java - 无状态 session Bean 可以保护 final方法吗？

Question

我已经定义了一个 session bean 基类。这个类是抽象的并且包含 protected final方法。 session 实现类扩展了抽象类并定义了额外的方法。在部署期间，Glassfish 3.1.2 服务器生成一个异常，说明该方法已被覆盖。

abstract class AbstractSessionBean {
    @PersistenceContext(unitName="primary")
    private EntityManager em;

    protected final EntityManager getEntityManager() {
       return em;
    }
}

@Startup
@Stateless
class RegistrationSessionBean extends AbstractSessionBean {
     public void loadRegistration() {
        ...
     }
}

在部署期间，glassfish 服务器抛出异常。如果我将 AbstractSessionBean 的方法设为非 final方法，则部署成功。

这是否意味着 session bean 不能有 final方法？或者此行为仅特定于 Glassfish 3.1.2。

异常信息是:

[#|2013-08-26T17:45:48.542+0530|SEVERE|glassfish3.1.2|javax.enterprise.system.tools.admin.org.glassfish.deployment.admin|_ThreadID=47;_ThreadName=Thread-2;|Exception while loading the app : EJB Container initialization error
java.lang.RuntimeException: Could not invoke defineClass!
    at com.sun.ejb.containers.EjbOptionalIntfGenerator.makeClass(EjbOptionalIntfGenerator.java:448)
    at com.sun.ejb.containers.EjbOptionalIntfGenerator.access$200(EjbOptionalIntfGenerator.java:64)
    at com.sun.ejb.containers.EjbOptionalIntfGenerator$1.run(EjbOptionalIntfGenerator.java:99)
    at java.security.AccessController.doPrivileged(Native Method)
    at com.sun.ejb.containers.EjbOptionalIntfGenerator.loadClass(EjbOptionalIntfGenerator.java:96)
    at com.sun.ejb.containers.BaseContainer.instantiateOptionalEJBLocalBusinessObjectImpl(BaseContainer.java:3886)
    at com.sun.ejb.containers.StatelessSessionContainer.initializeHome(StatelessSessionContainer.java:253)
    at com.sun.ejb.containers.ContainerFactoryImpl.createContainer(ContainerFactoryImpl.java:167)
    at org.glassfish.ejb.startup.EjbApplication.loadContainers(EjbApplication.java:230)
    at org.glassfish.ejb.startup.EjbDeployer.load(EjbDeployer.java:305)
    at org.glassfish.ejb.startup.EjbDeployer.load(EjbDeployer.java:108)
    at org.glassfish.internal.data.ModuleInfo.load(ModuleInfo.java:186)
    at org.glassfish.internal.data.ApplicationInfo.load(ApplicationInfo.java:264)
    at com.sun.enterprise.v3.server.ApplicationLifecycle.deploy(ApplicationLifecycle.java:460)
    at com.sun.enterprise.v3.server.ApplicationLifecycle.deploy(ApplicationLifecycle.java:240)
    at org.glassfish.deployment.admin.DeployCommand.execute(DeployCommand.java:389)
    at com.sun.enterprise.v3.admin.CommandRunnerImpl$1.execute(CommandRunnerImpl.java:348)
    at com.sun.enterprise.v3.admin.CommandRunnerImpl.doCommand(CommandRunnerImpl.java:363)
    at com.sun.enterprise.v3.admin.CommandRunnerImpl.doCommand(CommandRunnerImpl.java:1085)
    at com.sun.enterprise.v3.admin.CommandRunnerImpl.access$1200(CommandRunnerImpl.java:95)
    at com.sun.enterprise.v3.admin.CommandRunnerImpl$ExecutionContext.execute(CommandRunnerImpl.java:1291)
    at com.sun.enterprise.v3.admin.CommandRunnerImpl$ExecutionContext.execute(CommandRunnerImpl.java:1259)
    at com.sun.enterprise.v3.admin.AdminAdapter.doCommand(AdminAdapter.java:461)
    at com.sun.enterprise.v3.admin.AdminAdapter.service(AdminAdapter.java:212)
    at com.sun.grizzly.tcp.http11.GrizzlyAdapter.service(GrizzlyAdapter.java:179)
    at com.sun.enterprise.v3.server.HK2Dispatcher.dispath(HK2Dispatcher.java:117)
    at com.sun.enterprise.v3.services.impl.ContainerMapper$Hk2DispatcherCallable.call(ContainerMapper.java:354)
    at com.sun.enterprise.v3.services.impl.ContainerMapper.service(ContainerMapper.java:195)
    at com.sun.grizzly.http.ProcessorTask.invokeAdapter(ProcessorTask.java:860)
    at com.sun.grizzly.http.ProcessorTask.doProcess(ProcessorTask.java:757)
    at com.sun.grizzly.http.ProcessorTask.process(ProcessorTask.java:1056)
    at com.sun.grizzly.http.DefaultProtocolFilter.execute(DefaultProtocolFilter.java:229)
    at com.sun.grizzly.DefaultProtocolChain.executeProtocolFilter(DefaultProtocolChain.java:137)
    at com.sun.grizzly.DefaultProtocolChain.execute(DefaultProtocolChain.java:104)
    at com.sun.grizzly.DefaultProtocolChain.execute(DefaultProtocolChain.java:90)
    at com.sun.grizzly.http.HttpProtocolChain.execute(HttpProtocolChain.java:79)
    at com.sun.grizzly.ProtocolChainContextTask.doCall(ProtocolChainContextTask.java:54)
    at com.sun.grizzly.SelectionKeyContextTask.call(SelectionKeyContextTask.java:59)
    at com.sun.grizzly.ContextTask.run(ContextTask.java:71)
    at com.sun.grizzly.util.AbstractThreadPool$Worker.doWork(AbstractThreadPool.java:532)
    at com.sun.grizzly.util.AbstractThreadPool$Worker.run(AbstractThreadPool.java:513)
    at java.lang.Thread.run(Thread.java:724)
Caused by: java.lang.reflect.InvocationTargetException
    at sun.reflect.GeneratedMethodAccessor50.invoke(Unknown Source)
    at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
    at java.lang.reflect.Method.invoke(Method.java:606)
    at com.sun.ejb.containers.EjbOptionalIntfGenerator.makeClass(EjbOptionalIntfGenerator.java:445)
    ... 41 more
Caused by: java.lang.VerifyError: class org.bean.test.persistence.util.__EJB31_Generated__RegistrationSessionBean__Intf____Bean__ overrides final method getContext.()Ljavax/ejb/SessionContext;
    at java.lang.ClassLoader.defineClass1(Native Method)
    at java.lang.ClassLoader.defineClass(ClassLoader.java:792)
    ... 45 more
|#]

Answer 1

简短的回答是"is"，但长的回答是“一般情况下是，但在使用无界面 View 时不是”。对无接口(interface) View 的限制间接来自 EJB 3.2 规范的第 3.4.4 节:

Only public methods of the bean class and of any superclasses except java.lang.Object may be invoked through the no-interface view. Attempted invocations of methods with any other access modifiers via the no-interface view reference must result in the javax.ejb.EJBException.

当生成无接口(interface) View 代理时，EJB 容器必须创建 EJB 类的子类并覆盖所有公共(public)方法以提供代理行为。但是，上面引用的规范中的第二句暗示所有剩余的非私有(private)方法也必须被覆盖，以便抛出无条件的 EJBException。也就是说，来自应用程序服务器的错误消息可能会更好。