java - @Startup @Singleton 在 WebLogic (EJB 3.1) 中实例化了两次

Question

我有一个标记为 @Startup 和 @Singleton 的类，构造函数被调用了两次。

为什么会被调用两次？

• 网络逻辑 12.1.1
• 本地运行(非集群)
• @PostConstruct 在那里时也被调用了两次
• 与 XML 配置无关(weblogic-ejb-jar.xml 等)

这是类:

import java.util.concurrent.atomic.AtomicInteger;

import javax.ejb.Singleton;
import javax.ejb.Startup;

@Startup
@Singleton
public class CacheStartupListener {

    static AtomicInteger count= new AtomicInteger(0); 

    public CacheStartupListener() {
        System.err.println("Singleton invoked " + count.incrementAndGet() + " " + getClass().getClassLoader().toString());  
    }
}

我可以从输出中看到，两次都是从相同 类加载器调用构造函数。

构造函数中的堆栈跟踪均通过 wlfullclient-12.1.1jar，但堆栈跟踪在其他方面有所不同。

这是第一个实例化的堆栈跟踪:

Daemon Thread [[ACTIVE] ExecuteThread: '0' for queue: 'weblogic.kernel.Default (self-tuning)'] (Suspended (breakpoint at line 30 in CacheStartupListener)) (out of synch)   
    CacheStartupListener_m3hhum_NoIntfViewImpl(CacheStartupListener).<init>() line: 30 (out of synch)   
    CacheStartupListener_m3hhum_NoIntfViewImpl.<init>(SingletonLocalObject) line: not available 
    NativeConstructorAccessorImpl.newInstance0(Constructor, Object[]) line: not available [native method]   
    NativeConstructorAccessorImpl.newInstance(Object[]) line: 57    
    DelegatingConstructorAccessorImpl.newInstance(Object[]) line: 45    
    Constructor<T>.newInstance(Object...) line: 525 
    SingletonEJBLocalHomeImpl.allocateBI(Class<T>) line: 45 
    SingletonEJBLocalHomeImpl.prepare() line: 30    
    SingletonSessionBeanInfoImpl(SessionBeanInfoImpl).prepare() line: 458   
    SingletonSessionBeanInfoImpl.prepare() line: 115    
    EJBDeployer.setupBeanInfos() line: 767  
    EJBDeployer.prepare(VirtualJarFile, EjbDescriptorBean) line: 920    
    EJBModule.prepare() line: 419   
    ScopedModuleDriver.prepare() line: 188  
    ExtensibleModuleWrapper.prepare() line: 83  
    ModuleListenerInvoker.prepare() line: 100   
    ModuleStateDriver$1.next(Module) line: 172  
    ModuleStateDriver$1.next(Object) line: 167  
    StateMachineDriver<StateMachine>.nextState(StateChange<StateMachine>, StateMachine[]) line: 35  
    ModuleStateDriver.prepare(Module[]) line: 38    
    DeploymentCallbackFlow.prepare(Module[]) line: 139  
    DeploymentCallbackFlow.prepare() line: 55   
    BaseDeployment$1.next(Object) line: 706 
    StateMachineDriver<StateMachine>.nextState(StateChange<StateMachine>, StateMachine[]) line: 35  
    EarDeployment(BaseDeployment).prepare(DeploymentContext) line: 237  
    EarDeployment.prepare(DeploymentContext) line: 61   
    DeploymentStateChecker.prepare(DeploymentContext) line: 158 
    AppContainerInvoker.prepare(DeploymentContext) line: 60 
    RedeployOperation.createAndPrepareContainer() line: 104 
    RedeployOperation.doPrepare() line: 138 
    RedeployOperation(AbstractOperation).prepare() line: 229    
    DeploymentManager.handleDeploymentPrepare(Deployment, DeploymentManager$DeploymentRequestInfo) line: 747    
    DeploymentManager.prepareDeploymentList(ArrayList, DeploymentContext) line: 1216    
    DeploymentManager.handlePrepare(DeploymentContext) line: 250    
    DeploymentServiceDispatcher.prepare(DeploymentContext) line: 159    
    DeploymentReceiverCallbackDeliverer.doPrepareCallback(DeploymentContext) line: 171  
    DeploymentReceiverCallbackDeliverer.access$000(DeploymentReceiverCallbackDeliverer, DeploymentContext) line: 13 
    DeploymentReceiverCallbackDeliverer$1.run() line: 46    
    SelfTuningWorkManagerImpl$WorkAdapterImpl.run() line: 545   
    ExecuteThread.execute(Runnable) line: 256   
    ExecuteThread.run() line: 221   

这是第二次实例化的堆栈跟踪:

