Question

在我们将应用程序从JBoss 4迁移到JBoss 5之后，当使用 Bean-Managed Transaction （BMT）会话Bean完成延迟加载时，我们得到org.hibernate.LazyInitializationException。

我知道在Web开发方面这是一个众所周知的问题，但是我们没有从Web组件进行延迟加载，我们只是在一次调用中在Bean内部进行。

如果我们将bean更改为CMT一切正常，但生产类很大，并且这样做可能不是一种选择。

为什么会发生这种情况？有什么方法可以解决这个问题？

BMT无状态会话Bean

@Stateless
@TransactionManagement(TransactionManagementType.BEAN)
public class BMTBean implements BMTBeanLocal{

    @PersistenceContext
    private EntityManager em;

    @Override
    public void customerOperation() {

        Customer customer = em.find(Customer.class, 1);     
        List<Address> list = customer.getAddresses();       
        String streetName = list.get(0).getStreet(); // The error happens here!

        System.out.println("Street: " + streetName);
    }
}

客户实体

@Entity
@Table
public class Customer {

    @Id
    @Column
    private Integer id;

    @Column
    private String name;

    @OneToMany(fetch=FetchType.LAZY, mappedBy="customer")   
    private List<Address> addresses;

}

延迟加载的地址实体

@Entity
@Table
public class Address {

    @Id
    @Column
    private Integer id;

    @Column
    private String street;

    @ManyToOne(fetch=FetchType.LAZY)
    @JoinColumn(name="CUSTOMER_ID", insertable = false, updatable = false)
    private Customer customer;

