我无法弄清楚为什么，但是Hibernate会话才应该关闭，所以我无法获取延迟加载的列表。
在日志中，它显示会话在DAO内的hibernateTemplate.findByNamedParam（）之后立即关闭。
当我运行我的网络应用时，我收到以下错误：
Mar 29, 2011 3:13:21 PM org.apache.catalina.core.StandardWrapperValve invoke
SEVERE: Servlet.service() for servlet [Spring MVC Dispatcher Servlet] in context with path [/apps] threw exception [Request processing failed; nested exception is org.hibernate.LazyInitializationException: failed to lazily initialize a collection of role: com.communitydriven.apps.entities.Project.tags, no session or session was closed] with root cause
org.hibernate.LazyInitializationException: failed to lazily initialize a collection of role: com.communitydriven.apps.entities.Project.tags, 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.iterator(PersistentBag.java:272)
at com.communitydriven.apps.managers.ProjectManager.getProject(ProjectManager.java:98)
at com.communitydriven.apps.controllers.ProjectController.getViewProject(ProjectController.java:86)
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.bind.annotation.support.HandlerMethodInvoker.invokeHandlerMethod(HandlerMethodInvoker.java:176)
at org.springframework.web.servlet.mvc.annotation.AnnotationMethodHandlerAdapter.invokeHandlerMethod(AnnotationMethodHandlerAdapter.java:426)
at org.springframework.web.servlet.mvc.annotation.AnnotationMethodHandlerAdapter.handle(AnnotationMethodHandlerAdapter.java:414)
at org.springframework.web.servlet.DispatcherServlet.doDispatch(DispatcherServlet.java:790)
at org.springframework.web.servlet.DispatcherServlet.doService(DispatcherServlet.java:719)
at org.springframework.web.servlet.FrameworkServlet.processRequest(FrameworkServlet.java:644)
at org.springframework.web.servlet.FrameworkServlet.doGet(FrameworkServlet.java:549)
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:304)
at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:210)
at org.springframework.web.filter.CharacterEncodingFilter.doFilterInternal(CharacterEncodingFilter.java:88)
at org.springframework.web.filter.OncePerRequestFilter.doFilter(OncePerRequestFilter.java:76)
at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:243)
at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:210)
at org.apache.catalina.core.StandardWrapperValve.invoke(StandardWrapperValve.java:240)
at org.apache.catalina.core.StandardContextValve.invoke(StandardContextValve.java:164)
at org.apache.catalina.authenticator.AuthenticatorBase.invoke(AuthenticatorBase.java:498)
at org.apache.catalina.core.StandardHostValve.invoke(StandardHostValve.java:164)
at org.apache.catalina.valves.ErrorReportValve.invoke(ErrorReportValve.java:100)
at org.apache.catalina.valves.AccessLogValve.invoke(AccessLogValve.java:562)
at org.apache.catalina.core.StandardEngineValve.invoke(StandardEngineValve.java:118)
at org.apache.catalina.connector.CoyoteAdapter.service(CoyoteAdapter.java:394)
at org.apache.coyote.http11.Http11Processor.process(Http11Processor.java:243)
at org.apache.coyote.http11.Http11Protocol$Http11ConnectionHandler.process(Http11Protocol.java:188)
at org.apache.coyote.http11.Http11Protocol$Http11ConnectionHandler.process(Http11Protocol.java:166)
at org.apache.tomcat.util.net.JIoEndpoint$SocketProcessor.run(JIoEndpoint.java:302)
at java.util.concurrent.ThreadPoolExecutor$Worker.runTask(ThreadPoolExecutor.java:886)
at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:908)
at java.lang.Thread.run(Thread.java:619)
我的道：
@Repository
public class ProjectDao implements IProjectDao {
private HibernateTemplate hibernateTemplate;
@Autowired
public void setSessionFactory(SessionFactory sessionFactory) {
this.hibernateTemplate = new HibernateTemplate(sessionFactory);
}
...
/**
* {@inheritDoc}
*/
@Override
public Project getProject(Project project) {
// Validate required parameters
if ( (project.getId() == null) ) {
throw new NullPointerException("Missing required parameter: " +
project.toString());
}
// Parameters
List<String> paramNames = new ArrayList<String>();
List<Object> values = new ArrayList<Object>();
// Construct HQL
StringBuffer hql = new StringBuffer();
hql.append("from Project p ");
boolean whereUsed = false; // track of "where" clause has been used
// Filter by Id
if (project.getId() != null) {
whereUsed = DaoUtils.appendFilter(whereUsed, hql);
hql.append("p.id = :id ");
paramNames.add("id");
values.add(project.getId());
}
// Get list of matching projects
@SuppressWarnings("unchecked")
List<Project> projects =
hibernateTemplate.findByNamedParam(
hql.toString(),
paramNames.toArray(new String[paramNames.size()]),
values.toArray());
// Get unique result
Project projectResult = DataAccessUtils.uniqueResult(projects);
return projectResult;
}
}
我的经理：
@Component
public class ProjectManager implements IProjectManager {
@Autowired
private IProjectDao projectDao;
...
