Hibernate/Spring:懒得初始化 - 没有关闭会话或会话

Question

Hibernate/Spring:懒得初始化 - 没有关闭会话或会话

Nik*_*iko 38 java spring hibernate lazy-loading

对于答案,请向下滚动到此结尾...

基本问题与多次询问相同.我有一个简单的程序,有两个POJO事件和用户 - 用户可以有多个事件.

@Entity
@Table
public class Event {
 private Long id;
 private String name;
 private User user;

 @Column
 @Id
 @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;}

 @ManyToOne
 @JoinColumn(name="user_id")
 public User getUser() {return user;}
 public void setUser(User user) {this.user = user;}

}

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用户:

@Entity
@Table
public class User {
 private Long id;
 private String name;
 private List<Event> events;

 @Column
 @Id
 @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; }

 @OneToMany(mappedBy="user", fetch=FetchType.LAZY)
 public List<Event> getEvents() { return events; }
 public void setEvents(List<Event> events) { this.events = events; }

}

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注意:这是一个示例项目.我真的想在这里使用Lazy抓取.

现在我们需要配置spring和hibernate,并有一个简单的basic-db.xml用于加载:


<?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:aop="http://www.springframework.org/schema/aop"
       xsi:schemaLocation="http://www.springframework.org/schema/beans 
           http://www.springframework.org/schema/beans/spring-beans-3.0.xsd
           http://www.springframework.org/schema/aop 
           http://www.springframework.org/schema/aop/spring-aop-3.0.xsd">


 <bean id="myDataSource" class="org.apache.commons.dbcp.BasicDataSource"
  destroy-method="close"  scope="thread">
  <property name="driverClassName" value="com.mysql.jdbc.Driver" />
  <property name="url" value="jdbc:mysql://192.168.1.34:3306/hibernateTest" />
  <property name="username" value="root" />
  <property name="password" value="" />
  <aop:scoped-proxy/>
 </bean>

 <bean class="org.springframework.beans.factory.config.CustomScopeConfigurer">
  <property name="scopes">
   <map>
    <entry key="thread">
     <bean class="org.springframework.context.support.SimpleThreadScope" />
    </entry>
   </map>
  </property>
 </bean>

 <bean id="mySessionFactory"
  class="org.springframework.orm.hibernate3.annotation.AnnotationSessionFactoryBean" scope="thread">
  <property name="dataSource" ref="myDataSource" />
  <property name="annotatedClasses">
   <list>
    <value>data.model.User</value>
    <value>data.model.Event</value>
   </list>
  </property>
  <property name="hibernateProperties">
   <props>
    <prop key="hibernate.dialect">org.hibernate.dialect.MySQLDialect</prop>
    <prop key="hibernate.show_sql">true</prop>
    <prop key="hibernate.hbm2ddl.auto">create</prop>
   </props>
  </property>
  <aop:scoped-proxy/>

 </bean>

 <bean id="myUserDAO" class="data.dao.impl.UserDaoImpl">
  <property name="sessionFactory" ref="mySessionFactory" />
 </bean>

 <bean id="myEventDAO" class="data.dao.impl.EventDaoImpl">
  <property name="sessionFactory" ref="mySessionFactory" />
 </bean>

</beans>

注意:我使用了CustomScopeConfigurer和SimpleThreadScope,但这并没有改变任何东西.

我有一个简单的dao-impl(只粘贴userDao - EventDao几乎相同 - 除了没有"listWith"函数:


public class UserDaoImpl implements UserDao{

 private HibernateTemplate hibernateTemplate;

 public void  setSessionFactory(SessionFactory sessionFactory) {
  this.hibernateTemplate = new HibernateTemplate(sessionFactory);

 }

 @SuppressWarnings("unchecked")
 @Override
 public List listUser() {
  return hibernateTemplate.find("from User");
 }

 @Override
 public void saveUser(User user) {
  hibernateTemplate.saveOrUpdate(user);

 }

 @Override
 public List listUserWithEvent() {

  List users = hibernateTemplate.find("from User");
  for (User user : users) {
   System.out.println("LIST : " + user.getName() + ":");
   user.getEvents().size();
  }
  return users;
 }

}

我收到了org.hibernate.LazyInitializationException - 无法懒惰地初始化一个角色集合:data.model.User.events,没有会话或会话在user.getEvents()的行中关闭.size () ;

最后但并非最不重要的是我使用的Test类:


public class HibernateTest {

 public static void main(String[] args) {

  ClassPathXmlApplicationContext ac = new ClassPathXmlApplicationContext("basic-db.xml");


  UserDao udao = (UserDao) ac.getBean("myUserDAO");
  EventDao edao = (EventDao) ac.getBean("myEventDAO");


  System.out.println("New user...");
  User user = new User();
  user.setName("test");

  Event event1 = new Event();
  event1.setName("Birthday1");
  event1.setUser(user);

  Event event2 = new Event();
  event2.setName("Birthday2");
  event2.setUser(user);

  udao.saveUser(user);
  edao.saveEvent(event1);
  edao.saveEvent(event2);

  List users = udao.listUserWithEvent();
  System.out.println("Events for users");
  for (User u : users) {

   System.out.println(u.getId() + ":" + u.getName() + " --");
   for (Event e : u.getEvents())
   {
    System.out.println("\t" + e.getId() + ":" + e.getName());
   }
  }

  ((ConfigurableApplicationContext)ac).close();
 }

}

这是例外:

