Java 带有Hibernate多个联接查询的ClassCastException

我有两个实体，奖励和用户，它们是相关的

manytomy

，如下所示：

public class Reward {
    @Id
    @Column(name="reward_id")
    private long rewardId;
    @ManyToMany(mappedBy="favourite")
    @LazyCollection(LazyCollectionOption.FALSE)
    private Collection<User> favouriteUsers;
}

问题是，当我运行此查询并将查询结果等同于键入

奖励

时，我得到以下异常：

java.lang.ClassCastException: [Ljava.lang.Object; cannot be cast to com.xxxxxxx.model.Reward
    at com.xxxxxxx.sevice.RewardService.addFavourite(RewardService.java:26)
    at com.xxxxxxx.resources.RewardResource.addFavourite(RewardResource.java:36)
    at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
    at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:62)
    at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
    at java.lang.reflect.Method.invoke(Method.java:498)
    at org.glassfish.jersey.server.model.internal.ResourceMethodInvocationHandlerFactory$1.invoke(ResourceMethodInvocationHandlerFactory.java:81)
    at org.glassfish.jersey.server.model.internal.AbstractJavaResourceMethodDispatcher$1.run(AbstractJavaResourceMethodDispatcher.java:144)
    at org.glassfish.jersey.server.model.internal.AbstractJavaResourceMethodDispatcher.invoke(AbstractJavaResourceMethodDispatcher.java:161)
    at org.glassfish.jersey.server.model.internal.JavaResourceMethodDispatcherProvider$TypeOutInvoker.doDispatch(JavaResourceMethodDispatcherProvider.java:205)
    at org.glassfish.jersey.server.model.internal.AbstractJavaResourceMethodDispatcher.dispatch(AbstractJavaResourceMethodDispatcher.java:99)
    at org.glassfish.jersey.server.model.ResourceMethodInvoker.invoke(ResourceMethodInvoker.java:389)
    at org.glassfish.jersey.server.model.ResourceMethodInvoker.apply(ResourceMethodInvoker.java:347)
    at org.glassfish.jersey.server.model.ResourceMethodInvoker.apply(ResourceMethodInvoker.java:102)
    at org.glassfish.jersey.server.ServerRuntime$2.run(ServerRuntime.java:326)
    at org.glassfish.jersey.internal.Errors$1.call(Errors.java:271)
    at org.glassfish.jersey.internal.Errors$1.call(Errors.java:267)
    at org.glassfish.jersey.internal.Errors.process(Errors.java:315)
    at org.glassfish.jersey.internal.Errors.process(Errors.java:297)
    at org.glassfish.jersey.internal.Errors.process(Errors.java:267)
    at org.glassfish.jersey.process.internal.RequestScope.runInScope(RequestScope.java:317)
    at org.glassfish.jersey.server.ServerRuntime.process(ServerRuntime.java:305)
    at org.glassfish.jersey.server.ApplicationHandler.handle(ApplicationHandler.java:1154)
    at org.glassfish.jersey.servlet.WebComponent.serviceImpl(WebComponent.java:473)
    at org.glassfish.jersey.servlet.WebComponent.service(WebComponent.java:427)
    at org.glassfish.jersey.servlet.ServletContainer.service(ServletContainer.java:388)
    at org.glassfish.jersey.servlet.ServletContainer.service(ServletContainer.java:341)
    at org.glassfish.jersey.servlet.ServletContainer.service(ServletContainer.java:228)
    at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:231)
    at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:166)
    at org.apache.tomcat.websocket.server.WsFilter.doFilter(WsFilter.java:52)
    at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:193)
    at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:166)
    at org.apache.catalina.core.StandardWrapperValve.invoke(StandardWrapperValve.java:198)
    at org.apache.catalina.core.StandardContextValve.invoke(StandardContextValve.java:96)
    at org.apache.catalina.authenticator.AuthenticatorBase.invoke(AuthenticatorBase.java:478)
    at org.apache.catalina.core.StandardHostValve.invoke(StandardHostValve.java:140)
    at org.apache.catalina.valves.ErrorReportValve.invoke(ErrorReportValve.java:80)
    at org.apache.catalina.valves.AbstractAccessLogValve.invoke(AbstractAccessLogValve.java:624)
    at org.apache.catalina.core.StandardEngineValve.invoke(StandardEngineValve.java:87)
    at org.apache.catalina.connector.CoyoteAdapter.service(CoyoteAdapter.java:342)
    at org.apache.coyote.http11.Http11Processor.service(Http11Processor.java:799)
    at org.apache.coyote.AbstractProcessorLight.process(AbstractProcessorLight.java:66)
    at org.apache.coyote.AbstractProtocol$ConnectionHandler.process(AbstractProtocol.java:861)
    at org.apache.tomcat.util.net.NioEndpoint$SocketProcessor.doRun(NioEndpoint.java:1455)
    at org.apache.tomcat.util.net.SocketProcessorBase.run(SocketProcessorBase.java:49)
    at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1142)
    at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:617)
    at org.apache.tomcat.util.threads.TaskThread$WrappingRunnable.run(TaskThread.java:61)
    at java.lang.Thread.run(Thread.java:748)

