LazyInitializationException in JPA and Hibernate

Question

I know that this question has been ask numerous times here and across the internet and I have read through many of those answers but I still don't understand the proper way to solve this problem. I am experimenting with Spring MVC and JPA and every time I access a lazily loaded property I get a LazyInitializationException.

Here is some of the code I am experimenting with:

@Repository
public class MyDAO {
    private static final Logger logger = LoggerFactory.getLogger(MyDAO.class);

    @PersistenceContext
    private EntityManager em;

    @Transactional
    public void logDOI() {
        DOI myDOI = em.find(DOI.class, Long.valueOf(1));

        // This line gives the expected output
        logger.info("Fetched DOI: " + myDOI.getDoiKey());

        // This line throws the LazyInitalizationException
        for(DOIMembership m : myDOI.getDoiMemberships()) {
            logger.info("Got DOI Membership id: " + m.getId());
        }
    }
}

The entity I am accessing:

@Entity
@Table(name="DOI")
public class DOI implements Serializable {
    private static final long serialVersionUID = 1L;

    @Id
    @SequenceGenerator(name="DOI_ID_GENERATOR", sequenceName="DOI_SEQ")
    @GeneratedValue(strategy=GenerationType.SEQUENCE, generator="DOI_ID_GENERATOR")
    private long id;

    // Other properties omitted

    //bi-directional many-to-one association to DOIMembership
    @OneToMany(mappedBy="doi", fetch=FetchType.LAZY)
    private Set<DOIMembership> doiMemberships;

    public DOI() {
    }

    public long getId() {
        return this.id;
    }

    public void setId(long id) {
        this.id = id;
    }

    // Other Accessors Omitted

}

The entity referenced from DOI

@Entity
@Table(name="DOI_MEMBERSHIP")
public class DOIMembership implements Serializable {
    private static final long serialVersionUID = 1L;

    @Id
    @SequenceGenerator(name="DOI_MEMBERSHIP_ID_GENERATOR", sequenceName="DOI_MEMBERSHIP_SEQ")
    @GeneratedValue(strategy=GenerationType.SEQUENCE, generator="DOI_MEMBERSHIP_ID_GENERATOR")
    private long id;

    //bi-directional many-to-one association to DOI
    @ManyToOne(fetch=FetchType.LAZY)
    @JoinColumn(name="DOI_ID")
    private DOI doi;

    @Column(name="GROUP_ID")
    private BigDecimal groupId;

    @Column(name="DATA_SET")
    private BigDecimal dataSetId;

    public DOIMembership() {
    }

    public BigDecimal getGroupId() {
        return groupId;
    }

    public BigDecimal getDataSetId() {
        return dataSetId;
    }

    public void setDataSetId(BigDecimal dataSetId) {
        this.dataSetId = dataSetId;
    }

    public void setGroupId(BigDecimal groupId) {
        this.groupId = groupId;
    }

    public long getId() {
        return this.id;
    }

    public void setId(long id) {
        this.id = id;
    }

    public DOI getDoi() {
        return this.doi;
    }

    public void setDoi(DOI doi) {
        this.doi = doi;
    }

}

The Spring MVC Controller:

@Controller
@RequestMapping("/summary")
public class DOISummaryController {
    @Autowired
    MyDAO myDAO;

    @RequestMapping()
    public String DOISummary() {
        myDAO.logDOI();

        return "home";
    }
}

My Spring configuration:

<?xml version="1.0" encoding="UTF-8"?>
<beans xmlns="http://www.springframework.org/schema/beans"
    xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
    xmlns:context="http://www.springframework.org/schema/context"
    xmlns:task="http://www.springframework.org/schema/task"
    xmlns:tx="http://www.springframework.org/schema/tx"
    xsi:schemaLocation="http://www.springframework.org/schema/tx
        http://www.springframework.org/schema/tx/spring-tx-3.1.xsd
        http://www.springframework.org/schema/beans
        http://www.springframework.org/schema/beans/spring-beans-3.1.xsd
        http://www.springframework.org/schema/task
        http://www.springframework.org/schema/task/spring-task-3.0.xsd
        http://www.springframework.org/schema/context
        http://www.springframework.org/schema/context/spring-context-3.1.xsd">

    <!-- Root Context: defines shared resources visible to all other web components -->

    <context:property-placeholder location="WEB-INF/spring/root-context.properties, WEB-INF/spring/datasource-context.properties"  />

    <bean id="dataSource" class="org.apache.commons.dbcp.BasicDataSource" destroy-method="close">
        <property name="driverClassName">
            <value>oracle.jdbc.driver.OracleDriver</value>
        </property>
        <property name="url">
            <value>${Url}</value>
        </property>
        <property name="username">
            <value>${Username}</value>
        </property>
        <property name="password">
            <value>${Password}</value>
        </property>
    </bean>