}

详细例外

13:12:45,374 ERROR [LazyInitializationException] failed to lazily initialize a collection of role: entity.Customer.addresses, no session or session was closed
org.hibernate.LazyInitializationException: failed to lazily initialize a collection of role: entity.Customer.addresses, no session or session was closed
    at org.hibernate.collection.AbstractPersistentCollection.throwLazyInitializationException(AbstractPersistentCollection.java:380)
    at org.hibernate.collection.AbstractPersistentCollection.throwLazyInitializationExceptionIfNotConnected(AbstractPersistentCollection.java:372)
    at org.hibernate.collection.AbstractPersistentCollection.initialize(AbstractPersistentCollection.java:365)
    at org.hibernate.collection.AbstractPersistentCollection.read(AbstractPersistentCollection.java:108)
    at org.hibernate.collection.PersistentBag.get(PersistentBag.java:445)
    at bean.BMTBean.customerOperation(BMTBean.java:26)
    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.aop.joinpoint.MethodInvocation.invokeTarget(MethodInvocation.java:122)
    at org.jboss.aop.joinpoint.MethodInvocation.invokeNext(MethodInvocation.java:111)
    at org.jboss.ejb3.EJBContainerInvocationWrapper.invokeNext(EJBContainerInvocationWrapper.java:69)
    at org.jboss.ejb3.interceptors.aop.InterceptorSequencer.invoke(InterceptorSequencer.java:73)
    at org.jboss.ejb3.interceptors.aop.InterceptorSequencer.aroundInvoke(InterceptorSequencer.java:59)
    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.aop.advice.PerJoinpointAdvice.invoke(PerJoinpointAdvice.java:174)
    at org.jboss.aop.joinpoint.MethodInvocation.invokeNext(MethodInvocation.java:102)
    at org.jboss.ejb3.interceptors.aop.InvocationContextInterceptor.fillMethod(InvocationContextInterceptor.java:72)
    at org.jboss.aop.advice.org.jboss.ejb3.interceptors.aop.InvocationContextInterceptor_z_fillMethod_328422269.invoke(InvocationContextInterceptor_z_fillMethod_328422269.java)
    at org.jboss.aop.joinpoint.MethodInvocation.invokeNext(MethodInvocation.java:102)
    at org.jboss.ejb3.interceptors.aop.InvocationContextInterceptor.setup(InvocationContextInterceptor.java:88)
    at org.jboss.aop.advice.org.jboss.ejb3.interceptors.aop.InvocationContextInterceptor_z_setup_328422269.invoke(InvocationContextInterceptor_z_setup_328422269.java)
    at org.jboss.aop.joinpoint.MethodInvocation.invokeNext(MethodInvocation.java:102)
    at org.jboss.ejb3.connectionmanager.CachedConnectionInterceptor.invoke(CachedConnectionInterceptor.java:62)
    at org.jboss.aop.joinpoint.MethodInvocation.invokeNext(MethodInvocation.java:102)
    at org.jboss.ejb3.entity.TransactionScopedEntityManagerInterceptor.invoke(TransactionScopedEntityManagerInterceptor.java:56)
    at org.jboss.aop.joinpoint.MethodInvocation.invokeNext(MethodInvocation.java:102)
    at org.jboss.ejb3.AllowedOperationsInterceptor.invoke(AllowedOperationsInterceptor.java:47)
    at org.jboss.aop.joinpoint.MethodInvocation.invokeNext(MethodInvocation.java:102)
    at org.jboss.ejb3.tx.StatelessBMTInterceptor.handleInvocation(StatelessBMTInterceptor.java:106)
    at org.jboss.ejb3.tx.BMTInterceptor.invoke(BMTInterceptor.java:55)
    at org.jboss.aop.joinpoint.MethodInvocation.invokeNext(MethodInvocation.java:102)
    at org.jboss.ejb3.stateless.StatelessInstanceInterceptor.invoke(StatelessInstanceInterceptor.java:68)
    at org.jboss.aop.joinpoint.MethodInvocation.invokeNext(MethodInvocation.java:102)
    at org.jboss.ejb3.tx.NullInterceptor.invoke(NullInterceptor.java:42)
    at org.jboss.aop.joinpoint.MethodInvocation.invokeNext(MethodInvocation.java:102)
    at org.jboss.aspects.tx.TxPropagationInterceptor.invoke(TxPropagationInterceptor.java:76)
    at org.jboss.aop.joinpoint.MethodInvocation.invokeNext(MethodInvocation.java:102)
    at org.jboss.ejb3.tx.NullInterceptor.invoke(NullInterceptor.java:42)
    at org.jboss.aop.joinpoint.MethodInvocation.invokeNext(MethodInvocation.java:102)
    at org.jboss.ejb3.security.Ejb3AuthenticationInterceptorv2.invoke(Ejb3AuthenticationInterceptorv2.java:186)
    at org.jboss.aop.joinpoint.MethodInvocation.invokeNext(MethodInvocation.java:102)
    at org.jboss.ejb3.ENCPropagationInterceptor.invoke(ENCPropagationInterceptor.java:41)
    at org.jboss.aop.joinpoint.MethodInvocation.invokeNext(MethodInvocation.java:102)
    at org.jboss.ejb3.BlockContainerShutdownInterceptor.invoke(BlockContainerShutdownInterceptor.java:67)
    at org.jboss.aop.joinpoint.MethodInvocation.invokeNext(MethodInvocation.java:102)
    at org.jboss.aspects.currentinvocation.CurrentInvocationInterceptor.invoke(CurrentInvocationInterceptor.java:67)
    at org.jboss.aop.joinpoint.MethodInvocation.invokeNext(MethodInvocation.java:102)
