CODESAMPLE

Clean Architecture - Java

Clean Architecture Java

The Clean Architecture pattern aims to create systems independent of frameworks, databases, UI, and any external agency. It achieves this through layered architecture with an “inward rule” – dependencies point only inwards. The core business logic (Entities and Use Cases) resides in the inner layers, while outer layers (Interface Adapters & Frameworks and Drivers) contain implementation details. This promotes testability, maintainability, and flexibility.

The provided Java example demonstrates a simplified Clean Architecture for a user data management system. The entities package contains the User entity. usecases define the core business logic like RegisterUser. The interfaceadapters package features a UserPresenter which adapts data for presentation, and a UserGateway interface defining data access. Finally, frameworks includes a concrete UserRepository implementation using an in-memory data store and a simple CLI Main class acting as the driver. Dependency Injection is used to decouple layers. This structure aligns with Java’s packaging conventions and OOP principles, enhancing readability and scalability.

// entities/User.java
package entities;

public class User {
    private final String username;
    private final String email;

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

    public String getUsername() {
        return username;
    }

    public String getEmail() {
        return email;
    }

    @Override
    public String toString() {
        return "User{" +
                "username='" + username + '\'' +
                ", email='" + email + '\'' +
                '}';
    }
}

// usecases/RegisterUser.java
package usecases;

import entities.User;
import interfaces.UserGateway;

public class RegisterUser {
    private final UserGateway userGateway;

    public RegisterUser(UserGateway userGateway) {
        this.userGateway = userGateway;
    }

    public boolean register(String username, String email) {
        User newUser = new User(username, email);
        return userGateway.saveUser(newUser);
    }
}

// interfaceadapters/UserPresenter.java
package interfaceadapters;

import entities.User;

public class UserPresenter {
    public static String presentUser(User user) {
        return "Username: " + user.getUsername() + ", Email: " + user.getEmail();
    }
}

// interfaces/UserGateway.java
package interfaces;

import entities.User;

public interface UserGateway {
    boolean saveUser(User user);
    User getUserByUsername(String username);
}

// frameworks/UserRepository.java
package frameworks;

import entities.User;
import interfaces.UserGateway;
import java.util.HashMap;
import java.util.Map;

public class UserRepository implements UserGateway {
    private final Map<String, User> users = new HashMap<>();

    @Override
    public boolean saveUser(User user) {
        if (users.containsKey(user.getUsername())) {
            return false;
        }
        users.put(user.getUsername(), user);
        return true;
    }

    @Override
    public User getUserByUsername(String username) {
        return users.get(username);
    }
}

// frameworks/Main.java
package frameworks;

import usecases.RegisterUser;

public class Main {
    public static void main(String[] args) {
        UserRepository userRepository = new UserRepository();
        RegisterUser registerUser = new RegisterUser(userRepository);

        boolean registered = registerUser.register("john.doe", "john.doe@example.com");
        if (registered) {
            System.out.println("User registered successfully!");
        } else {
            System.out.println("User registration failed.");
        }
    }
}