Clean Architecture & Design Patterns in Practice · レッスン

InputとOutputのPorts

Input PortsとOutput Ports（インターフェース）が、Use Casesと外部層の通信境界を定義する仕組みを理解します。

「InputとOutputのPorts」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3/4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 Input & Output Ports?

In Clean Architecture, "Ports" are crucial interfaces that define how different layers communicate. They act like contracts.

Think of them as the "sockets" of your application's core logic. They specify what goes in (Input) and what comes out (Output).

Defining Input Ports

An Input Port is an interface defined by the Use Case layer. It declares the methods that an external layer (like a UI controller) can call to interact with the Use Case.

It's the "what you can do" contract for the Use Case.
It ensures the Use Case doesn't know about the UI or external callers.

Input Port: User Login

Here's a simple Input Port for a user login feature. It defines the operations the Use Case expects.

public interface UserLoginInputPort {
  void login(String username, String password);
}

public class UserLoginUseCase implements UserLoginInputPort {
  @Override
  public void login(String username, String password) {
    // Business logic for login
    System.out.println("Attempting login for: " + username);
    if (username.equals("admin") && password.equals("pass")) {
      System.out.println("Login successful!");
    } else {
      System.out.println("Login failed.");
    }
  }

  public static void main(String[] args) {
    UserLoginInputPort loginService = new UserLoginUseCase();
    loginService.login("admin", "pass");
    loginService.login("user", "123");
  }
}

Defining Output Ports

An Output Port is also an interface, defined by the Use Case layer. It declares the methods that the Use Case will call to deliver results or interact with external services (like a database or UI presenter).

It's the "what I need to tell you" contract.
It keeps the Use Case unaware of specific implementations (e.g., how results are displayed).

Output Port: Login Presenter

This Output Port defines how the login result should be presented or handled. The Use Case calls these methods, but doesn't know how they are implemented.

public interface UserLoginOutputPort {
  void presentLoginSuccess(String username);
  void presentLoginFailure(String message);
}

public class ConsolePresenter implements UserLoginOutputPort {
  @Override
  public void presentLoginSuccess(String username) {
    System.out.println("Welcome, " + username + "!");
  }

  @Override
  public void presentLoginFailure(String message) {
    System.out.println("Error: " + message);
  }

  public static void main(String[] args) {
    UserLoginOutputPort presenter = new ConsolePresenter();
    presenter.presentLoginSuccess("Alice");
    presenter.presentLoginFailure("Invalid credentials.");
  }
}

How Use Cases Use Ports

The Use Case (or Interactor) depends on these port interfaces. It takes an Input Port as its public method and receives an Output Port through its constructor or method parameters.

This means the Use Case only knows about abstractions, not concrete implementations.

Use Case Connecting Ports

Here, our UserLoginUseCase now uses both ports. Notice it doesn't know if it's talking to a web UI, a mobile app, or a console!

public interface UserLoginInputPort {
  void login(String username, String password);
}

public interface UserLoginOutputPort {
  void presentLoginSuccess(String username);
  void presentLoginFailure(String message);
}

public class UserLoginUseCase implements UserLoginInputPort {
  private final UserLoginOutputPort outputPort;

  public UserLoginUseCase(UserLoginOutputPort outputPort) {
    this.outputPort = outputPort;
  }

  @Override
  public void login(String username, String password) {
    if (username.equals("admin") && password.equals("pass")) {
      outputPort.presentLoginSuccess(username);
    } else {
      outputPort.presentLoginFailure("Invalid credentials.");
    }
  }

  public static void main(String[] args) {
    // In real app, this would be wired by a framework
    UserLoginOutputPort presenter = new ConsolePresenter(); // From Scene 5
    UserLoginInputPort loginService = new UserLoginUseCase(presenter);

    loginService.login("admin", "pass");
    loginService.login("user", "wrong");
  }
}

class ConsolePresenter implements UserLoginOutputPort {
  @Override
  public void presentLoginSuccess(String username) {
    System.out.println("Welcome, " + username + "!");
  }

  @Override
  public void presentLoginFailure(String message) {
    System.out.println("Error: " + message);
  }
}

Ports and the Dependency Rule

The use of Ports perfectly adheres to the Dependency Rule. The Use Case layer (core business logic) depends on interfaces (the Ports).

The outer layers (like UI or databases) then implement these interfaces, providing the concrete details without the core knowing about them.

Why Use Ports?

Ports offer powerful advantages:

Decoupling: The Use Case is isolated from UI, database, or external services.
Testability: You can easily mock or stub these interfaces for robust unit testing of Use Cases.
Flexibility: You can swap out implementations (e.g., change database) without touching core logic.
Clarity: They clearly define the boundaries and interactions of your application's core.

Quick Check: Port Roles

Consider the roles of Input and Output Ports in Clean Architecture.

Recap: Ports as Boundaries

We learned that Input Ports are interfaces defining what a Use Case expects, acting as entry points.

Output Ports are interfaces defining what a Use Case delivers or needs from external services.

Together, they enforce the Dependency Rule, ensuring our core business logic remains independent, testable, and flexible.

よくある質問

「InputとOutputのPorts」レッスンは無料ですか？

はい。「InputとOutputのPorts」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。

「InputとOutputのPorts」で何を学びますか？

Input PortsとOutput Ports（インターフェース）が、Use Casesと外部層の通信境界を定義する仕組みを理解します。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3/4です。

「InputとOutputのPorts」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。

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