java - 使用 EJB 3.0 删除数据库行

Question

我想删除数据库中的一行，所以我创建了一个 EJB 来帮我完成这件事

@Stateless(name = "ejbs/AdminAcountEJB")
public class AdminAcountEJB implements IAdminAcountEJB  {

    @PersistenceContext
    private EntityManager entityManager;

    public void deleteRecord(Record record) {
                    entityManager.remove(record);
    }
}

我没有创建 TransactionEntity 对象然后使用 begin() 方法，因为据我所知，EJB 已经是事务安全的。

为了查看它是否在用户界面(一个 JSF 2.0 页面)中工作，我创建了一个数据表，其中有一列带有删除命令链接，并从连接到 EJB 的 backingbean 触发它:

页面

<h:dataTable value="#{managementBB.retrieveRecords()}" var="record">
                   ...
                    <h:column>
    <h:commandLink value="X" action="#{managementBB.deleteRow(record)}"/>
                    </h:column>
</h:dataTable>

支持 bean

 @Named("managementBB")
@SessionScoped
public class ManagementBB implements Serializable{

    @EJB
    private IAdminAcountEJB managementEJB;

    //...

    public String deleteRow(Record record) {

        managementEJB.deleteRecord(record);
        return "manage?faces-redirect=true;";
    }

这是我在点击链接删除行时在控制台中看到的错误:

