JPQL会话bean引起的java.lang.ClassCastException

Question

我正在尝试创建一个包含JPQL的远程服务，但对于最简单的查询却出现此错误。

在我的身份验证服务中：

@Override
public Users checkDatabase(String email) {
    Query query = entityManager.createQuery("SELECT u from Users u WHERE u.nom = :email", Users.class)
            .setParameter("email", email);
    Users user = (Users) query.getSingleResult();
    return user;
}

我的客户代码如下：

String jndiName = "Petroca-ear/Petroca-ejb/AuthenticationServices!com.esprit.services.AuthenticationServicesRemote";
Context context = new InitialContext();
AuthenticationServicesRemote proxy = (AuthenticationServicesRemote) context.lookup(jndiName);
System.out.println(proxy.checkEmail("test@s"));
Users user = (Users) proxy.checkDatabase("peter");

执行此操作时，出现此错误：

false
Exception in thread "main" java.lang.ClassCastException: java.lang.Class cannot be cast to java.lang.String
    at org.jboss.ejb.client.remoting.ProtocolMessageHandler.readAttachments(ProtocolMessageHandler.java:55)
    at org.jboss.ejb.client.remoting.InvocationExceptionResponseHandler$MethodInvocationExceptionResultProducer.getResult(InvocationExceptionResponseHandler.java:82)
    at org.jboss.ejb.client.EJBClientInvocationContext.getResult(EJBClientInvocationContext.java:276)
    at org.jboss.ejb.client.EJBObjectInterceptor.handleInvocationResult(EJBObjectInterceptor.java:64)
    at org.jboss.ejb.client.EJBClientInvocationContext.getResult(EJBClientInvocationContext.java:290)
    at org.jboss.ejb.client.EJBHomeInterceptor.handleInvocationResult(EJBHomeInterceptor.java:88)
    at org.jboss.ejb.client.EJBClientInvocationContext.getResult(EJBClientInvocationContext.java:290)
    at org.jboss.ejb.client.TransactionInterceptor.handleInvocationResult(TransactionInterceptor.java:46)
    at org.jboss.ejb.client.EJBClientInvocationContext.getResult(EJBClientInvocationContext.java:290)
    at org.jboss.ejb.client.ReceiverInterceptor.handleInvocationResult(ReceiverInterceptor.java:129)
    at org.jboss.ejb.client.EJBClientInvocationContext.getResult(EJBClientInvocationContext.java:265)
    at org.jboss.ejb.client.EJBClientInvocationContext.awaitResponse(EJBClientInvocationContext.java:453)
    at org.jboss.ejb.client.EJBInvocationHandler.doInvoke(EJBInvocationHandler.java:202)
    at org.jboss.ejb.client.EJBInvocationHandler.doInvoke(EJBInvocationHandler.java:181)
    at org.jboss.ejb.client.EJBInvocationHandler.invoke(EJBInvocationHandler.java:144)
    at com.sun.proxy.$Proxy2.checkDatabase(Unknown Source)
    at TEST.testPetroca.main(testPetroca.java:23)