Clean Architecture & Design Patterns in Practice · レッスン

Use Cases（Interactors）の実装

特定のアプリケーション機能を実現するためにEntitiesを調整し、アプリケーション固有のビジネスルールを表すUse Casesを開発します。

「Use Cases（Interactors）の実装」はCoddyKit上の無料Clean Architecture & Design Patterns in Practiceレッスンです。これはレッスン2/4です。下記で完全なレッスンを無料で読むことができます。その後、ブラウザ内の組み込みコードエディタと24時間対応のAIチューターでハンズオン演習できます。これはClean Architecture & Design Patterns in Practice学習パスの一部であり、ウェブとCoddyKitアプリ全体で進捗が同期されます。 Clean Architecture & Design Patterns in Practiceコースには全4レッスンが含まれています。

このレッスンの一部はまだ翻訳されておらず、英語で表示されています。

What are Use Cases (Interactors)?

In Clean Architecture, Use Cases (sometimes called Interactors) are at the heart of your application's logic. They represent the specific tasks or features your application can perform.

Think of them as the orchestrators of your core business entities. They define how your application uses those entities to achieve a goal, like 'create a new user' or 'process an order'.

Role of Use Cases in Clean Architecture

Use Cases sit in the 'Use Cases' layer, just outside the 'Entities' layer. This means:

They depend on Entities.
They do NOT depend on external layers like the UI, databases, or web frameworks.

Their main job is to coordinate the flow of data to and from the Entities and direct the Entities to perform their specific business rules.

Embodying Application Rules

While Entities hold the enterprise-wide business rules (rules true for the entire business, regardless of application), Use Cases embody application-specific business rules.

For example, an 'Order' Entity might have a rule that an order total cannot be negative. A 'Process Order' Use Case might have an application rule that a user must be logged in to place an order, or that certain promotions apply at checkout.

Defining Use Case Boundaries

To keep Use Cases isolated, they communicate with the outside world through interfaces:

Input Port: An interface that defines what data a Use Case expects to receive.
Output Port: An interface that defines what data a Use Case will produce.

These ports ensure the Use Case doesn't know about specific UI components or database implementations.

Anatomy of a Use Case

A typical Use Case is a class with a single public method (e.g., execute or handle). This method usually takes an 'Input Data Transfer Object' (DTO) and returns an 'Output DTO'.

Inside, it interacts with entities and often uses 'Gateway' or 'Repository' interfaces to talk to data storage or external services, without knowing their concrete implementations.

Example: Create User Use Case

Let's consider a CreateUserUseCase. First, we define the simple data structures for input and output. These are plain Java objects (POJOs).

public class CreateUserInput {
  public String name;
  public String email;
}

public class CreateUserOutput {
  public String userId;
  public String message;
  public boolean success;
}

Implementing the Logic

Now, let's see how the CreateUserUseCase orchestrates a User entity and interacts with a UserRepository (an interface) to perform its task.

Try running this example:

public class User {
  private String id;
  private String name;
  private String email;

  public User(String id, String name, String email) {
    this.id = id;
    this.name = name;
    this.email = email;
  }

  public String getId() { return id; }
  public String getName() { return name; }
  public String getEmail() { return email; }
  
  public boolean isValid() { return name != null && !name.isEmpty() && email != null && email.contains("@"); }
}

interface IUserRepository {
  void save(User user);
  String generateId();
}

class InMemoryUserRepository implements IUserRepository {
  @Override
  public void save(User user) {
    System.out.println("Saving user: " + user.getName() + " with ID: " + user.getId());
  }

  @Override
  public String generateId() {
    return "user-" + System.currentTimeMillis();
  }
}

public class CreateUserInput {
  public String name;
  public String email;
}

public class CreateUserOutput {
  public String userId;
  public String message;
  public boolean success;
}

class CreateUserUseCase {
  private final IUserRepository userRepository;

  public CreateUserUseCase(IUserRepository userRepository) {
    this.userRepository = userRepository;
  }

  public CreateUserOutput execute(CreateUserInput input) {
    CreateUserOutput output = new CreateUserOutput();

    if (input.name == null || input.name.isEmpty()) {
      output.success = false;
      output.message = "Name cannot be empty.";
      return output;
    }
    if (input.email == null || !input.email.contains("@")) {
      output.success = false;
      output.message = "Invalid email address.";
      return output;
    }

