我知道这个问题在这里和互联网上已被多次询问,我已经阅读了很多这些答案,但我仍然不明白解决这个问题的正确方法。我正在尝试使用Spring MVC和JPA,每次访问一个延迟加载的属性时,我都会得到一个LazyInitializationException。
以下是我正在尝试的一些代码:
@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());
}
}
}
我正在访问的实体:
@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
}
从DOI引用的实体
@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;
}
}
Spring MVC控制器:
@Controller
@RequestMapping("/summary")
public class DOISummaryController {
@Autowired
MyDAO myDAO;
@RequestMapping()
public String DOISummary() {
myDAO.logDOI();
return "home";
}
}
My Spring配置:
<?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>
根据要求进行堆栈跟踪:
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)
我可以看到,我正在尝试使用纯JPA并仅使用Hibernate作为JPA提供程序。
我理解异常是由会话与实体分离引起的。但是,我认为如果我们目前处于一个事务中就不会发生这种情况,因为logDOI方法是用@Transactional注释的。
当然,如果我将FetchType更改为EAGER,一切都会完美,但似乎我不应该这样做。
我也知道OpenEntityManagerInViewFilter但似乎我不应该使用它,如果我在使用@Transactional注释的DAO中保留对我的实体的所有访问权限(或者通过我不知道的其他方式) )。
我认为我可能会错误地解决这个问题,但我不知道正确的方法是什么。如何有效地使用延迟加载的属性?
答案 0 :(得分:18)
感谢Shailendra,我开始密切关注交易,并注意到交易从未开始。有了这些信息,我做了一些调查,发现了这个:Spring @Transaction not starting transactions。我将<tx:annotation-driven/>
放在我的servlet-context.xml文件中,然后突然启动了logDOI的事务,一切正常;我不再得到LazyInitializationException。我一点也不清楚为什么这样有效。有关这方面的任何信息将不胜感激。
更新
我明白了。我的问题的一个关键部分是在servlet-context.xml文件中。这就是它的样子
<?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>
主要问题在于上下文:组件扫描线。 Spring MVC创建两个bean实例化的上下文:使用web.xml文件中的contextConfigLocation参数定义的根应用程序上下文,以及web.xml文件中DispatcherServlet中定义的servlet上下文。 servlet上下文可以看到应用程序上下文,但不是相反。现在,作为上下文的结果:在servlet上下文中定义组件扫描并扫描整个应用程序命名空间,我的DAO正在servlet上下文中实例化。但是,事务注释扫描正在应用程序上下文中完成,并且AOP代理程序无法从那里完成。只需修改上下文:servlet上下文中的组件扫描仅扫描MVC控制器(<context:component-scan base-package="org.myapp.doi.web" />
修复所有内容; DAO正在应用程序上下文中创建并正确设置事务。
答案 1 :(得分:3)
解决这个问题的最佳方法是首先了解会议结束的原因和时间,尽管是单一交易。最好的方法是在log4j配置中启用hibernate(当你使用hibernate作为JPA提供程序时)将日志级别设置为DEBUG并跟踪会话关闭的位置。这会给你一个清晰的画面。虽然堆栈跟踪表明底层会话已关闭,但显然没有理由?您可以发布记录的相关调试/信息消息。
您还可以设置spring框架的日志记录以跟踪事务管理基础结构
日志会在基础会话关闭和事务提交时提供相当好的消息。
例如,
opened session at timestamp: 13476520251
............
...........
after transaction begin
..............
select x,y,z from......
...............
...commit
..........
..flushing session
..after transaction completion
..closing session
答案 2 :(得分:1)
我也遇到了这个问题,但是在你的回答的启发下,我解决了这个问题。就是这样。
我的应用程序尝试使用Jpa Repository来处理休息控制器中的数据,结果发现没有会话错误。这是代码:
@RequestMapping(value = "/create", method = POST, consumes = MediaType.APPLICATION_JSON_VALUE)
public ResponseEntity<Void> create(@RequestBody Map<String, Object> params) {
Project project = Factory.project().build(params);
project = repository.save(project);
return ResponseEntity.ok().build();
}
根据这个post和这个post,我们知道servlet上下文中的bean可以引用应用程序上下文中的bean。因此TransactionManager无法访问此rest控制器bean,从而导致此错误。
解决方案,在rest controller和repository之间创建一个中间层bean应用程序上下文,封装这些代码。我试试,它工作正常。稍后更新代码。