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我对Java EE应用程序开发非常新颖。我从here创建了示例Java EE（JPA）应用程序。javax.ejb.EJBException在运行具有GLassfish的Java EE（JPA）应用程序时
当我尝试运行该应用程序我得到以下异常： -
这是张贴在这里，但它们都没有工作对我来说类似问题的2017-08-24T13:46:01.363+0200|Warnung: StandardWrapperValve[GuestServlet]: Servlet.service() for servlet GuestServlet threw exception
javax.ejb.EJBException
at com.sun.ejb.containers.EJBContainerTransactionManager.processSystemException(EJBContainerTransactionManager.java:752)
at com.sun.ejb.containers.EJBContainerTransactionManager.completeNewTx(EJBContainerTransactionManager.java:702)
at com.sun.ejb.containers.EJBContainerTransactionManager.postInvokeTx(EJBContainerTransactionManager.java:507)
at com.sun.ejb.containers.BaseContainer.postInvokeTx(BaseContainer.java:4566)
at com.sun.ejb.containers.BaseContainer.postInvoke(BaseContainer.java:2074)
at com.sun.ejb.containers.BaseContainer.postInvoke(BaseContainer.java:2044)
at com.sun.ejb.containers.EJBLocalObjectInvocationHandler.invoke(EJBLocalObjectInvocationHandler.java:220)
at com.sun.ejb.containers.EJBLocalObjectInvocationHandlerDelegate.invoke(EJBLocalObjectInvocationHandlerDelegate.java:88)
at com.sun.proxy.$Proxy252.persist(Unknown Source)
at guest.__EJB31_Generated__GuestDao__Intf____Bean__.persist(Unknown Source)
at guest.GuestServlet.doPost(GuestServlet.java:36)
at javax.servlet.http.HttpServlet.service(HttpServlet.java:707)
at javax.servlet.http.HttpServlet.service(HttpServlet.java:790)
at org.apache.catalina.core.StandardWrapper.service(StandardWrapper.java:1682)
at org.apache.catalina.core.StandardWrapperValve.invoke(StandardWrapperValve.java:318)
at org.apache.catalina.core.StandardContextValve.invoke(StandardContextValve.java:160)
at org.apache.catalina.core.StandardPipeline.doInvoke(StandardPipeline.java:734)
at org.apache.catalina.core.StandardPipeline.invoke(StandardPipeline.java:673)
at com.sun.enterprise.web.WebPipeline.invoke(WebPipeline.java:99)
at org.apache.catalina.core.StandardHostValve.invoke(StandardHostValve.java:174)
at org.apache.catalina.connector.CoyoteAdapter.doService(CoyoteAdapter.java:416)
at org.apache.catalina.connector.CoyoteAdapter.service(CoyoteAdapter.java:283)
at com.sun.enterprise.v3.services.impl.ContainerMapper$HttpHandlerCallable.call(ContainerMapper.java:459)
at com.sun.enterprise.v3.services.impl.ContainerMapper.service(ContainerMapper.java:167)
at org.glassfish.grizzly.http.server.HttpHandler.runService(HttpHandler.java:206)
at org.glassfish.grizzly.http.server.HttpHandler.doHandle(HttpHandler.java:180)
at org.glassfish.grizzly.http.server.HttpServerFilter.handleRead(HttpServerFilter.java:235)
at org.glassfish.grizzly.filterchain.ExecutorResolver$9.execute(ExecutorResolver.java:119)
at org.glassfish.grizzly.filterchain.DefaultFilterChain.executeFilter(DefaultFilterChain.java:283)
at org.glassfish.grizzly.filterchain.DefaultFilterChain.executeChainPart(DefaultFilterChain.java:200)
at org.glassfish.grizzly.filterchain.DefaultFilterChain.execute(DefaultFilterChain.java:132)
at org.glassfish.grizzly.filterchain.DefaultFilterChain.process(DefaultFilterChain.java:111)
at org.glassfish.grizzly.ProcessorExecutor.execute(ProcessorExecutor.java:77)
at org.glassfish.grizzly.nio.transport.TCPNIOTransport.fireIOEvent(TCPNIOTransport.java:536)
at org.glassfish.grizzly.strategies.AbstractIOStrategy.fireIOEvent(AbstractIOStrategy.java:112)