WARNING: StandardWrapperValve[Faces Servlet]: PWC1406: Servlet.service() for servlet Faces Servlet threw exception javax.faces.el.EvaluationException: javax.ejb.EJBException at javax.faces.component.MethodBindingMethodExpressionAdapter.invoke(MethodBindingMethodExpressionAdapter.java:102) at com.sun.faces.application.ActionListenerImpl.processAction(ActionListenerImpl.java:102) at javax.faces.component.UICommand.broadcast(UICommand.java:315) at javax.faces.component.UIData.broadcast(UIData.java:912) at javax.faces.component.UIViewRoot.broadcastEvents(UIViewRoot.java:775) at javax.faces.component.UIViewRoot.processApplication(UIViewRoot.java:1267) at com.sun.faces.lifecycle.InvokeApplicationPhase.execute(InvokeApplicationPhase.java:82) at com.sun.faces.lifecycle.Phase.doPhase(Phase.java:101) at com.sun.faces.lifecycle.LifecycleImpl.execute(LifecycleImpl.java:118) at javax.faces.webapp.FacesServlet.service(FacesServlet.java:312) at org.apache.catalina.core.StandardWrapper.service(StandardWrapper.java:1523) at org.apache.catalina.core.StandardWrapperValve.invoke(StandardWrapperValve.java:279) at org.apache.catalina.core.StandardContextValve.invoke(StandardContextValve.java:188) at org.apache.catalina.core.StandardPipeline.invoke(StandardPipeline.java:641) at com.sun.enterprise.web.WebPipeline.invoke(WebPipeline.java:97) at com.sun.enterprise.web.PESessionLockingStandardPipeline.invoke(PESessionLockingStandardPipeline.java:85) at org.apache.catalina.core.StandardHostValve.invoke(StandardHostValve.java:185) at org.apache.catalina.connector.CoyoteAdapter.doService(CoyoteAdapter.java:325) at org.apache.catalina.connector.CoyoteAdapter.service(CoyoteAdapter.java:226) at com.sun.enterprise.v3.services.impl.ContainerMapper.service(ContainerMapper.java:165) at com.sun.grizzly.http.ProcessorTask.invokeAdapter(ProcessorTask.java:791) at com.sun.grizzly.http.ProcessorTask.doProcess(ProcessorTask.java:693) at com.sun.grizzly.http.ProcessorTask.process(ProcessorTask.java:954) at com.sun.grizzly.http.DefaultProtocolFilter.execute(DefaultProtocolFilter.java:170) at com.sun.grizzly.DefaultProtocolChain.executeProtocolFilter(DefaultProtocolChain.java:135) at com.sun.grizzly.DefaultProtocolChain.execute(DefaultProtocolChain.java:102) at com.sun.grizzly.DefaultProtocolChain.execute(DefaultProtocolChain.java:88) at com.sun.grizzly.http.HttpProtocolChain.execute(HttpProtocolChain.java:76) at com.sun.grizzly.ProtocolChainContextTask.doCall(ProtocolChainContextTask.java:53) at com.sun.grizzly.SelectionKeyContextTask.call(SelectionKeyContextTask.java:57) at com.sun.grizzly.ContextTask.run(ContextTask.java:69) at com.sun.grizzly.util.AbstractThreadPool$Worker.doWork(AbstractThreadPool.java:330) at com.sun.grizzly.util.AbstractThreadPool$Worker.run(AbstractThreadPool.java:309) at java.lang.Thread.run(Thread.java:662) Caused by: javax.ejb.EJBException at com.sun.ejb.containers.BaseContainer.processSystemException(BaseContainer.java:5119) at com.sun.ejb.containers.BaseContainer.completeNewTx(BaseContainer.java:5017) at com.sun.ejb.containers.BaseContainer.postInvokeTx(BaseContainer.java:4805) at com.sun.ejb.containers.BaseContainer.postInvoke(BaseContainer.java:2004) at com.sun.ejb.containers.BaseContainer.postInvoke(BaseContainer.java:1955) at com.sun.ejb.containers.EJBLocalObjectInvocationHandler.invoke(EJBLocalObjectInvocationHandler.java:198) at com.sun.ejb.containers.EJBLocalObjectInvocationHandlerDelegate.invoke(EJBLocalObjectInvocationHandlerDelegate.java:84) at $Proxy162.deleteRecord(Unknown Source) at backingbeans.ManagementBB.deleteRow(ManagementBB.java:46) at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method) at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:39) at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:25) at java.lang.reflect.Method.invoke(Method.java:597) at org.jboss.weld.util.reflection.SecureReflections$13.work(SecureReflections.java:304) at org.jboss.weld.util.reflection.SecureReflectionAccess.run(SecureReflectionAccess.java:54) at org.jboss.weld.util.reflection.SecureReflectionAccess.runAsInvocation(SecureReflectionAccess.java:163) at org.jboss.weld.util.reflection.SecureReflections.invoke(SecureReflections.java:298) at org.jboss.weld.bean.proxy.ClientProxyMethodHandler.invoke(ClientProxyMethodHandler.java:113) at org.jboss.weld.util.CleanableMethodHandler.invoke(CleanableMethodHandler.java:43) at backingbeans.ManagementBB_$$_javassist_132.deleteRow(ManagementBB_$$_javassist_132.java) at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method) at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:39) at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:25) at java.lang.reflect.Method.invoke(Method.java:597) at javax.el.BeanELResolver.invokeMethod(BeanELResolver.java:737) at javax.el.BeanELResolver.invoke(BeanELResolver.java:467) at javax.el.CompositeELResolver.invoke(CompositeELResolver.java:246) at com.sun.el.parser.AstValue.invoke(AstValue.java:228) at com.sun.el.MethodExpressionImpl.invoke(MethodExpressionImpl.java:297) at org.jboss.weld.util.el.ForwardingMethodExpression.invoke(ForwardingMethodExpression.java:43) at org.jboss.weld.el.WeldMethodExpression.invoke(WeldMethodExpression.java:72) at com.sun.faces.facelets.el.TagMethodExpression.invoke(TagMethodExpression.java:98) at javax.faces.component.MethodBindingMethodExpressionAdapter.invoke(MethodBindingMethodExpressionAdapter.java:88) ... 33 more Caused by: java.lang.IllegalArgumentException: Entity must be managed to call remove: entities.Record@df8b3d, try merging the detached and try the remove again. at org.eclipse.persistence.internal.sessions.UnitOfWorkImpl.performRemove(UnitOfWorkImpl.java:3539) at org.eclipse.persistence.internal.jpa.EntityManagerImpl.remove(EntityManagerImpl.java:435) at com.sun.enterprise.container.common.impl.EntityManagerWrapper.remove(EntityManagerWrapper.java:292) at ejbs.AdminAcountEJB.deleteRecord(AdminAcountEJB.java:23) at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method) at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:39) at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:25) at java.lang.reflect.Method.invoke(Method.java:597) at org.glassfish.ejb.security.application.EJBSecurityManager.runMethod(EJBSecurityManager.java:1056) at org.glassfish.ejb.security.application.EJBSecurityManager.invoke(EJBSecurityManager.java:1128) at com.sun.ejb.containers.BaseContainer.invokeBeanMethod(BaseContainer.java:5292) at com.sun.ejb.EjbInvocation.invokeBeanMethod(EjbInvocation.java:615) at com.sun.ejb.containers.interceptors.AroundInvokeChainImpl.invokeNext(InterceptorManager.java:797) at com.sun.ejb.EjbInvocation.proceed(EjbInvocation.java:567) at org.jboss.weld.ejb.SessionBeanInterceptor.aroundInvoke(SessionBeanInterceptor.java:47) at sun.reflect.GeneratedMethodAccessor87.invoke(Unknown Source) at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:25) at java.lang.reflect.Method.invoke(Method.java:597) at com.sun.ejb.containers.interceptors.AroundInvokeInterceptor.intercept(InterceptorManager.java:858) at com.sun.ejb.containers.interceptors.AroundInvokeChainImpl.invokeNext(InterceptorManager.java:797) at com.sun.ejb.EjbInvocation.proceed(EjbInvocation.java:567) at com.sun.ejb.containers.interceptors.SystemInterceptorProxy.doAround(SystemInterceptorProxy.java:157) at com.sun.ejb.containers.interceptors.SystemInterceptorProxy.aroundInvoke(SystemInterceptorProxy.java:139) at sun.reflect.GeneratedMethodAccessor86.invoke(Unknown Source) at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:25) at java.lang.reflect.Method.invoke(Method.java:597) at com.sun.ejb.containers.interceptors.AroundInvokeInterceptor.intercept(InterceptorManager.java:858) at com.sun.ejb.containers.interceptors.AroundInvokeChainImpl.invokeNext(InterceptorManager.java:797) at com.sun.ejb.containers.interceptors.InterceptorManager.intercept(InterceptorManager.java:367) at com.sun.ejb.containers.BaseContainer.__intercept(BaseContainer.java:5264) at com.sun.ejb.containers.BaseContainer.intercept(BaseContainer.java:5252) at com.sun.ejb.containers.EJBLocalObjectInvocationHandler.invoke(EJBLocalObjectInvocationHandler.java:190) ... 60 more

