Java 8流嵌套ForEach与不同的条件

Question

我对Java 8流完全陌生。只是想知道如何使用Java流api编写下面的代码。不确定如何编写带过滤器的嵌套循环来映射数据。

public AccountByCustomerDto getAccountDetails(int customerId, HttpServletRequest request) throws Exception {
List<Accountowner> accountOwnerList = repo.getAccountOwners(customerId);
List<AccountByCustomerDto.AccountDto> aDtoList = new ArrayList<AccountByCustomerDto.AccountDto>();

for (Accountowner accountOwner : accountOwnerList) {        
String currency = accountOwner.getAccount1().getAccountCurrency();
if(accountOwner != null && currency.startsWith("USD")) {                
List<Accountbalance> accountBalanceList = accountOwner.getAccount1().getAccountbalances();
List<AccountByCustomerDto.BalancesDto> balanceDtoList = new ArrayList<AccountByCustomerDto.BalancesDto>();
for (Accountbalance balance : accountBalanceList) {
String creditInclude = balance.getCreditLimitIncluded();
if(balance != null && creditInclude.equals("Y")) {

AccountByCustomerDto.BalancesDto balanceDto = AccountByCustomerDto.BalancesDto.builder()
.balanceType(balance.getBalanceType()).baDto(null)                              
.referenceDate(
balance.getReferenceDate().toInstant().atZone(ZoneId.systemDefault()).toLocalDate())                                
.build();
balanceDtoList.add(balanceDto);
}                   
}
String accountId = Integer.toString(accountOwner.getAccount1().getAccountId()) + ":"
+ accountOwner.getAccount1().getAccountCurrency();
AccountByCustomerDto.AccountDto adto = AccountByCustomerDto.AccountDto.builder()
.accountId(Utility.encrypt(accountId))
.accountNumberDisplay(accountOwner.getAccount1().getAccountDisplay())
.balances(balanceDtoList).accountLink(null).build();
aDtoList.add(adto);
}           
}
return AccountByCustomerDto.builder().accounts(aDtoList).build();
}

Answer 1

我认为仅仅将代码切换到Stream将使代码更不容易阅读。当一个方法变得很长时最好把它分成更小的方法。当代码被分割成更小的方法流时，与传统循环相比，在可读性方面提供了真正的好处。

如果accountOwnerCurrencyIsUSD

为真，流中的元素保持在流中。剩余的元素使用createAccountDto映射到AccountDto，结果被收集到AccountDto列表中。比创建列表，循环遍历其他列表，获取货币，检查货币，创建另一个列表…

public AccountByCustomerDto getAccountDetails(int customerId, HttpServletRequest request) throws Exception {    
List<AccountByCustomerDto.AccountDto> aDtoList = accountOwnerList.stream()
.filter(this::accountOwnerCurrencyIsUSD)
.map(this::createAccountDto)
.collect(Collectors.toList());
return AccountByCustomerDto.builder().accounts(aDtoList).build();
}
private AccountCustomerDto.AccountDto createAccountDto(Accountowner owner) {
String accountId = accountOwner.getAccount1().getAccountId() + ":" + accountOwner.getAccount1().getAccountCurrency();
List<AccountByCustomerDto.BalancesDto> balanceDtoList = accountOwner.getAccount1().getAccountbalances()
.stream()
.filter(this::includesCredit)
.map(this::createBalanceDto)
.collect(Collectors.toList());
return AccountByCustomerDto.AccountDto.builder()
.accountId(Utility.encrypt(accountId))         
.accountNumberDisplay(accountOwner.getAccount1().getAccountDisplay())
.balances(balanceDtoList)
.accountLink(null)
.build();
}
private AccountByCustomerDto.BalancesDto createBalanceDto(Accountbalance balance) {
return AccountByCustomerDto.BalancesDto.builder()
.balanceType(balance.getBalanceType())
.baDto(null)
.referenceDate(alance.getReferenceDate().toInstant().atZone(ZoneId.systemDefault()).toLocalDate())
.build();
}
private boolean accountOwnerCurrencyIsUSD(Accountowner owner) {
return accountOwner != null && "USD".eqauls(accountOwner.getAccount1().getAccountCurrency());
}
private boolean includesCredit(Accountbalance balance) {
return balance != null && "Y".equals(balance.getCreditLimitIncluded());
}

我没有测试代码的方法，所以对它持保留态度。