Pseudo code for layered architecture.

MainContainer.java

public class MainContainer {
  public static void main(String[] args) {
    // Frameworks and drivers
    DatabaseDriver jdbcDatabaseDriver = new MysqlDatabaseDriver();
    
    // Interface adapters
    UserRepository userRepository = new UserMySQLRepository(jdbcDatabaseDriver);
    
    // Use cases.
    UserBusinessUseCases userBusinessCases = new UserBusinessCases(userRepository);
    
    // Interface adapter
    WebService userServiceResource = new UserServiceResource(userBusinessCases);
    
    // Frameworks and drivers
    Webserver webserver = new Webserver();
    webserver.registerService(userServiceResource);
    
    webserver.startServiceOn("http://localhost:8080");
  }
}

// Being used everywhere.
class domain.User {
  public UserIdentifier id;
  public Username username;
}