@Override public void onViewCreated(View view, Bundle savedInstanceState) {
    super.onViewCreated(view, savedInstanceState);
    this.userListPresenter.setView(this);
    if (savedInstanceState == null) {
      this.loadUserList();
    }
  }

  private void loadUserList() {
    // Presenterへの呼び出し!!
    this.userListPresenter.initialize();
  }

  /**
   * Initializes the presenter by start retrieving the user list.
   */
  public void initialize() {
    this.loadUserList();
  }

  /**
   * Loads all users.
   */
  private void loadUserList() {
    this.hideViewRetry();
    this.showViewLoading();
    this.getUserList();
  }
  private void hideViewRetry() {
    this.viewListView.hideRetry();
  }
  private void showViewLoading() {
    // ViewでProgressBarを出す
    this.viewListView.showLoading();
  }
  private void getUserList() {
    // UseCaseの呼び出しして、RxJavaのObserverを渡す
    this.getUserListUseCase.execute(new UserListObserver(), null);
  }

public abstract class UseCase<T, Params> {
  // このメソッドはそれぞれのUseCaseが実装する
  abstract Observable<T> buildUseCaseObservable(Params params);

  public void execute(DisposableObserver<T> observer, Params params) {
    Preconditions.checkNotNull(observer);
    // buildUseCaseObservable()を引数のobserverで観測する。
    final Observable<T> observable = this.buildUseCaseObservable(params)
        .subscribeOn(Schedulers.from(threadExecutor))
        .observeOn(postExecutionThread.getScheduler());
    addDisposable(observable.subscribeWith(observer));
  }

public class GetUserList extends UseCase<List<User>, Void> {

  private final UserRepository userRepository;

  @Inject
  GetUserList(UserRepository userRepository, ThreadExecutor threadExecutor,
      PostExecutionThread postExecutionThread) {
    super(threadExecutor, postExecutionThread);
    this.userRepository = userRepository;
  }

  @Override Observable<List<User>> buildUseCaseObservable(Void unused) {
    return this.userRepository.users();
  }
}

@Singleton
public class UserDataRepository implements UserRepository {
  @Override public Observable<List<User>> users() {
    //we always get all users from the cloud
    final UserDataStore userDataStore = this.userDataStoreFactory.createCloudDataStore();
    // ここでUserEntityの取得とUserクラスへの変換を行う！！
    return userDataStore.userEntityList().map(this.userEntityDataMapper::transform);
  }

  // こちらは今回使わないが、参考のため。
  // DiskにあればDBをDataSourceに使い、なければAPIを使う
  /**
   * Create {@link UserDataStore} from a user id.
   */
  public UserDataStore create(int userId) {
    UserDataStore userDataStore;

    if (!this.userCache.isExpired() && this.userCache.isCached(userId)) {
      userDataStore = new DiskUserDataStore(this.userCache);
    } else {
      userDataStore = createCloudDataStore();
    }

    return userDataStore;
  }

  // こちらが今回使うメソッド。基本的にAPIアクセスを行うCloudUserDataStoreを返す
  /**
   * Create {@link UserDataStore} to retrieve data from the Cloud.
   */
  public UserDataStore createCloudDataStore() {
    final UserEntityJsonMapper userEntityJsonMapper = new UserEntityJsonMapper();
    final RestApi restApi = new RestApiImpl(this.context, userEntityJsonMapper);

    return new CloudUserDataStore(restApi, this.userCache);
  }

  /**
   * Transform a {@link UserEntity} into an {@link User}.
   *
   * @param userEntity Object to be transformed.
   * @return {@link User} if valid {@link UserEntity} otherwise null.
   */
  public User transform(UserEntity userEntity) {
    User user = null;
    if (userEntity != null) {
      user = new User(userEntity.getUserId());
      user.setCoverUrl(userEntity.getCoverUrl());
      user.setFullName(userEntity.getFullname());
      user.setDescription(userEntity.getDescription());
      user.setFollowers(userEntity.getFollowers());
      user.setEmail(userEntity.getEmail());
    }
    return user;
  }

  /**
   * Transform a List of {@link UserEntity} into a Collection of {@link User}.
   *
   * @param userEntityCollection Object Collection to be transformed.
   * @return {@link User} if valid {@link UserEntity} otherwise null.
   */
  public List<User> transform(Collection<UserEntity> userEntityCollection) {
    final List<User> userList = new ArrayList<>(20);
    for (UserEntity userEntity : userEntityCollection) {
      final User user = transform(userEntity);
      if (user != null) {
        userList.add(user);
      }
    }
    return userList;
  }

public class UserEntity {

  @SerializedName("id")
  private int userId;

  @SerializedName("cover_url")
  private String coverUrl;

  @SerializedName("full_name")
  private String fullname;

public class User {

  private final int userId;

  public User(int userId) {
    this.userId = userId;
  }

  private String coverUrl;
  private String fullName;

  private void getUserList() {
    // UseCaseの呼び出しして、RxJavaのObserverを渡す
    this.getUserListUseCase.execute(new UserListObserver(), null);
  }

  private final class UserListObserver extends DefaultObserver<List<User>> {

   ...
    @Override public void onNext(List<User> users) {
      UserListPresenter.this.showUsersCollectionInView(users);
    }
  }

  private void showUsersCollectionInView(Collection<User> usersCollection) {
    // ここでUserクラスからUserModelクラスへ変換を行う！！
    final Collection<UserModel> userModelsCollection =
        this.userModelDataMapper.transform(usersCollection);
    this.viewListView.renderUserList(userModelsCollection);
  }

  /**
   * Transform a {@link User} into an {@link UserModel}.
   *
   * @param user Object to be transformed.
   * @return {@link UserModel}.
   */
  public UserModel transform(User user) {
    if (user == null) {
      throw new IllegalArgumentException("Cannot transform a null value");
    }
    final UserModel userModel = new UserModel(user.getUserId());
    userModel.setCoverUrl(user.getCoverUrl());
    userModel.setFullName(user.getFullName());
    userModel.setEmail(user.getEmail());
    userModel.setDescription(user.getDescription());
    userModel.setFollowers(user.getFollowers());

    return userModel;
  }

  /**
   * Transform a Collection of {@link User} into a Collection of {@link UserModel}.
   *
   * @param usersCollection Objects to be transformed.
   * @return List of {@link UserModel}.
   */
  public Collection<UserModel> transform(Collection<User> usersCollection) {
    Collection<UserModel> userModelsCollection;

    if (usersCollection != null && !usersCollection.isEmpty()) {
      userModelsCollection = new ArrayList<>();
      for (User user : usersCollection) {
        userModelsCollection.add(transform(user));
      }
    } else {
      userModelsCollection = Collections.emptyList();
    }

    return userModelsCollection;
  }

public class UserModel {

  private final int userId;

  public UserModel(int userId) {
    this.userId = userId;
  }

  private String coverUrl;
  private String fullName;

  @Override public void onBindViewHolder(UserViewHolder holder, final int position) {
    final UserModel userModel = this.usersCollection.get(position);
    holder.textViewTitle.setText(userModel.getFullName());
    holder.itemView.setOnClickListener(new View.OnClickListener() {
      @Override public void onClick(View v) {
        if (UsersAdapter.this.onItemClickListener != null) {
          UsersAdapter.this.onItemClickListener.onUserItemClicked(userModel);
        }
      }
    });
  }