java/org/eclipse/lsp4j/jsonrpc/json/adapters/CollectionTypeAdapter.java

/******************************************************************************
 * Copyright (c) 2016-2017 TypeFox and others.
 * 
 * This program and the accompanying materials are made available under the
 * terms of the Eclipse Public License v. 2.0 which is available at
 * http://www.eclipse.org/legal/epl-2.0,
 * or the Eclipse Distribution License v. 1.0 which is available at
 * http://www.eclipse.org/org/documents/edl-v10.php.
 * 
 * SPDX-License-Identifier: EPL-2.0 OR BSD-3-Clause
 ******************************************************************************/
package org.eclipse.lsp4j.jsonrpc.json.adapters;

import java.io.IOException;
import java.lang.reflect.Constructor;
import java.lang.reflect.Type;
import java.lang.reflect.TypeVariable;
import java.util.ArrayList;
import java.util.Collection;
import java.util.LinkedHashSet;
import java.util.LinkedList;
import java.util.Queue;
import java.util.Set;
import java.util.SortedSet;
import java.util.TreeSet;
import java.util.function.Supplier;

import com.google.gson.Gson;
import com.google.gson.JsonParseException;
import com.google.gson.TypeAdapter;
import com.google.gson.TypeAdapterFactory;
import com.google.gson.reflect.TypeToken;
import com.google.gson.stream.JsonReader;
import com.google.gson.stream.JsonToken;
import com.google.gson.stream.JsonWriter;

/**
 * A specialized type adapter for collections that can handle single values.
 */
public class CollectionTypeAdapter<E> extends TypeAdapter<Collection<E>> {
	
	public static class Factory implements TypeAdapterFactory {

		@Override
		@SuppressWarnings({ "unchecked" })
		public <T> TypeAdapter<T> create(Gson gson, TypeToken<T> typeToken) {
			if (!Collection.class.isAssignableFrom(typeToken.getRawType()))
				return null;

			Type[] elementTypes = TypeUtils.getElementTypes(typeToken, Collection.class);
			if (elementTypes.length != 1)
				return null;
			Type elementType = elementTypes[0];
			TypeAdapter<?> elementTypeAdapter;
			if (elementType == Object.class)
				elementTypeAdapter = new JsonElementTypeAdapter(gson);
			else
				elementTypeAdapter = gson.getAdapter(TypeToken.get(elementType));
			Supplier<Collection<Object>> constructor = getConstructor((Class<Collection<Object>>) typeToken.getRawType());
			return (TypeAdapter<T>) create(gson, elementType, elementTypeAdapter, constructor);
		}

		@SuppressWarnings({ "unchecked", "rawtypes" })
		protected TypeAdapter<?> create(Gson gson, Type elementType, TypeAdapter<?> elementTypeAdapter, Supplier<Collection<Object>> constructor) {
			return new CollectionTypeAdapter(gson, elementType, elementTypeAdapter, constructor);
		}

		protected <E> Supplier<Collection<E>> getConstructor(Class<? extends Collection<E>> rawType) {
			try {
				Constructor<? extends Collection<E>> constructor = rawType.getDeclaredConstructor();
				return () -> {
					try {
						return constructor.newInstance();
					} catch (Exception e) {
						throw new JsonParseException(e);
					}
				};
			} catch (Exception e) {
				if (SortedSet.class.isAssignableFrom(rawType))
					return () -> new TreeSet<E>();
				else if (Set.class.isAssignableFrom(rawType))
					return () -> new LinkedHashSet<E>();
				else if (Queue.class.isAssignableFrom(rawType))
					return () -> new LinkedList<E>();
				else
					return () -> new ArrayList<E>();
			}
		}

	}

	private final Gson gson;
	private final Type elementType;
	private final TypeAdapter<E> elementTypeAdapter;
	private final Supplier<Collection<E>> constructor;

	public CollectionTypeAdapter(Gson gson, Type elementType, TypeAdapter<E> elementTypeAdapter, Supplier<Collection<E>> constructor) {
		this.gson = gson;
		this.elementType = elementType;
		this.elementTypeAdapter = elementTypeAdapter;
		this.constructor = constructor;
	}

	@Override
	public Collection<E> read(JsonReader in) throws IOException {
		JsonToken peek = in.peek();
		if (peek == JsonToken.NULL) {
			in.nextNull();
			return null;
		} else if (peek == JsonToken.BEGIN_ARRAY) {
			Collection<E> collection = constructor.get();
			in.beginArray();
			while (in.hasNext()) {
				E instance = elementTypeAdapter.read(in);
				collection.add(instance);
			}
			in.endArray();
			return collection;
		} else {
			Collection<E> collection = constructor.get();
			E instance = elementTypeAdapter.read(in);
			collection.add(instance);
			return collection;
		}
	}

	@Override
	public void write(JsonWriter out, Collection<E> collection) throws IOException {
		if (collection == null) {
			out.nullValue();
			return;
		}
		out.beginArray();
		for (E element : collection) {
			if (element != null && elementType != element.getClass()
					&& (elementType instanceof TypeVariable<?> || elementType instanceof Class<?>)) {
				@SuppressWarnings("unchecked")
				TypeAdapter<E> runtimeTypeAdapter = (TypeAdapter<E>) gson.getAdapter(TypeToken.get(element.getClass()));
				runtimeTypeAdapter.write(out, element);
			} else {
				elementTypeAdapter.write(out, element);
			}
		}
		out.endArray();
	}
}