    String newId = userRepository.generateId();
    User newUser = new User(newId, input.name, input.email);

    if (!newUser.isValid()) {
      output.success = false;
      output.message = "User data is invalid.";
      return output;
    }
    
    userRepository.save(newUser);
    
    output.success = true;
    output.userId = newId;
    output.message = "User created successfully.";
    return output;
  }
}

public class Main {
  public static void main(String[] args) {
    IUserRepository repo = new InMemoryUserRepository();
    CreateUserUseCase useCase = new CreateUserUseCase(repo);

    CreateUserInput input = new CreateUserInput();
    input.name = "Alice";
    input.email = "alice@example.com";

    CreateUserOutput output = useCase.execute(input);

    if (output.success) {
      System.out.println("Result: " + output.message + " ID: " + output.userId);
    } else {
      System.out.println("Error: " + output.message);
    }

    // Test with invalid input
    CreateUserInput invalidInput = new CreateUserInput();
    invalidInput.name = "";
    invalidInput.email = "invalid";
    CreateUserOutput errorOutput = useCase.execute(invalidInput);
    System.out.println("Error test: " + errorOutput.message);
  }
}

Benefits of Use Cases

Using Use Cases brings significant advantages to your software design:

Isolation: Application-specific logic is isolated from UI, database, and frameworks.
Testability: Use Cases can be tested easily in isolation, without needing a UI or database connection.
Independence: Changes in the UI or database technology won't directly impact your core application logic.
Clarity: Each Use Case clearly defines a single feature or task of the application.

Use Case Interaction Flow

When a user interacts with your application, here's a simplified flow involving a Use Case:

UI/Controller: Receives a request (e.g., button click).
Input Port: The controller translates the request into a specific input format for the Use Case.
Use Case: Executes its logic, orchestrating entities and interacting with repositories/gateways.
Output Port: The Use Case provides its result in a generic output format.
Presenter/UI: Transforms the Use Case output into something displayable to the user.

This flow ensures a clean separation of concerns.

Quick Check: Use Case's Role

Based on what you've learned, what is the primary role of a Use Case (Interactor) in Clean Architecture?

Recap: Orchestrating Actions

You've now learned about Use Cases, the application-specific orchestrators in Clean Architecture. They define your app's features, coordinate entities, and encapsulate business rules specific to the application.

By using Input and Output Ports, Use Cases remain independent of external layers, making your core logic highly testable, maintainable, and flexible to change. This is a crucial step towards building robust and adaptable software systems!

よくある質問

「Use Cases（Interactors）の実装」レッスンは無料ですか？

はい。「Use Cases（Interactors）の実装」の完全なテキストはこのウェブで無料で読めます。インタラクティブに演習し（組み込みコードエディタと24時間対応のAIチューター）、Clean Architecture & Design Patterns in Practiceコースの残りをアンロックするには、CoddyKit PROにアップグレードしてください。 Clean Architecture & Design Patterns in Practiceコースには全4レッスンが含まれています。

「Use Cases（Interactors）の実装」で何を学びますか？

特定のアプリケーション機能を実現するためにEntitiesを調整し、アプリケーション固有のビジネスルールを表すUse Casesを開発します。ブラウザで直接実行するハンズオンコードでClean Architecture & Design Patterns in Practiceを演習し、24時間対応のAIチューターがレッスンを進める中での質問に答えます。

Clean Architecture & Design Patterns in Practiceを始めるのに経験は必要ですか？

事前経験は必要ありません。CoddyKitのClean Architecture & Design Patterns in Practiceは初級者から上級者向けに構成されているため、ここから始めるか最初から始めて、自分のペースで進むことができます。これはレッスン2/4です。

「Use Cases（Interactors）の実装」レッスンにはどのくらい時間がかかりますか？

ほとんどのCoddyKitレッスンは約5～10分かかります。各レッスンはコンパクトでインタラクティブなので、着実に進歩し、ウェブとアプリ全体で正確に前回の場所から再開できます。

このClean Architecture & Design Patterns in Practiceレッスンでコードを書いて実行できますか？

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