code: /*
   * Copyright (C) 2014 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.JsonDeserializer;
  import tools.com.google.gson.JsonSerializer;
  import tools.com.google.gson.TypeAdapter;
  import tools.com.google.gson.TypeAdapterFactory;
  import tools.com.google.gson.annotations.JsonAdapter;
  import tools.com.google.gson.internal.ConstructorConstructor;
  import tools.com.google.gson.reflect.TypeToken;
  
  /**
   * Given a type T, looks for the annotation {@link JsonAdapter} and uses an instance of the
   * specified class as the default type adapter.
   *
   * @since 2.3
   */
  public final class JsonAdapterAnnotationTypeAdapterFactory implements TypeAdapterFactory {
    private final ConstructorConstructor constructorConstructor;
  
    public JsonAdapterAnnotationTypeAdapterFactory(ConstructorConstructor constructorConstructor) {
      this.constructorConstructor = constructorConstructor;
    }
  
    @SuppressWarnings("unchecked")
    @Override
    public <T> TypeAdapter<T> create(Gson gson, TypeToken<T> targetType) {
      Class<? super T> rawType = targetType.getRawType();
      JsonAdapter annotation = rawType.getAnnotation(JsonAdapter.class);
      if (annotation == null) {
        return null;
      }
      return (TypeAdapter<T>) getTypeAdapter(constructorConstructor, gson, targetType, annotation);
    }
  
    @SuppressWarnings({ "unchecked", "rawtypes" }) // Casts guarded by conditionals.
    TypeAdapter<?> getTypeAdapter(ConstructorConstructor constructorConstructor, Gson gson,
        TypeToken<?> type, JsonAdapter annotation) {
      Object instance = constructorConstructor.get(TypeToken.get(annotation.value())).construct();
  
      TypeAdapter<?> typeAdapter;
      if (instance instanceof TypeAdapter) {
        typeAdapter = (TypeAdapter<?>) instance;
      } else if (instance instanceof TypeAdapterFactory) {
        typeAdapter = ((TypeAdapterFactory) instance).create(gson, type);
      } else if (instance instanceof JsonSerializer || instance instanceof JsonDeserializer) {
        JsonSerializer<?> serializer = instance instanceof JsonSerializer
            ? (JsonSerializer) instance
            : null;
        JsonDeserializer<?> deserializer = instance instanceof JsonDeserializer
            ? (JsonDeserializer) instance
            : null;
        typeAdapter = new TreeTypeAdapter(serializer, deserializer, gson, type, null);
      } else {
        throw new IllegalArgumentException("Invalid attempt to bind an instance of "
            + instance.getClass().getName() + " as a @JsonAdapter for " + type.toString()
            + ". @JsonAdapter value must be a TypeAdapter, TypeAdapterFactory,"
            + " JsonSerializer or JsonDeserializer.");
      }
  
      if (typeAdapter != null && annotation.nullSafe()) {
        typeAdapter = typeAdapter.nullSafe();
      }
  
      return typeAdapter;
    }
  }
  