此查询的hibernate查询日志如下：

Hibernate: select favouriteu0_.favourite_id as favourit2_3_0_, favouriteu0_.user_id as user_id1_3_0_, user1_.user_id as user_id1_2_1_ from FAVOURITE favouriteu0_ inner join USER user1_ on favouriteu0_.user_id=user1_.user_id where favouriteu0_.favourite_id=?

我想不出这个错误。有人能帮忙吗

编辑：我执行查询的部分是：

public Reward addFavourite(long userId, Reward favouriteReward) {
        Object<Reward> rewardObject = new ObjectImpl<Reward>();
        long favouriteId = favouriteReward.getRewardId();
        // Check if favourited before. 
        // Below is the line that throws the exception.
        Reward checkReward = rewardObject.getObjectByNamedQueryLongLong("Favourite.byUserAndReward", userId, favouriteId)
        if (checkReward != null) {
            return favouriteReward;
        }
}

公共奖励addFavorite（长用户ID，奖励Favorite奖励）{
Object rewardObject=new ObjectImpl（）；
long-favoriteId=favoriteReward.getRewardId（）；
//检查之前是否喜欢。
//下面是引发异常的行。
奖励检查奖励=rewardObject.GetObjectByNamedQueryLong（“Favorite.ByUserAndWard”，用户ID，FavoriteID）
if（checkReward！=null）{
回报优待奖励；
}
}

[Ljava.lang.Object

表示您的查询返回对象的数组，您试图将其强制转换为对象

更新： 由于您在不使用

SELECT

子句的情况下进行查询，并加入

User

，Hibernate将返回

奖励

和

用户

对象，这就是您获得

对象[]

的原因。我可以想出两个解决方法

您可以在

SELECT

子句中提到要获取的对象，如

从奖励r中选择r加入r.FavoriteUsers u，其中u.userId=？和r.rewardId=？

或者，您可以在查询中使用

fetch

，如

from Reward r join fetch r.favoriteUsers u，其中u.userId=？和r.rewardId=？

---

你能把代码贴在执行代码的地方吗query@wolverine我添加了代码的一部分。您发布的查询日志似乎不完整。这是唯一执行的查询吗？它甚至不是从奖励表中进行查询，但在查询的定义中，我具体执行了

object=（T）query.uniqueResult（）；

谢谢，使用了您提到的选项1。

Hibernate: select favouriteu0_.favourite_id as favourit2_3_0_, favouriteu0_.user_id as user_id1_3_0_, user1_.user_id as user_id1_2_1_ from FAVOURITE favouriteu0_ inner join USER user1_ on favouriteu0_.user_id=user1_.user_id where favouriteu0_.favourite_id=?

public Reward addFavourite(long userId, Reward favouriteReward) {
        Object<Reward> rewardObject = new ObjectImpl<Reward>();
        long favouriteId = favouriteReward.getRewardId();
        // Check if favourited before. 
        // Below is the line that throws the exception.
        Reward checkReward = rewardObject.getObjectByNamedQueryLongLong("Favourite.byUserAndReward", userId, favouriteId)
        if (checkReward != null) {
            return favouriteReward;
        }
}