Daemon Thread [[ACTIVE] ExecuteThread: '0' for queue: 'weblogic.kernel.Default (self-tuning)'] (Suspended (breakpoint at line 30 in CacheStartupListener)) (out of synch)   
    CacheStartupListener_m3hhum_Impl(CacheStartupListener).<init>() line: 30 (out of synch) 
    CacheStartupListener_m3hhum_Impl.<init>() line: not available   
    NativeConstructorAccessorImpl.newInstance0(Constructor, Object[]) line: not available [native method]   
    NativeConstructorAccessorImpl.newInstance(Object[]) line: 57    
    DelegatingConstructorAccessorImpl.newInstance(Object[]) line: 45    
    Constructor<T>.newInstance(Object...) line: 525 
    WeldConstructorImpl<T>.newInstance(Object...) line: 204 
    ConstructorInjectionPoint<T>.newInstance(BeanManagerImpl, CreationalContext<?>) line: 117   
    ExtendedSessionBean(SessionBean<T>).createInstance(CreationalContext<T>) line: 212  
    ExtendedSessionBean.derivedCreateInstance(CreationalContext) line: 35   
    WeldEjbBeanManager$ExtendedInjectionTarget.produce(CreationalContext) line: 131 
    WeldEjbBeanManager.newBeanInstance(String) line: 78 
    InjectionBasedEjbComponentCreator.getBean(String, Class, boolean) line: 75  
    SingletonSessionManager(BaseEJBManager).createNewBeanInstance() line: 209   
    SingletonSessionManager.constructAndInitBean() line: 353    
    SingletonSessionManager.access$300(SingletonSessionManager) line: 63    
    SingletonSessionManager$SingletonLifecycleManager.doActualInit() line: 798  
    SingletonSessionManager$SingletonLifecycleManager.initInternal(boolean) line: 744   
    SingletonSessionManager$SingletonLifecycleManager.init() line: 631  
    SingletonSessionManager.init() line: 280    
    SingletonSessionManager.perhapsInit() line: 276 
    EJBDeployer.initializeBeans() line: 1287    
    EJBDeployer.start() line: 1174  
    EJBModule.start() line: 590 
    ModuleStateDriver$3.next(Module) line: 213  
    ModuleStateDriver$3.next(Object) line: 208  
    StateMachineDriver<StateMachine>.nextState(StateChange<StateMachine>, StateMachine[]) line: 35  
    ModuleStateDriver.start(Module[]) line: 70  
    ScopedModuleDriver.start() line: 212    
    ExtensibleModuleWrapper.start() line: 111   
    ModuleListenerInvoker.start() line: 124 
    ModuleStateDriver$3.next(Module) line: 213  
    ModuleStateDriver$3.next(Object) line: 208  
    StateMachineDriver<StateMachine>.nextState(StateChange<StateMachine>, StateMachine[]) line: 35  
    ModuleStateDriver.start(Module[]) line: 70  
    StartModulesFlow.activate() line: 24    
    BaseDeployment$2.next(Object) line: 729 
    StateMachineDriver<StateMachine>.nextState(StateChange<StateMachine>, StateMachine[]) line: 35  
    EarDeployment(BaseDeployment).activate(DeploymentContext) line: 258 
    EarDeployment.activate(DeploymentContext) line: 61  
    DeploymentStateChecker.activate(DeploymentContext) line: 165    
    AppContainerInvoker.activate(DeploymentContext) line: 79    
    RedeployOperation(AbstractOperation).activate(Deployment) line: 582 
    RedeployOperation(ActivateOperation).activateDeployment() line: 148 
    RedeployOperation(ActivateOperation).doCommit() line: 114   
    RedeployOperation(AbstractOperation).commit() line: 335 
    DeploymentManager.handleDeploymentCommit(Deployment, AbstractOperation) line: 844   
    DeploymentManager.activateDeploymentList(ArrayList, DeploymentManager$DeploymentRequestInfo) line: 1253 
    DeploymentManager.handleCommit(DeploymentContext) line: 440 
    DeploymentServiceDispatcher.commit(DeploymentContext) line: 163 
    DeploymentReceiverCallbackDeliverer.doCommitCallback(DeploymentContext) line: 195   
    DeploymentReceiverCallbackDeliverer.access$100(DeploymentReceiverCallbackDeliverer, DeploymentContext) line: 13 
    DeploymentReceiverCallbackDeliverer$2.run() line: 68    
    SelfTuningWorkManagerImpl$WorkAdapterImpl.run() line: 545   
    ExecuteThread.execute(Runnable) line: 256   
    ExecuteThread.run() line: 221   

Answer 1

第一个堆栈实际上并不是在创建一个bean 实例，而是一个代理 实例。您的 @Singleton 没有声明任何业务接口(interface)，因此默认情况下它使用无接口(interface) View (可以使用 @LocalBean 显式配置)。使用无界面 View 时，容器会生成一个代理类，它是您的类的子类(在本例中，代理名为 CacheStartupListener_m3hhum_NoIntfViewImpl)。当容器创建此代理子类的实例时，将调用 EJB 类的构造函数。您可以尝试在构造函数中打印 getClass() 来证明这一点。

我强烈建议完全删除 Java 构造函数并将所有初始化逻辑移至 @PostConstruct。 Java 构造函数不能很好地与无界面 View 混合。