}

			@SuppressWarnings("unchecked")
			// we don't define a type parameter for the key or value types
			TypeAdapter<T> result = new StringToValueMapTypeAdapter(
					valueAdapter, constructor);
			return result;
		}
	};

	private final TypeAdapter<V> valueTypeAdapter;
	private final Constructor<? extends Map<String, V>> constructor;

	public StringToValueMapTypeAdapter(TypeAdapter<V> valueTypeAdapter,
			Constructor<? extends Map<String, V>> constructor) {
		this.valueTypeAdapter = valueTypeAdapter;
		this.constructor = constructor;
	}

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

		Map<String, V> map = Reflection.newInstance(constructor);
		reader.beginObject();
		while (reader.hasNext()) {
			String key = reader.nextName();
			V value = valueTypeAdapter.read(reader);
			map.put(key, value);
		}
		reader.endObject();
		return map;
	}

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

		writer.beginObject();
		for (Map.Entry<String, V> entry : map.entrySet()) {
			writer.name(entry.getKey());
			valueTypeAdapter.write(writer, entry.getValue());
		}
		writer.endObject();
	}
}