code: /*
   * 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 tools.com.google.gson.internal.bind;
  
  import tools.com.google.gson.Gson;
  import tools.com.google.gson.TypeAdapter;
  import tools.com.google.gson.TypeAdapterFactory;
  import tools.com.google.gson.internal.$Gson$Types;
  import tools.com.google.gson.internal.ConstructorConstructor;
  import tools.com.google.gson.internal.ObjectConstructor;
  import tools.com.google.gson.reflect.TypeToken;
  import tools.com.google.gson.stream.JsonReader;
  import tools.com.google.gson.stream.JsonToken;
  import tools.com.google.gson.stream.JsonWriter;
  import java.io.IOException;
  import java.lang.reflect.Type;
  import java.util.Collection;
  
  /**
   * Adapt a homogeneous collection of objects.
   */
  public final class CollectionTypeAdapterFactory implements TypeAdapterFactory {
    private final ConstructorConstructor constructorConstructor;
  
    public CollectionTypeAdapterFactory(ConstructorConstructor constructorConstructor) {
      this.constructorConstructor = constructorConstructor;
    }
  
    @Override
    public <T> TypeAdapter<T> create(Gson gson, 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 = gson.getAdapter(TypeToken.get(elementType));
      ObjectConstructor<T> constructor = constructorConstructor.get(typeToken);
  
      @SuppressWarnings({"unchecked", "rawtypes"}) // create() doesn't define a type parameter
      TypeAdapter<T> result = new Adapter(gson, elementType, elementTypeAdapter, constructor);
      return result;
    }
  
    private static final class Adapter<E> extends TypeAdapter<Collection<E>> {
      private final TypeAdapter<E> elementTypeAdapter;
      private final ObjectConstructor<? extends Collection<E>> constructor;
  
      public Adapter(Gson context, Type elementType,
          TypeAdapter<E> elementTypeAdapter,
          ObjectConstructor<? extends Collection<E>> constructor) {
        this.elementTypeAdapter =
            new TypeAdapterRuntimeTypeWrapper<E>(context, elementTypeAdapter, elementType);
        this.constructor = constructor;
      }
  
      @Override public Collection<E> read(JsonReader in) throws IOException {
        if (in.peek() == JsonToken.NULL) {
          in.nextNull();
          return null;
        }
  
        Collection<E> collection = constructor.construct();
        in.beginArray();
        while (in.hasNext()) {
          E instance = elementTypeAdapter.read(in);
          collection.add(instance);
        }
        in.endArray();
        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) {
          elementTypeAdapter.write(out, element);
        }
        out.endArray();
      }
    }
  }
  