Example of service with many dependencies

DepositService.kt

@Service
class DepositService(
	val userRepo: UserRepository,
	val userAccountRepo: UserAccountRepository,
	val exchangeApiClient: ExchangeApiClient,
	val eventBus: EventBus
) {
  @Transactional
  fun deposit(userId: String, amount: BigDecimal, currency: String){
    require(amount > BigDecimal.ZERO) { “Amount must be larger than 0” }
    require(Currencies.isSupported(currency)) { “$currency is not supported”}
    userRepo.findById(userId)?.let { user ->
      userAccountRepo.findByAccountId(user.accountId)?.let { account ->
        val rateToUsd = if (currency != “USD”) {
	  exchangeApiClient.getRate(RateRequest(currency, “USD”)).rate
	} else { 1.0 }
	val rateToPref = if (account.currency != “USD”) {
	  exchangeApiClient.getRate(RateRequest(“USD”, account.currency)).rate
	} else { 1.0 }
	val oldBalance = account.balance
	account.balance += amount * rateToUsd.toBigDecimal() * rateToPref.toBigDecimal()
	userAccountRepo.save(account)
	val update = BalanceUpdate(
	  userId, oldBalance, account.balance
	)
	eventBus.publish(ProducerRecord(“balance-updates”, update))
      }
    }
  }
}