How to get distinct count of list on more than one property?

Question

I am trying to save list of admins and I need to validate unique username and email address. First, I need to validate that condition within the list of my request DTOs and then check it one at a time again with the list that is already saved in my database.

I checked RequestDTO using distinct once for username and email address. Then again, I checked with the database. Doing this way, multiple loops are executed.

I referred following ways already :

Java stream that is distinct by more than one property

java 8 how to get distinct list on more than one property

Java 8 Distinct by property

@Getter
@Setter
@Builder
@AllArgsConstructor
@NoArgsConstructor
@ApiModel(value = "This is admin request class")
public class AdminRequestDTO implements Serializable {

    @ApiModelProperty(value = "This is the id of admin")
    private Long id;

    @ApiModelProperty(value = "This is the username of admin")
    private String username;

    @ApiModelProperty(value = "This is full name of admin")
    private String fullName;

    @ApiModelProperty(value = "This is the email address of admin")
    private String emailAddress;


    @ApiModelProperty(value = "This is the status of admin")
    private Character status;
}

@Entity
@Getter
@Setter
@Table(name = "admin")
public class Admin implements Serializable {
  @Id
  @GeneratedValue(strategy = GenerationType.IDENTITY)
  private Long id;

  @Column(name = "username")
  private String username;

  @Column(name = "fullname")
  private String fullName;

  @Column(name = "password")
  private String password;

  @Column(name = "email_address", length = 200)
  private String emailAddress;
}

public void saveAdmin(List<AdminRequestDTO> adminRequestDTO) {

    validateAdminRequestDTO.accept(adminRequestDTO);

    List<Admin> admin = adminRequestDTO.stream().map(requestDTO -> {

        /*CHECK IF USERNAME AND EMAIL ADDRESS IN REQUESTDTO EXISTS IN DATABASE, ID IT DOES, THEN THROW EXCEPTION*/
/*ELSE CONVERT */

        Admin admin1 = new Admin();
        admin1.setUsername(requestDTO.getUsername());
        /*SET OTHER REQUEST DTOS*/
        return admin1;
    }).collect(Collectors.toList());

    /*SAVE ADMIN*/
    adminRepository.saveAll(admin);
}

  public Consumer<List<AdminRequestDTO>> validateAdminRequestDTO = (requestDTO) -> {

        boolean checkIfRequestHaveSameUsername = requestDTO.stream().map(AdminRequestDTO::getUsername)
                .distinct().count() < requestDTO.size();

        boolean checkIfRequestHaveSameEmailAddress = requestDTO.stream().map(AdminRequestDTO::getEmailAddress)
                .distinct().count() < requestDTO.size();

        if (checkIfRequestHaveSameUsername)
            throw new DataDuplicationException(AdminMessageConstants.DUPLICATE_USERNAME_MESSAGE,
                    AdminMessageConstants.DUPLICATE_USERNAME_DEVELOPER_MESSAGE);

        if (checkIfRequestHaveSameEmailAddress)
            throw new DataDuplicationException(AdminMessageConstants.DUPLICATE_EMAILADDRESS_MESSAGE,
                    AdminMessageConstants.DUPLICATE_EMAILADDRESS_DEVELOPER_MESSAGE);
    };

 public Consumer<AdminRequestDTO> validateAdmin = (requestDTO) -> {
        if (!Objects.isNull(adminRepository.getAdminByUsername(requestDTO.getUsername()))) ;
        throw new DataDuplicationException("Admin username already exits", "Admin username already exits");

            /*SIMILARLY FOR EMAIL ADDRESS*/
    };

I want to refactor the existing code so that the multiple loops could be reduced.

abc abc@f1soft.com , xyz xyz@f1soft.com -> allowed

abc abc@f1soft.com, abc xyz@f1soft.com -> not allowed

abc abc@f1soft.com, xyz abc@f1soft.com -> not allowed

(first is username and second is email address)