    at org.jboss.ejb3.session.SessionSpecContainer.invoke(SessionSpecContainer.java:176)
    at org.jboss.ejb3.session.SessionSpecContainer.invoke(SessionSpecContainer.java:216)
    at org.jboss.ejb3.proxy.impl.handler.session.SessionProxyInvocationHandlerBase.invoke(SessionProxyInvocationHandlerBase.java:207)
    at org.jboss.ejb3.proxy.impl.handler.session.SessionProxyInvocationHandlerBase.invoke(SessionProxyInvocationHandlerBase.java:164)
    at com.sun.proxy.$Proxy492.customerOperation(Unknown Source)
    at servlets.BMTServlet.doGet(BMTServlet.java:29)
    at javax.servlet.http.HttpServlet.service(HttpServlet.java:617)
    at javax.servlet.http.HttpServlet.service(HttpServlet.java:717)
    at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:290)
    at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:206)
    at org.jboss.web.tomcat.filters.ReplyHeaderFilter.doFilter(ReplyHeaderFilter.java:96)
    at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:235)
    at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:206)
    at org.apache.catalina.core.StandardWrapperValve.invoke(StandardWrapperValve.java:235)
    at org.apache.catalina.core.StandardContextValve.invoke(StandardContextValve.java:191)
    at org.jboss.web.tomcat.security.SecurityAssociationValve.invoke(SecurityAssociationValve.java:190)
    at org.jboss.web.tomcat.security.JaccContextValve.invoke(JaccContextValve.java:92)
    at org.jboss.web.tomcat.security.SecurityContextEstablishmentValve.process(SecurityContextEstablishmentValve.java:126)
    at org.jboss.web.tomcat.security.SecurityContextEstablishmentValve.invoke(SecurityContextEstablishmentValve.java:70)
    at org.apache.catalina.core.StandardHostValve.invoke(StandardHostValve.java:127)
    at org.apache.catalina.valves.ErrorReportValve.invoke(ErrorReportValve.java:102)
    at org.jboss.web.tomcat.service.jca.CachedConnectionValve.invoke(CachedConnectionValve.java:158)
    at org.apache.catalina.core.StandardEngineValve.invoke(StandardEngineValve.java:109)
    at org.apache.catalina.connector.CoyoteAdapter.service(CoyoteAdapter.java:330)
    at org.apache.coyote.http11.Http11Processor.process(Http11Processor.java:829)
    at org.apache.coyote.http11.Http11Protocol$Http11ConnectionHandler.process(Http11Protocol.java:598)
    at org.apache.tomcat.util.net.JIoEndpoint$Worker.run(JIoEndpoint.java:447)
    at java.lang.Thread.run(Thread.java:662)
13:12:45,376 ERROR [[BMTServlet]] Servlet.service() for servlet BMTServlet threw exception
org.hibernate.LazyInitializationException: failed to lazily initialize a collection of role: entity.Customer.addresses, no session or session was closed
    at org.hibernate.collection.AbstractPersistentCollection.throwLazyInitializationException(AbstractPersistentCollection.java:380)
    at org.hibernate.collection.AbstractPersistentCollection.throwLazyInitializationExceptionIfNotConnected(AbstractPersistentCollection.java:372)
    at org.hibernate.collection.AbstractPersistentCollection.initialize(AbstractPersistentCollection.java:365)
    at org.hibernate.collection.AbstractPersistentCollection.read(AbstractPersistentCollection.java:108)
    at org.hibernate.collection.PersistentBag.get(PersistentBag.java:445)
    at bean.BMTBean.customerOperation(BMTBean.java:26)
    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.aop.joinpoint.MethodInvocation.invokeTarget(MethodInvocation.java:122)
    at org.jboss.aop.joinpoint.MethodInvocation.invokeNext(MethodInvocation.java:111)
    at org.jboss.ejb3.EJBContainerInvocationWrapper.invokeNext(EJBContainerInvocationWrapper.java:69)
    at org.jboss.ejb3.interceptors.aop.InterceptorSequencer.invoke(InterceptorSequencer.java:73)
    at org.jboss.ejb3.interceptors.aop.InterceptorSequencer.aroundInvoke(InterceptorSequencer.java:59)
    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.aop.advice.PerJoinpointAdvice.invoke(PerJoinpointAdvice.java:174)
    at org.jboss.aop.joinpoint.MethodInvocation.invokeNext(MethodInvocation.java:102)
    at org.jboss.ejb3.interceptors.aop.InvocationContextInterceptor.fillMethod(InvocationContextInterceptor.java:72)
    at org.jboss.aop.advice.org.jboss.ejb3.interceptors.aop.InvocationContextInterceptor_z_fillMethod_328422269.invoke(InvocationContextInterceptor_z_fillMethod_328422269.java)
    at org.jboss.aop.joinpoint.MethodInvocation.invokeNext(MethodInvocation.java:102)
    at org.jboss.ejb3.interceptors.aop.InvocationContextInterceptor.setup(InvocationContextInterceptor.java:88)
    at org.jboss.aop.advice.org.jboss.ejb3.interceptors.aop.InvocationContextInterceptor_z_setup_328422269.invoke(InvocationContextInterceptor_z_setup_328422269.java)
    at org.jboss.aop.joinpoint.MethodInvocation.invokeNext(MethodInvocation.java:102)
