@GetMapping
@PreAuthorize("hasRole('CLIENT')")
public List<AccountListResponse> accountList(@CurrentUser UserPrincipal userPrincipal) {
    List<AccountListResponse> accountList = new ArrayList<>();
    accountRepo.findAllByClient_User_Id(userPrincipal.getId())
            .forEach(account ->
                    accountList.add(new AccountListResponse(
                            account.getUniqCheckId(),
                            account.getSum(),
                            account.getUpdatedAt(),
                            account.getCurrencyName().getName(),
                            account.getTypeAccount().getType())
                    )
            );
    return accountList;
}

@Data
public class AccountListResponse {
private String accountId;
private BigDecimal sum;
private LocalDateTime updatedAt;
private CurrencyName currency;
private TypeAccountName type;

public AccountListResponse(String accountId,
                           BigDecimal sum,
                           LocalDateTime updatedAt,
                           CurrencyName currency,
                           TypeAccountName type) {
    this.accountId = accountId;
    this.sum = sum;
    this.updatedAt = updatedAt;
    this.currency = currency;
    this.type = type;
  }
}

{
    "accountId": "804cd3da-7865-45b2-bf48-1cb471cb4484",
    "sum": 480,
    "updatedAt": "2018-10-15T09:40:26.302",
    "currency": "RUB",
    "type": "DEBIT"
},
{
    "accountId": "6e388506-04f6-410a-b63f-e3e7e9d24693",
    "sum": 0,
    "updatedAt": "2018-10-15T14:12:15.491",
    "currency": "EUR",
    "type": "DEBIT"
},
{
    "accountId": "bec1cb7c-8543-452d-bf3c-329b0e268468",
    "sum": 0,
    "updatedAt": "2018-10-15T14:12:22.591",
    "currency": "USD",
    "type": "DEBIT"
}