java将对象数组转换为JPA实体数组？

Question

每次我试图从我从jpa调用中提取的实体列表中获取实体数组时，我都会得到一个强制转换异常。例如

QuickLaunch[] qLaunchArr = null;
List<QuickLaunch> listQL = null;
try
{
    System.out.println("testing 1..2..3");

    //qLaunchArr
    listQL = emf.createNamedQuery("getQuickLaunch").getResultList();
    Object[] objArr = listQL.toArray();
    //System.out.println(listQL.size());
    qLaunchArr = (QuickLaunch[]) listQL.toArray();       
}
catch (Exception e)
{
    System.out.println("Bull Hockey!!!! I can't believe it's not butter!: "+e.toString());
}

[Ljava.lang.Object; incompatible with [Lcom.upmc.esdm.messaging.entities.QuickLaunch;

那是在我的服务器日志中。。。（我正在使用WID） 我也得到了这个例外

commonj.connector.runtime.DataHandlerException: CWLAP0507E: The response bean class for java class  method GetAllQuickLaunchComponents cannot be created. Reason java.lang.IllegalArgumentException: argument type mismatch.

Answer 1

您可以尝试TypedQuery获取实体列表，而无需显式强制转换&；防止例外

TypedQuery<QuickLaunch> listQL = em.createNamedQuery("QuickLaunch.getQuickLaunch", QuickLaunch.class);

List<QuickLaunch> products = listQL .getResultList();

此外，还更改了查询名称，以便以更有意义的方式标识其类或结果类型

Answer 2

这与JPA无关，而是与Java有关，因为它不会将Object[]强制转换为QuickLaunch[]。不能使用对象数组而不是QuickLaunch[]数组吗

Answer 3

好吧。。。我想我找到了答案。它的灵感来自于这篇文章

https://stackoverflow.com/a/8060077/729820

我基本上是这样做的

try
    {
        System.out.println("testing 1..2..3");
        listQL = emf.createNamedQuery("getQuickLaunch").getResultList();
        System.out.println("What is the size of this list: number "+listQL.size());
        qLaunchArr = listQL.toArray(new QuickLaunch[listQL.size()]);         
    }

所有的例外似乎都很清楚。 谢谢你们的帮助