package bigbank; import org.springframework.util.Assert; public class BankServiceImpl implements BankService { private final BankDao bankDao; public BankServiceImpl(BankDao bankDao) { Assert.notNull(bankDao); this.bankDao = bankDao; } public Account[] findAccounts() { return this.bankDao.findAccounts(); } public Account post(Account account, double amount) { Assert.notNull(account); // We read account back from DAO so it reflects the latest balance Account a = bankDao.readAccount(account.getId()); if (a == null) { throw new IllegalArgumentException("Couldn't find requested account"); } a.setBalance(a.getBalance() + amount); bankDao.createOrUpdateAccount(a); return a; } public Account readAccount(Long id) { return bankDao.readAccount(id); } }