如您所见，我将 CDI 用于 beans(@Named) 而不是 @ManagedBeans，但我希望这不是原因。另外我想提一下，在我的数据库中，我有一个独立的表，与 Record 表完全无关，这会影响吗？

Answer 1

答案可以在以下几行中的堆栈跟踪中找到:

Caused by: java.lang.IllegalArgumentException: Entity must be managed to call remove: entities.Record@df8b3d, try merging the detached and try the remove again.

EntityManager.remove要求作为参数传入的引用是托管实体，即对象必须存在于持久性上下文中。如果您从 JSF 托管 bean 或 CDI 托管 bean 传递实体引用，它仍然是一个非托管/分离实体，除非您最初是从当前持久性上下文中获取实体引用。

要进一步了解这一点，您应该了解 JPA 实体生命周期。在大多数情况下，您从持久性上下文中获取的托管实体在事务结束时分离(即当持久性上下文结束时)。因此，您的 JSF/CDI 托管 bean 将使用分离的实体而不是托管实体。当您将分离的实体从 JSF 传递回 EJB 时，调用 EntityManager.remove 将导致所描述的 IllegalArgumentException。

因此，解决方案是使用分离实体获取对托管实体的引用，使用 EntityManager.merge (它将分离实体的内容与持久性上下文合并，并返回对托管实体的引用)或 EntityManager.find (它从持久性上下文返回一个托管实体，如果它存在的话)。我更喜欢在可能修改分离实体的情况下使用 EntityManager.find - 当分离实体与其他实体有关系时，MERGE 可能是级联，而 REMOVE 操作可能不会，如果您在定义必须级联的操作时不小心。