用空对象替换SQL异常

Question

我使用此SQL查询来获取简单对象：

@Override
    public Optional<PaymentTransactions> paymentTransactionByWpfPaymentId(Integer id) {
        String hql = "SELECT t FROM " + PaymentTransactions.class.getName() + " t " 
                + " WHERE wppt.wpf_payment_id = :id ";
        TypedQuery<PaymentTransactions> query = entityManager.createQuery(hql, PaymentTransactions.class).setParameter("id", id);
        List<PaymentTransactions> wpfPayments = query.getResultList();
        return wpfPayments.isEmpty() ? Optional.empty() : Optional.of(wpfPayments.get(0));
    }

我用这个终点

@GetMapping("/{id}")
    public ResponseEntity<List<PaymentTransactionsDTO>> getWpf_reference_transactions(@PathVariable String id) throws NumberFormatException, Exception {

        Optional<PaymentTransactions> tnx = wpfPaymentsService.paymentTransactionByWpfPaymentId(Integer.parseInt(id));

        if(tnx.get().getId() != 0) {
            return ResponseEntity.ok(transactionService
                    .get(Integer.valueOf(tnx.get().getId())).stream()
                    .collect(Collectors.toList()));
        } 

        return ResponseEntity.notFound().build();
    }

但是当数据库为空时我会得到java.util.NoSuchElementException: No value present。有没有办法只返回空对象没有这个异常？

Answer 1

Optional.get()将抛出NoSuchElementException - if there is no value present，所以使用isPresent知道值是否存在于可选或不存在

if(tnx.isPresent() && tnx.get().getId() != 0) {
        return ResponseEntity.ok(transactionService
                .get(Integer.valueOf(tnx.get().getId())).stream()
                .collect(Collectors.toList()));
    } 

    return ResponseEntity.notFound().build();

Answer 2

您可以使用简化返回语句

return tnx.map(PaymentTransactions::getId)
          .filter(id -> id != 0)
          .map(id -> transactionService.get(id)
                                       .stream()
                                       .collect(Collectors.toList()))
          .map(ResponseEntity::ok)
          .orElse(ResponseEntity.notFound().build());

为了更清洁的方法。

还有，这个

id -> transactionService.get(id)
                        .stream()
                        .collect(Collectors.toList()

可以变成

id -> new ArrayList<>(transactionService.get(id)))

所以你有

tnx.map(Transaction::getId)
   .filter(id -> id != 0)
   .map(id -> new ArrayList<>(transactionService.get(id)))
   .map(ResponseEntity::ok)
   .orElse(ResponseEntity.notFound().build());

我也怀疑你需要

id -> new ArrayList<>(transactionService.get(id))

相反，这就足够了

id -> transactionService.get(id)

因为你根本无法接触那个List。

Answer 3

是。无论您的异常源自何处，请将其包装在try/catch块中，如下所示：

try {
    <code that throws exception>
} catch (NoSuchElementException e) {
    return new MyObject();
}