如何在spring-data-jpa中进行投影

public interface UserProjection {
    String getUsername();
    String getEmail();
}

@Repository
public interface UserRepository extends JpaRepository<User, Long> {
    List<UserProjection> findByUsername(String username);
}

public class UserDTO {
    private String username;
    private String email;

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

    // getters and setters
}

@Repository
public interface UserRepository extends JpaRepository<User, Long> {
    @Query("SELECT new com.example.UserDTO(u.username, u.email) FROM User u WHERE u.username = :username")
    List<UserDTO> findByUsername(@Param("username") String username);
}

public interface UserProjection {
    String getUsername();
    String getEmail();
}

@Repository
public interface UserRepository extends JpaRepository<User, Long> {
    @Query("SELECT u.username AS username, u.email AS email FROM User u WHERE u.username = :username")
    List<UserProjection> findByUsername(@Param("username") String username);
}