/**
* {@inheritDoc}
*/
@Transactional
@Override
public ProjectMO getProject(Long projectId) {
Project project = new Project();
project.setId(projectId);
project = projectDao.getProject(project);
ProjectMO projectMO = new ProjectMO();
projectMO.setId(project.getId());
projectMO.setName(project.getName());
projectMO.setDescription(project.getDescription());
StringBuffer tags = new StringBuffer();
final String DELIMITER = ", ";
for (Tag tag : project.getTags()) {
tags.append(tag.getName() + DELIMITER);
}
projectMO.setTags(tags.toString());
return projectMO;
}
}
实体：
@Entity
@Table
public class Project {
private Long id;
private String name;
private String description;
private User submittedBy;
private List<Tag> tags;
public String toString() {
final String DELIMITER = ", ";
StringBuffer sb = new StringBuffer();
sb.append(getClass().getName() + ": [");
sb.append("id: " + id).append(DELIMITER);
sb.append("name: " + name).append(DELIMITER);
sb.append("description: " + description).append("]");
return sb.toString();
}
// GETTERS AND SETTERS //
@Id
@Column
@GeneratedValue
public Long getId() {
return id;
}
public void setId(Long id) {
this.id = id;
}
@Column
public String getName() {
return name;
}
public void setName(String name) {
this.name = name;
}
@Column
public String getDescription() {
return description;
}
public void setDescription(String description) {
this.description = description;
}
@OneToOne
@JoinColumn
public User getSubmittedBy() {
return submittedBy;
}
public void setSubmittedBy(User submittedBy) {
this.submittedBy = submittedBy;
}
@ManyToMany
@JoinTable(name="Projects_Tags",
joinColumns={@JoinColumn(name="project_id")},
inverseJoinColumns={@JoinColumn(name="tag_id")})
public List<Tag> getTags() {
return tags;
}
public void setTags(List<Tag> tags) {
this.tags = tags;
}
}
我的数据库上下文：
<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:tx="http://www.springframework.org/schema/tx"
xsi:schemaLocation="
http://www.springframework.org/schema/beans http://www.springframework.org/schema/beans/spring-beans-3.0.xsd
http://www.springframework.org/schema/context http://www.springframework.org/schema/context/spring-context-3.0.xsd
http://www.springframework.org/schema/tx http://www.springframework.org/schema/tx/spring-tx-3.0.xsd">
<context:property-placeholder location="classpath:database.properties"/>
<bean id="dataSource"
class="org.springframework.jdbc.datasource.DriverManagerDataSource">
<property name="driverClassName" value="${jdbc.driverClassName}" />
<property name="url" value="${jdbc.url}" />
<property name="username" value="${jdbc.username}" />
<property name="password" value="${jdbc.password}" />
</bean>
<bean id="sessionFactory"
class="org.springframework.orm.hibernate3.annotation.AnnotationSessionFactoryBean">
<property name="dataSource" ref="dataSource"/>
<property name="hibernateProperties">
<value>
hibernate.dialect=org.hibernate.dialect.MySQLDialect
hibernate.hbm2ddl.auto=update
</value>
</property>
<property name="packagesToScan" value="com.communitydriven.apps.entities" />
</bean>
<tx:annotation-driven />
<bean id="transactionManager" class="org.springframework.orm.hibernate3.HibernateTransactionManager">
<property name="sessionFactory"><ref local="sessionFactory"/></property>
</bean>
</beans>
答案 0 :(得分：5)
您是否设置了OpenSessionInViewFilter？
答案 1 :(得分：4)
默认情况下，关联是延迟提取的。因此，一旦退出@Transactional注释的范围，就无法获得该集合。
虽然OpenSessionInViewFilter是一个选项，但我同意你的看法，这不是一个好方法。通常，您希望严格控制事务边界。
如果您知道您总是想要进行获取连接，只需将其包含在您的HQL中，或者在@ManyToMany中设置fetch = FetchType.EAGER。
如果你想在某些情况下包含标签而在其他情况下不包含标签，你可以在需要标签的情况下进行Hibernate.initialize（project.getTags（）），这将对标签进行单独的查询，但是它不是n + 1。或者，您可以有两个单独的HQL查询（一个包含提取连接，另一个不包含提取连接）。唯一的问题是，如果您有多个集合，则无法在多个集合上获取连接。所以Hibernate.initialize（）在这种情况下非常有用。
答案 2 :(得分：1)
您是否尝试过明确定义事务管理器实现，以及使用aspectj进行编织（因为您的注释是在具体类上）？
<bean id="transactionManager" class="org.springframework.orm.hibernate3.HibernateTransactionManager">
<property name="sessionFactory" ref="sessionFactory"/>
</bean>
<tx:annotation-driven transaction-manager="transactionManager" mode="aspectj" />
答案 3 :(得分：0)
什么是正在使用的事务管理器 - 它应该是HibernateTransactionManager或JTATransactionManager。
答案 4 :(得分：0)
我遇到了同样的问题，我不想将我的组件更改为服务，我也希望将@ManyToMany保留为FetchType.Lazy，因为它已多次调用并且不需要加入实体详细信息。所以我的脏解决方法是调用一个新实体而不是使用现有实体。请参阅我使用的示例:(假设您已在 DAO 中实现了 getProjectById 方法）
List<Tags> tags = projectDAO.getProjectById(project.getId()).getTags();
if(tags.size()>0)
for (Tag tag : ) {
tags.append(tag.getName() + DELIMITER);
}
)
而不是：
for (Tag tag : project.getTags()) {
tags.append(tag.getName() + DELIMITER);
}
)
答案 5 :(得分：0)
问题可能是由于在web.xml中定义的OpenViewSessionFilter中提供的映射，其中每个http会话都由hibernate会话绑定。
答案 6 :(得分：0)
我遇到了同样的问题。我的问题是我的servlet-context.xml和root-context.xml（我的申请上下文）
如果您在两个上下文中都指定了组件扫描，则可以通过更改来更正它 1.在servlet-context中，仅为控制器包指定component-scan 2.在根上下文中为其他包指定组件扫描（此处不包括控制器包）
我从这个答案得到了解决方案。您还可以参考该链接并了解@Transactional无效的原因
答案 7 :(得分：-2)
将ProjectManager类注释为@Service而不是@Component。