Question

以下代码为我提供了org.hibernate.HibernateException: The internal connection pool has reached its maximum size and no connection is currently available!. 此错误表明我没有关闭事务，因为我将connection pool大小设置为20，所以在消耗所有连接时会出错。以下是代码：

public class XxspAsnOutHeaderRepo {
public static Logger logger = Logger.getLogger(XxspAsnOutHeaderRepo.class);

private EntityManager entityManager = JPAUtil.getEntityManagerFactory().createEntityManager();
private EntityTransaction transaction = entityManager.getTransaction();

public List<XxspAsnOutHeaderEntity> getOneOutHeaderWithFlag(String flag) {
    TypedQuery<XxspAsnOutHeaderEntity> query = null;
    try {
        if (!transaction.isActive())
            transaction.begin();
        logger.info("getting headers from Database..... ");
        query = entityManager.createNamedQuery(XxspAsnOutHeaderEntity.FIND_ALL_HEADERS_FLAG_SIX, XxspAsnOutHeaderEntity.class)
                                .setParameter("proc_flag", flag).setMaxResults(1);

    } catch (PersistenceException ex) {
        logger.error("Error occured while fetching data from DataBase...\n", ex);
        throw ex;
    } finally {
        if (transaction.getRollbackOnly())
            transaction.rollback();         
    }
    return query.getResultList(); 

  }
}

测试用例：

 @Test    
 public void testConnectionPoolLimit(){
      for(int i=1; i<30; i++){
          new XxspAsnOutHeaderRepo().getOneOutHeaderWithFlag("6");
      }
 }

上述代码在20 select个语句后失败。但是当我删除if (!transaction.isActive()) transaction.begin();时，代码运行正常并创建了30个读取操作。而这一次提高了速度如果我最后写transaction.commit();语句，上面也会运行。但表现很慢。

Read操作不需要交易吗？

为什么Read操作不需要JPA中的Transaction？

0 个答案: