我有一个标记为@Startup和@Singleton的类，构造函数被调用两次。
为什么被叫两次？
这是班级：
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，构造函数都是从相同的类加载器中调用的。
构造函数中的堆栈跟踪都引导wlfullclient-12.1.1jar，但堆栈跟踪 则不同。
以下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_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
答案 0 :(得分：10)
第一个堆栈实际上并不是创建 bean 实例，而是创建代理实例。您的@Singleton未声明任何业务接口，因此默认情况下它使用无接口视图（可以使用@LocalBean显式配置）。使用无接口视图时，容器会生成一个代理类，该代理类是类的子类（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动到@PostConstruct。 Java构造函数与无接口视图混合不好。