    at org.jboss.ejb3.connectionmanager.CachedConnectionInterceptor.invoke(CachedConnectionInterceptor.java:62)
    at org.jboss.aop.joinpoint.MethodInvocation.invokeNext(MethodInvocation.java:102)
    at org.jboss.ejb3.entity.TransactionScopedEntityManagerInterceptor.invoke(TransactionScopedEntityManagerInterceptor.java:56)
    at org.jboss.aop.joinpoint.MethodInvocation.invokeNext(MethodInvocation.java:102)
    at org.jboss.ejb3.AllowedOperationsInterceptor.invoke(AllowedOperationsInterceptor.java:47)
    at org.jboss.aop.joinpoint.MethodInvocation.invokeNext(MethodInvocation.java:102)
    at org.jboss.ejb3.tx.StatelessBMTInterceptor.handleInvocation(StatelessBMTInterceptor.java:106)
    at org.jboss.ejb3.tx.BMTInterceptor.invoke(BMTInterceptor.java:55)
    at org.jboss.aop.joinpoint.MethodInvocation.invokeNext(MethodInvocation.java:102)
    at org.jboss.ejb3.stateless.StatelessInstanceInterceptor.invoke(StatelessInstanceInterceptor.java:68)
    at org.jboss.aop.joinpoint.MethodInvocation.invokeNext(MethodInvocation.java:102)
    at org.jboss.ejb3.tx.NullInterceptor.invoke(NullInterceptor.java:42)
    at org.jboss.aop.joinpoint.MethodInvocation.invokeNext(MethodInvocation.java:102)
    at org.jboss.aspects.tx.TxPropagationInterceptor.invoke(TxPropagationInterceptor.java:76)
    at org.jboss.aop.joinpoint.MethodInvocation.invokeNext(MethodInvocation.java:102)
    at org.jboss.ejb3.tx.NullInterceptor.invoke(NullInterceptor.java:42)
    at org.jboss.aop.joinpoint.MethodInvocation.invokeNext(MethodInvocation.java:102)
    at org.jboss.ejb3.security.Ejb3AuthenticationInterceptorv2.invoke(Ejb3AuthenticationInterceptorv2.java:186)
    at org.jboss.aop.joinpoint.MethodInvocation.invokeNext(MethodInvocation.java:102)
    at org.jboss.ejb3.ENCPropagationInterceptor.invoke(ENCPropagationInterceptor.java:41)
    at org.jboss.aop.joinpoint.MethodInvocation.invokeNext(MethodInvocation.java:102)
    at org.jboss.ejb3.BlockContainerShutdownInterceptor.invoke(BlockContainerShutdownInterceptor.java:67)
    at org.jboss.aop.joinpoint.MethodInvocation.invokeNext(MethodInvocation.java:102)
    at org.jboss.aspects.currentinvocation.CurrentInvocationInterceptor.invoke(CurrentInvocationInterceptor.java:67)
    at org.jboss.aop.joinpoint.MethodInvocation.invokeNext(MethodInvocation.java:102)
    at org.jboss.ejb3.session.SessionSpecContainer.invoke(SessionSpecContainer.java:176)
    at org.jboss.ejb3.session.SessionSpecContainer.invoke(SessionSpecContainer.java:216)
    at org.jboss.ejb3.proxy.impl.handler.session.SessionProxyInvocationHandlerBase.invoke(SessionProxyInvocationHandlerBase.java:207)
    at org.jboss.ejb3.proxy.impl.handler.session.SessionProxyInvocationHandlerBase.invoke(SessionProxyInvocationHandlerBase.java:164)
    at com.sun.proxy.$Proxy492.customerOperation(Unknown Source)
    at servlets.BMTServlet.doGet(BMTServlet.java:29)
    at javax.servlet.http.HttpServlet.service(HttpServlet.java:617)
    at javax.servlet.http.HttpServlet.service(HttpServlet.java:717)
    at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:290)
    at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:206)
    at org.jboss.web.tomcat.filters.ReplyHeaderFilter.doFilter(ReplyHeaderFilter.java:96)
    at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:235)
    at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:206)
    at org.apache.catalina.core.StandardWrapperValve.invoke(StandardWrapperValve.java:235)
    at org.apache.catalina.core.StandardContextValve.invoke(StandardContextValve.java:191)
    at org.jboss.web.tomcat.security.SecurityAssociationValve.invoke(SecurityAssociationValve.java:190)
    at org.jboss.web.tomcat.security.JaccContextValve.invoke(JaccContextValve.java:92)
    at org.jboss.web.tomcat.security.SecurityContextEstablishmentValve.process(SecurityContextEstablishmentValve.java:126)
    at org.jboss.web.tomcat.security.SecurityContextEstablishmentValve.invoke(SecurityContextEstablishmentValve.java:70)
    at org.apache.catalina.core.StandardHostValve.invoke(StandardHostValve.java:127)
    at org.apache.catalina.valves.ErrorReportValve.invoke(ErrorReportValve.java:102)
    at org.jboss.web.tomcat.service.jca.CachedConnectionValve.invoke(CachedConnectionValve.java:158)
    at org.apache.catalina.core.StandardEngineValve.invoke(StandardEngineValve.java:109)
    at org.apache.catalina.connector.CoyoteAdapter.service(CoyoteAdapter.java:330)
    at org.apache.coyote.http11.Http11Processor.process(Http11Processor.java:829)
    at org.apache.coyote.http11.Http11Protocol$Http11ConnectionHandler.process(Http11Protocol.java:598)
    at org.apache.tomcat.util.net.JIoEndpoint$Worker.run(JIoEndpoint.java:447)
    at java.lang.Thread.run(Thread.java:662)

