java.lang.ClassCastException：[B 无法转换为 [Ljava.lang.Object；在使用 JPA 2.2 query.getResultStream().findFirst() 时

Question

我的Spring数据存储方法的代码如下：

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. 运行时出现以下异常：

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，在此先感谢您的回答。

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

字节没有原始流，您可以在调试器中检查您获得的流类型可能 Stream<Byte[]> 或 Stream<Object[]>。这可以解释您遇到的异常。使用 Byte[] 应该可以解决您的问题。

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();

}

Answer 2

先用 getResultList 试一下，看看是否可行：

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，select N 条记录只取第一个使用 fidFirst 是低效的。如果这个查询 returns 100 条记录怎么办？您仍然 select 数据库中的全部 100。

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 看看它为什么不起作用 return byte[].

java.lang.ClassCastException：[B 无法转换为 [Ljava.lang.Object；在使用 JPA 2.2 query.getResultStream().findFirst() 时

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

java

spring-data-jpa

hibernate-5.x

jpa-2.2