Repository

定义一个根据类型查询考题的接口

@Repository
public interface ExamQuestionDao extends JpaRepository<ExamQuestion, Integer> {
    /**
     * 根据考题类型查询考题
     *
     * @param questionType {@link com.lixin.newworld.domain.enums.QuestionType} 考题类型
     * @return {@link List<ExamQuestion>} 考题
     */
    Stream<ExamQuestion> findAllByType(QuestionType questionType);
}

Client

简单写了一个单元测试来调用

@SpringBootTest(webEnvironment = SpringBootTest.WebEnvironment.NONE)
public class ExamQuestionDaoTests {
    @Autowired
    private ExamQuestionDao examQuestionDao;
    @Test
    public void testJPA() {
        long count = examQuestionDao.findAllByType(QuestionType.JUDGE)
                .filter(q -> q.getType() != QuestionType.JUDGE)
                .count();
        assert count == 0;
    }
}

Error

Duang，翻车了！抛出以下异常👇

org.springframework.dao.InvalidDataAccessApiUsageException: You’re trying to execute a streaming query method without a surrounding transaction that keeps the connection open so that the Stream can actually be consumed. Make sure the code consuming the stream uses @Transactional or any other way of declaring a (read-only) transaction.

报错原因是：为了保持 Stream 连接打开，必须保证消费 Stream 的代码处于事务控制！

Fix

根据报错的提示，需要在消费 Stream 代码处添加 @Transactional 注解即可解决上述报错！最终无误代码如下

@SpringBootTest(webEnvironment = SpringBootTest.WebEnvironment.NONE)
public class ExamQuestionDaoTests {
    @Autowired
    private ExamQuestionDao examQuestionDao;
    @Test
    @Transactional(readOnly = true)
    public void testJPA() {
        long count = examQuestionDao.findAllByType(QuestionType.JUDGE)
                .filter(q -> q.getType() != QuestionType.JUDGE)
                .count();
        assert count == 0;
    }
}

再执行一次，测试通过，可以开始愉快的玩耍 Stream API 了！