Answer 1

当您没有加载该类的关系并尝试访问它时，会发生LazyInitializationException。

想象一下这个课程：

@Entity
public class Person {
    @OneToOne
    private Dog dog;

    @OneToMany
    private List<Email> emailList;
}

从数据库加载Person时会发生两件事：

狗将默认加载
默认情况下不会加载emailList

您收到的错误是因为未加载地址。 JPA规则是：

默认情况下，每个以“* One”结束的关系都会被加载，它被定义为EAGER
默认情况下，每个以“* Many”结尾的关系都会 NOT 加载，定义为LAZY

什么是懒惰？ Lazy意味着只有在访问属性后才会加载关系。当你执行person.getEmailList（）时，JPA将查找连接以从数据库中获取EmailList。

问题是：如果连接关闭会发生什么？您将收到错误LazyInitializationException。

如何解决？你有一些选择：

您可以创建一个查询：从Person p left join fetch p.emailList e中选择p。像这样，JPA将加载电子邮件列表
您可以更改关系注释：@OneToMany(fetch = FetchType.EAGER)。使用此配置，JPA将始终加载关系。这种方法的问题在于您将始终加载它。如果您有一个很长的列表，但只想访问可能会降低项目性能的person.name（）。
保持连接打开：就像：

//打开连接 //得到实体 //访问列表 //关闭连接

这种方法的问题在于，如果您忘记关闭连接，您将会泄漏资源。此方法的其他问题是您将获得N + 1效果。 N + 1表示系统能够对数据库执行多个请求。
使用OpenSessionInView模式。与选项3类似，但您将拥有请求的全局处理程序。您将拥有一个可以处理连接的过滤器。

如果您想了解有关此错误的N + 1的更多信息，请查看以下链接：http://uaihebert.com/four-solutions-to-the-lazyinitializationexception/

Bean-Managed Transaction和org.hibernate.LazyInitializationException

1 个答案: