Question

我使用此SQL查询获取简单对象：

@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));
    }

我使用此终点

@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，我得到java.util.NoSuchElementException: No value present。有没有一种方法可以只返回没有该异常的空对象？

Answer 1

您可以使用以下方式简化return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());

一种更清洁的方法。

也是这个

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

可以成为

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，这足够了

id -> transactionService.get(id)

因为您根本无法触摸List。

Answer 2

Optional.get()将抛出NoSuchElementException - if there is no value present，因此请使用isPresent来知道该值是否为可选值

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 3

是的。无论异常来自何处，都将其包装在try/catch块中，如下所示：

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

用空对象替换SQL异常

3 个答案: