java.lang.ClassCastException : [B cannot be cast to [Ljava. lang.Object;使用 JPA 2.2 query.getResultStream().findFirst() 时

Question

我的Spring Data存储库方法的代码如下:

public Optional<byte[]> findShipmentLabelByClientIdAndAwb(String clientId, String awb) {

    String queryString = "select g.shipmentLabel as shipmentLabel from GenericShipment g where g.client.id = :clientId and g.shipmentId = :awb " +
        " AND (g.processingStatus is null or g.processingStatus <> 'DELETED') AND g.shipmentLabel is not null";

    val query = entityManager.createQuery(queryString, byte[].class);

    query.setParameter("clientId", clientId);
    query.setParameter("awb", awb);

    return query.getResultStream().findFirst();

}

如您所见，我正在尝试以字节数组的形式获取 shipmentLabel 列，该列在我的 Postgres 架构中定义为 bytea。 运行时出现如下异常:

java.lang.ClassCastException: [B cannot be cast to [Ljava.lang.Object; at org.hibernate.internal.ScrollableResultsImpl.prepareCurrentRow(ScrollableResultsImpl.java:203) at org.hibernate.internal.ScrollableResultsImpl.next(ScrollableResultsImpl.java:101) at org.hibernate.query.internal.ScrollableResultsIterator.hasNext(ScrollableResultsIterator.java:33) at java.util.Spliterators$IteratorSpliterator.tryAdvance(Spliterators.java:1811) at java.util.stream.ReferencePipeline.forEachWithCancel(ReferencePipeline.java:126) at java.util.stream.AbstractPipeline.copyIntoWithCancel(AbstractPipeline.java:499) at java.util.stream.AbstractPipeline.copyInto(AbstractPipeline.java:486) at java.util.stream.AbstractPipeline.wrapAndCopyInto(AbstractPipeline.java:472) at java.util.stream.FindOps$FindOp.evaluateSequential(FindOps.java:152) at java.util.stream.AbstractPipeline.evaluate(AbstractPipeline.java:234) at java.util.stream.ReferencePipeline.findFirst(ReferencePipeline.java:531) at org.hibernate.query.spi.StreamDecorator.findFirst(StreamDecorator.java:260)

我想知道这是否是这里的预期行为，提前感谢您的回答。

目前，解决方法是使用 JPA 2.1 变体:

return query.getResultList().stream().findFirst();

作为环境，我使用的是Spring Boot 2.3.3，Hibernate版本是5.4.20。

Answer 1

首先尝试使用getResultList，看看它是否有效:

public Optional<Byte[]> findShipmentLabelByClientIdAndAwb(
        String clientId, String awb) {
    return entityManager.createQuery("""
        select 
            g.shipmentLabel as shipmentLabel 
        from GenericShipment g 
        where 
            g.client.id = :clientId and 
            g.shipmentId = :awb and 
            (
                g.processingStatus is null or 
                g.processingStatus <> 'DELETED'
            ) and 
            g.shipmentLabel is not null
        """)
    .setParameter("clientId", clientId)
    .setParameter("awb", awb)
    .setMaxResults(1)
    .getResultList()
    .stream()
    .findFirst();
}

请注意，使用 fidFirst 选择 N 条记录仅获取第一条记录的效率很低。如果此查询返回 100 条记录怎么办？您仍然需要从数据库中选择全部 100 个。

这就是我添加 setMaxResults 调用的原因。

如果这不起作用，请尝试调试 Hibernate BinaryType 并查看为什么它不返回 byte[]。