    <bean id="emf" class="org.springframework.orm.jpa.LocalContainerEntityManagerFactoryBean">
        <property name="dataSource" ref="dataSource" />
        <property name="jpaVendorAdapter">
            <bean class="org.springframework.orm.jpa.vendor.HibernateJpaVendorAdapter" />
        </property>
        <property name="packagesToScan" value="org.myorg.doi.domain" />
        <property name="jpaProperties">
            <props>
                <prop key="hibernate.dialect">
                    org.hibernate.dialect.Oracle10gDialect
                </prop>
                <prop key="hibernate.max_fetch_depth">3</prop>
                <prop key="hibernate.jdbc.fetch_size">50</prop>
                <prop key="hibernate.jdbc.batch_size">10</prop>
                <prop key="hibernate.show_sql">true</prop>
            </props>
        </property>
    </bean>

    <bean id="transactionManager" class="org.springframework.orm.jpa.JpaTransactionManager">
        <property name="entityManagerFactory" ref="emf" />
    </bean>

    <tx:annotation-driven transaction-manager="transactionManager" />

    <context:annotation-config />

    <task:annotation-driven />

    <context:component-scan base-package="org.myorg.doi" />

</beans>

And a stack trace, as requested:

SEVERE: Servlet.service() for servlet [appServlet] in context with path [/DOI] threw exception [Request processing failed; nested exception is org.hibernate.LazyInitializationException: could not initialize proxy - no Session] with root cause
org.hibernate.LazyInitializationException: could not initialize proxy - no Session
    at org.hibernate.collection.internal.AbstractPersistentCollection.initialize(AbstractPersistentCollection.java:430)
    at org.hibernate.collection.internal.AbstractPersistentCollection.read(AbstractPersistentCollection.java:121)
    at org.hibernate.collection.internal.PersistentSet.iterator(PersistentSet.java:180)
    at org.myorg.doi.dao.MyDAO.logDOI(MyDAO.java:27)
    at org.myorg.doi.web.DOISummaryController.DOISummary(DOISummaryController.java:29)
    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.springframework.web.method.support.InvocableHandlerMethod.invoke(InvocableHandlerMethod.java:213)
    at org.springframework.web.method.support.InvocableHandlerMethod.invokeForRequest(InvocableHandlerMethod.java:126)
    at org.springframework.web.servlet.mvc.method.annotation.ServletInvocableHandlerMethod.invokeAndHandle(ServletInvocableHandlerMethod.java:96)
    at org.springframework.web.servlet.mvc.method.annotation.RequestMappingHandlerAdapter.invokeHandlerMethod(RequestMappingHandlerAdapter.java:617)
    at org.springframework.web.servlet.mvc.method.annotation.RequestMappingHandlerAdapter.handleInternal(RequestMappingHandlerAdapter.java:578)
    at org.springframework.web.servlet.mvc.method.AbstractHandlerMethodAdapter.handle(AbstractHandlerMethodAdapter.java:80)
    at org.springframework.web.servlet.DispatcherServlet.doDispatch(DispatcherServlet.java:923)
    at org.springframework.web.servlet.DispatcherServlet.doService(DispatcherServlet.java:852)
    at org.springframework.web.servlet.FrameworkServlet.processRequest(FrameworkServlet.java:882)
    at org.springframework.web.servlet.FrameworkServlet.doGet(FrameworkServlet.java:778)
    at javax.servlet.http.HttpServlet.service(HttpServlet.java:621)
    at javax.servlet.http.HttpServlet.service(HttpServlet.java:722)
    at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:305)
    at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:210)
    at org.apache.catalina.core.StandardWrapperValve.invoke(StandardWrapperValve.java:225)
    at org.apache.catalina.core.StandardContextValve.invoke(StandardContextValve.java:123)
    at org.apache.catalina.authenticator.AuthenticatorBase.invoke(AuthenticatorBase.java:472)
    at org.apache.catalina.core.StandardHostValve.invoke(StandardHostValve.java:168)
    at org.apache.catalina.valves.ErrorReportValve.invoke(ErrorReportValve.java:98)
    at org.apache.catalina.valves.AccessLogValve.invoke(AccessLogValve.java:927)
    at org.apache.catalina.core.StandardEngineValve.invoke(StandardEngineValve.java:118)
    at com.springsource.insight.collection.tcserver.request.HttpRequestOperationCollectionValve.traceNextValve(HttpRequestOperationCollectionValve.java:116)
    at com.springsource.insight.collection.tcserver.request.HttpRequestOperationCollectionValve.invoke(HttpRequestOperationCollectionValve.java:98)
    at org.apache.catalina.connector.CoyoteAdapter.service(CoyoteAdapter.java:407)
    at org.apache.coyote.http11.AbstractHttp11Processor.process(AbstractHttp11Processor.java:1001)
    at org.apache.coyote.AbstractProtocol$AbstractConnectionHandler.process(AbstractProtocol.java:585)
    at org.apache.tomcat.util.net.JIoEndpoint$SocketProcessor.run(JIoEndpoint.java:310)
    at java.util.concurrent.ThreadPoolExecutor$Worker.runTask(ThreadPoolExecutor.java:886)
    at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:908)
    at java.lang.Thread.run(Thread.java:680)

I you can see, I am trying to use pure JPA and only using Hibernate as a JPA provider.

