Use Cases (Interactors) implementieren
Entwickeln Sie Use Cases, die Entities zur Umsetzung bestimmter Anwendungsfunktionen koordinieren und anwendungsspezifische Geschäftsregeln verkörpern.
Use Cases (Interactors) implementieren ist eine kostenlose Clean Architecture & Design Patterns in Practice-Lektion auf CoddyKit. Dies ist Lektion 2 von 4. Du kannst die komplette Lektion unten kostenlos lesen – dann übst du sie direkt im Browser mit einem integrierten Code-Editor und einem KI-Tutor rund um die Uhr. Sie ist Teil des Clean Architecture & Design Patterns in Practice-Lernpfads, und dein Fortschritt wird über Web und CoddyKit-App synchronisiert. Der Clean Architecture & Design Patterns in Practice-Kurs umfasst insgesamt 4 Lektionen.
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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!
Häufig gestellte Fragen
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Entwickeln Sie Use Cases, die Entities zur Umsetzung bestimmter Anwendungsfunktionen koordinieren und anwendungsspezifische Geschäftsregeln verkörpern. Du übst Clean Architecture & Design Patterns in Practice mit praktischem Code, den du direkt im Browser ausführst, und ein 24/7 KI-Tutor beantwortet deine Fragen während du die Lektion bearbeitest.
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Alle Lektionen in diesem Kurs
- Geschäftsentitäten entwerfen
- Use Cases (Interactors) implementieren
- Input- und Output-Ports
- Geschäftsregeln mit Invarianten durchsetzen