我正在为和GlassFish 4创建一个JSF+JPA项目。有几次我在这里遇到了一个异常：
List<User> users = connection.getUserList();
for (User u : users) { //exception
public List<User> getUserList() {
EntityManager em = Persistence.createEntityManagerFactory("project").createEntityManager();
List<User> users = em.createQuery("SELECT c FROM User c", User.class).getResultList();
em.close();
return users;
}
堆栈跟踪：
javax.faces.el.EvaluationException: java.lang.ClassCastException: de.sep.ateam.sap.norris.model.User cannot be cast to de.sep.ateam.sap.norris.model.User
at javax.faces.component.MethodBindingMethodExpressionAdapter.invoke(MethodBindingMethodExpressionAdapter.java:101)
at com.sun.faces.application.ActionListenerImpl.processAction(ActionListenerImpl.java:102)
at javax.faces.component.UICommand.broadcast(UICommand.java:315)
at javax.faces.component.UIViewRoot.broadcastEvents(UIViewRoot.java:790)
at javax.faces.component.UIViewRoot.processApplication(UIViewRoot.java:1282)
at com.sun.faces.lifecycle.InvokeApplicationPhase.execute(InvokeApplicationPhase.java:81)
at com.sun.faces.lifecycle.Phase.doPhase(Phase.java:101)
at com.sun.faces.lifecycle.LifecycleImpl.execute(LifecycleImpl.java:198)
at javax.faces.webapp.FacesServlet.service(FacesServlet.java:646)
at org.apache.catalina.core.StandardWrapper.service(StandardWrapper.java:1682)
at org.apache.catalina.core.StandardWrapperValve.invoke(StandardWrapperValve.java:318)
at org.apache.catalina.core.StandardContextValve.invoke(StandardContextValve.java:160)
at org.apache.catalina.core.StandardPipeline.doInvoke(StandardPipeline.java:734)
at org.apache.catalina.core.StandardPipeline.invoke(StandardPipeline.java:673)
at com.sun.enterprise.web.WebPipeline.invoke(WebPipeline.java:99)
at org.apache.catalina.core.StandardHostValve.invoke(StandardHostValve.java:174)
at org.apache.catalina.connector.CoyoteAdapter.doService(CoyoteAdapter.java:357)
at org.apache.catalina.connector.CoyoteAdapter.service(CoyoteAdapter.java:260)
at com.sun.enterprise.v3.services.impl.ContainerMapper.service(ContainerMapper.java:188)
at org.glassfish.grizzly.http.server.HttpHandler.runService(HttpHandler.java:191)
at org.glassfish.grizzly.http.server.HttpHandler.doHandle(HttpHandler.java:168)
at org.glassfish.grizzly.http.server.HttpServerFilter.handleRead(HttpServerFilter.java:189)
at org.glassfish.grizzly.filterchain.ExecutorResolver$9.execute(ExecutorResolver.java:119)
at org.glassfish.grizzly.filterchain.DefaultFilterChain.executeFilter(DefaultFilterChain.java:288)
at org.glassfish.grizzly.filterchain.DefaultFilterChain.executeChainPart(DefaultFilterChain.java:206)
at org.glassfish.grizzly.filterchain.DefaultFilterChain.execute(DefaultFilterChain.java:136)
at org.glassfish.grizzly.filterchain.DefaultFilterChain.process(DefaultFilterChain.java:114)
at org.glassfish.grizzly.ProcessorExecutor.execute(ProcessorExecutor.java:77)
at org.glassfish.grizzly.nio.transport.TCPNIOTransport.fireIOEvent(TCPNIOTransport.java:838)
at org.glassfish.grizzly.strategies.AbstractIOStrategy.fireIOEvent(AbstractIOStrategy.java:113)
at org.glassfish.grizzly.strategies.WorkerThreadIOStrategy.run0(WorkerThreadIOStrategy.java:115)
at org.glassfish.grizzly.strategies.WorkerThreadIOStrategy.access$100(WorkerThreadIOStrategy.java:55)
at org.glassfish.grizzly.strategies.WorkerThreadIOStrategy$WorkerThreadRunnable.run(WorkerThreadIOStrategy.java:135)
at org.glassfish.grizzly.threadpool.AbstractThreadPool$Worker.doWork(AbstractThreadPool.java:564)
at org.glassfish.grizzly.threadpool.AbstractThreadPool$Worker.run(AbstractThreadPool.java:544)
at java.lang.Thread.run(Thread.java:744)
Caused by: java.lang.ClassCastException: de.sep.ateam.sap.norris.model.User cannot be cast to de.sep.ateam.sap.norris.model.User
at de.sep.ateam.sap.norris.controller.beans.LoginBean.doLogin(LoginBean.java:50)
at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:57)
at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
at java.lang.reflect.Method.invoke(Method.java:606)
at javax.el.ELUtil.invokeMethod(ELUtil.java:326)
at javax.el.BeanELResolver.invoke(BeanELResolver.java:536)
at javax.el.CompositeELResolver.invoke(CompositeELResolver.java:256)
at com.sun.el.parser.AstValue.invoke(AstValue.java:269)
at com.sun.el.MethodExpressionImpl.invoke(MethodExpressionImpl.java:304)
at org.jboss.weld.util.el.ForwardingMethodExpression.invoke(ForwardingMethodExpression.java:40)
at org.jboss.weld.el.WeldMethodExpression.invoke(WeldMethodExpression.java:50)
at com.sun.faces.facelets.el.TagMethodExpression.invoke(TagMethodExpression.java:105)
at javax.faces.component.MethodBindingMethodExpressionAdapter.invoke(MethodBindingMethodExpressionAdapter.java:87)
... 35 more
如果确定应用程序服务器中没有加载同一类的多个版本，则可以尝试重置服务器缓存。
遵循以下步骤：
- 取消部署应用程序
- 停止应用程序服务器
- 删除应用程序服务器的osgi缓存文件夹。也就是说，如果你是使用glassfish，它是文件夹：E： \glassfish-3.1.2.2\glassfish\domains\domain1\osgi缓存
- 重新启动服务器
- 部署应用程序
我遇到了同样的问题，我终于在java.net上找到了一个解决方法：
将所有org.eclipse.persistence jar files从glassfish4/glassfish/modules复制到WEB-INF/lib。然后进入glassfish-web.xml，并将class-delegate设置为false。
为我工作！
我也遇到了类似的问题，因为我正在序列化类，并且在类更新后无法反序列化序列化版本，并且在没有重新启动容器的情况下重新启动了应用程序。
通常，当同一jar的多个实例位于不同的类加载器中时，就会发生这种情况。大多数应用程序服务器都有一个全局类加载器和一个特定于web应用程序的类加载器（有些也有其他类加载器，如contrib等）。如果食物链中更高层的类加载器已经定义了该类，并且它被较低级别的类加载器重新定义，则可能会出现这种情况（不同类加载器中的同一类被认为是不同的，即使它的定义是相同的）。不能保证如何/何时加载jar的顺序，这可以解释为什么你有时会看到错误，有时却没有。长话短说，请确保您尚未在服务器中web应用程序可见的其他位置部署包含此类的jar。