I understand that the exception is caused by the session being detached from the entity. But, I thought that wouldn't happen if we are currently in a transaction, which should be the case since the logDOI method is annotated with @Transactional.

Of course, everything works perfectly if I change the FetchType to EAGER but it seems that I shouldn't have to do that.

I am also aware of OpenEntityManagerInViewFilter but it seems that I shouldn't have to use that either if I keep all access to my entities in a DAO annotated with @Transactional (or through some other means that I'm not aware of).

I think that I might be approaching this problem incorrectly but I don't know what the correct approach is. How is one supposed to effectively use lazily loaded properties?

Answer 1

Thanks to Shailendra I started to look closely at the transaction and noticed that the transaction was never starting. With that information I did some investigation and found this: Spring @Transaction not starting transactions. I put <tx:annotation-driven/> in my servlet-context.xml file and suddenly the transaction for logDOI started up and everything worked correctly; I no longer got the LazyInitializationException. I am not at all clear as to why that worked. Any information on that would be appreciated.

Update:

I figured it out. A critical piece of my problem was in the servlet-context.xml file. This is what it looked like

<?xml version="1.0" encoding="UTF-8"?>
<beans:beans xmlns="http://www.springframework.org/schema/mvc"
    xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
    xmlns:beans="http://www.springframework.org/schema/beans"
    xmlns:context="http://www.springframework.org/schema/context"
    xmlns:tx="http://www.springframework.org/schema/tx"
    xsi:schemaLocation="http://www.springframework.org/schema/mvc http://www.springframework.org/schema/mvc/spring-mvc-3.1.xsd
        http://www.springframework.org/schema/tx http://www.springframework.org/schema/tx/spring-tx-3.1.xsd
        http://www.springframework.org/schema/beans http://www.springframework.org/schema/beans/spring-beans-3.1.xsd
        http://www.springframework.org/schema/context http://www.springframework.org/schema/context/spring-context-3.1.xsd">

    <!-- DispatcherServlet Context: defines this servlet's request-processing infrastructure -->

    <!-- Enables the Spring MVC @Controller programming model -->
    <annotation-driven />

    <!-- Handles HTTP GET requests for /resources/** by efficiently serving up static resources in the ${webappRoot}/resources directory -->
    <resources mapping="/resources/**" location="/resources/" />

    <!-- Resolves views selected for rendering by @Controllers to .jsp resources in the /WEB-INF/views directory -->
    <beans:bean class="org.springframework.web.servlet.view.InternalResourceViewResolver">
        <beans:property name="prefix" value="/WEB-INF/views/" />
        <beans:property name="suffix" value=".jsp" />
    </beans:bean>

    <context:component-scan base-package="org.myapp.doi" />

</beans:beans>

The major problem was in that context:component-scan line. Spring MVC creates two context which beans are instantiated in: the root application context defined with the contextConfigLocation parameter in the web.xml file and the servlet context defined in the DispatcherServlet in the web.xml file. The servlet context could see the application context but not the other way around. Now, as a result of context:component-scan being defined in the servlet context and scanning the entire application namespace, my DAO was being instantiated in the servlet context. However, the transaction annotation scanning was being done in the application context and the AOP proxy stuff for it could not be done from there. Simply modifying the context:component-scan in the servlet context to scan only the MVC controllers (<context:component-scan base-package="org.myapp.doi.web" /> fixed everything; the DAO was being created in the application context and properly setup for transactions.

Answer 2

The best way to solve this would be to first understand why and when the session is closed inspite of being under single transaction. And the best way for that would be to enable the hibernate (as you are using hibernate as JPA provider) logging level to DEBUG in log4j configuration and track where the sessions are closed. This would give you a clear picture. Although the stack trace suggests that the underlying session was closed but there are obviously no reason why ? You can post the relevant debug/info messages logged.

Also you can set up logging for spring framework to track the transaction management infrastructure

The logs give fairly good messages on when the underlying session was closed and transaction committed.

For e.g.,

opened session at timestamp: 13476520251
............
...........
after transaction begin
..............

select x,y,z from......
...............
...commit
..........
..flushing session
..after transaction completion
..closing session