at org.glassfish.grizzly.strategies.WorkerThreadIOStrategy.run0(WorkerThreadIOStrategy.java:117)
at org.glassfish.grizzly.strategies.WorkerThreadIOStrategy.access$100(WorkerThreadIOStrategy.java:56)
at org.glassfish.grizzly.strategies.WorkerThreadIOStrategy$WorkerThreadRunnable.run(WorkerThreadIOStrategy.java:137)
at org.glassfish.grizzly.threadpool.AbstractThreadPool$Worker.doWork(AbstractThreadPool.java:591)
at org.glassfish.grizzly.threadpool.AbstractThreadPool$Worker.run(AbstractThreadPool.java:571)
at java.lang.Thread.run(Thread.java:748)
Caused by: java.lang.IllegalStateException: Unable to retrieve EntityManagerFactory for unitName null
at com.sun.enterprise.container.common.impl.EntityManagerWrapper.init(EntityManagerWrapper.java:138)
at com.sun.enterprise.container.common.impl.EntityManagerWrapper.doTxRequiredCheck(EntityManagerWrapper.java:158)
at com.sun.enterprise.container.common.impl.EntityManagerWrapper.doTransactionScopedTxCheck(EntityManagerWrapper.java:151)
at com.sun.enterprise.container.common.impl.EntityManagerWrapper.persist(EntityManagerWrapper.java:281)
at guest.GuestDao.persist(GuestDao.java:20)
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.ejb.security.application.EJBSecurityManager.runMethod(EJBSecurityManager.java:1081)
at org.glassfish.ejb.security.application.EJBSecurityManager.invoke(EJBSecurityManager.java:1153)
at com.sun.ejb.containers.BaseContainer.invokeBeanMethod(BaseContainer.java:4786)
at com.sun.ejb.EjbInvocation.invokeBeanMethod(EjbInvocation.java:656)
at com.sun.ejb.containers.interceptors.AroundInvokeChainImpl.invokeNext(InterceptorManager.java:822)
at com.sun.ejb.EjbInvocation.proceed(EjbInvocation.java:608)
at org.jboss.weld.ejb.AbstractEJBRequestScopeActivationInterceptor.aroundInvoke(AbstractEJBRequestScopeActivationInterceptor.java:64)
at org.jboss.weld.ejb.SessionBeanInterceptor.aroundInvoke(SessionBeanInterceptor.java:52)
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 com.sun.ejb.containers.interceptors.AroundInvokeInterceptor.intercept(InterceptorManager.java:883)
at com.sun.ejb.containers.interceptors.AroundInvokeChainImpl.invokeNext(InterceptorManager.java:822)
at com.sun.ejb.EjbInvocation.proceed(EjbInvocation.java:608)
at com.sun.ejb.containers.interceptors.SystemInterceptorProxy.doCall(SystemInterceptorProxy.java:163)
at com.sun.ejb.containers.interceptors.SystemInterceptorProxy.aroundInvoke(SystemInterceptorProxy.java:140)
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 com.sun.ejb.containers.interceptors.AroundInvokeInterceptor.intercept(InterceptorManager.java:883)
at com.sun.ejb.containers.interceptors.AroundInvokeChainImpl.invokeNext(InterceptorManager.java:822)
at com.sun.ejb.containers.interceptors.InterceptorManager.intercept(InterceptorManager.java:369)
at com.sun.ejb.containers.BaseContainer.__intercept(BaseContainer.java:4758)
at com.sun.ejb.containers.BaseContainer.intercept(BaseContainer.java:4746)
at com.sun.ejb.containers.EJBLocalObjectInvocationHandler.invoke(EJBLocalObjectInvocationHandler.java:212)
... 34 more
我已经尝试过回应：
我想知道：
- 为什么我会得到这个异常？
- 当我使用“在服务器上运行”选项运行此应用程序时，它打开它无法找到的Url localhost：8080/Guestbook。当我输入localhost：8080/Guestbook/guest.jsp然后页面打开正确，但是当我输入guestname并按下“添加”按钮。我得到以上例外。
我如何让它打开本地主机：//8080留言guest.jsp代替本地主机：8080 /留言？
请注意，我已经做到了准确，已在网站像persistence.xml文件的位置，在.java文件等的代码描述的方式