1621 [main] ERROR org.hibernate.LazyInitializationException - failed to lazily initialize a collection of role: data.model.User.events, no session or session was closed
org.hibernate.LazyInitializationException: failed to lazily initialize a collection of role: data.model.User.events, 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.readSize(AbstractPersistentCollection.java:119)
 at org.hibernate.collection.PersistentBag.size(PersistentBag.java:248)
 at data.dao.impl.UserDaoImpl.listUserWithEvent(UserDaoImpl.java:38)
 at HibernateTest.main(HibernateTest.java:44)
Exception in thread "main" org.hibernate.LazyInitializationException: failed to lazily initialize a collection of role: data.model.User.events, 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.readSize(AbstractPersistentCollection.java:119)
 at org.hibernate.collection.PersistentBag.size(PersistentBag.java:248)
 at data.dao.impl.UserDaoImpl.listUserWithEvent(UserDaoImpl.java:38)
 at HibernateTest.main(HibernateTest.java:44)

事情尝试但没有奏效:

分配一个threadScope并使用beanfactory(我使用"请求"或"线程" - 没有注意到差异):

  // scope stuff
  Scope threadScope = new SimpleThreadScope();
  ConfigurableListableBeanFactory beanFactory = ac.getBeanFactory();
  beanFactory.registerScope("request", threadScope);
  ac.refresh();
...

通过从deo获取会话对象来设置事务:

...
  Transaction tx = ((UserDaoImpl)udao).getSession().beginTransaction();
  tx.begin();
  users = udao.listUserWithEvent();
...

在listUserWithEvent()中获取事务

 public List listUserWithEvent() {
  SessionFactory sf = hibernateTemplate.getSessionFactory();
  Session s = sf.openSession();
  Transaction tx = s.beginTransaction();
  tx.begin();

  List users = hibernateTemplate.find("from User");
  for (User user : users) {
   System.out.println("LIST : " + user.getName() + ":");
   user.getEvents().size();
  }
  tx.commit();
  return users;
 }

我现在真的没有想法了.另外,使用listUser或listEvent工作正常.

向前一步:

感谢蒂埃里,我更进了一步(我想).我创建了MyTransaction类并在那里完成了我的整个工作,从春天开始获取所有内容.新的主要看起来像这样:


 public static void main(String[] args) {

  ClassPathXmlApplicationContext ac = new ClassPathXmlApplicationContext("basic-db.xml");

  // getting dao
  UserDao udao = (UserDao) ac.getBean("myUserDAO");
  EventDao edao = (EventDao) ac.getBean("myEventDAO");

  // gettting transaction template
  TransactionTemplate transactionTemplate = (TransactionTemplate) ac.getBean("transactionTemplate");

  MyTransaction mt = new MyTransaction(udao, edao);
  transactionTemplate.execute(mt);

  ((ConfigurableApplicationContext)ac).close();
 }

不幸的是现在有一个空指针Exception @:user.getEvents().size(); (在daoImpl中).

我知道它不应该是null(既不是来自控制台的输出也不是来自db布局).

这是控制台输出以获取更多信息(我检查了user.getEvent()== null并打印了"EVENT为NULL"):

New user...
Hibernate: insert into User (name) values (?)
Hibernate: insert into User (name) values (?)
Hibernate: insert into Event (name, user_id) values (?, ?)
Hibernate: insert into Event (name, user_id) values (?, ?)
Hibernate: insert into Event (name, user_id) values (?, ?)
List users:
Hibernate: select user0_.id as id0_, user0_.name as name0_ from User user0_
1:User1
2:User2
List events:
Hibernate: select event0_.id as id1_, event0_.name as name1_, event0_.user_id as user3_1_ from Event event0_
1:Birthday1 for 1:User1
2:Birthday2 for 1:User1
3:Wedding for 2:User2
Hibernate: select user0_.id as id0_, user0_.name as name0_ from User user0_
Events for users
1:User1 --
EVENT is NULL
2:User2 --
EVENT is NULL

您可以从http://www.gargan.org/code/hibernate-test1.tgz获取示例项目(这是一个eclipse/maven项目)

解决方案(用于控制台应用)

这个问题实际上有两个解决方案 - 取决于您的环境:

对于控制台应用程序,您需要一个事务模板,该模板捕获actutal db逻辑并负责事务:


public class UserGetTransaction implements TransactionCallback{

 public List users;

 protected ApplicationContext context;

 public UserGetTransaction (ApplicationContext context) {
  this.context = context;
 }

 @Override
 public Boolean doInTransaction(TransactionStatus arg0) {
  UserDao udao = (UserDao) ac.getBean("myUserDAO");
  users = udao.listUserWithEvent();
  return null;
 }

}

您可以通过以下方式使用此方法


 TransactionTemplate transactionTemplate = (TransactionTemplate) context.getBean("transactionTemplate");
 UserGetTransaction mt = new UserGetTransaction(context);
 transactionTemplate.execute(mt);

为了使其工作,您需要为spring定义模板类(即在basic-db.xml中):

<bean id="transactionTemplate" class="org.springframework.transaction.support.TransactionTemplate">
    <property name="transactionManager" ref="transactionManager"/>
</bean>

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另一种(可能的)解决方案

谢谢你

    PlatformTransactionManager transactionManager = (PlatformTransactionManager) applicationContext.getBean("transactionManager");
    DefaultTransactionAttribute transactionAttribute = new DefaultTransactionAttribute(TransactionDefinition.PROPAGATION_REQUIRED);

transactionAttribute.setIsolationLevel(TransactionDefinition.ISOLATION_SERIALIZABLE);
    TransactionStatus status = transactionManager.getTransaction(transactionAttribute);
    boolean success = false;
    try {
      new UserDataAccessCode().execute();
      success = true;
    } finally {
      if (success) {
        transactionManager.commit(status);
      } else {
        transactionManager.rollback(status);
      }
    }

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解决方案(针对servlet)

Servlet并不是一个大问题.当你有一个servlet时,你可以在函数开头简单地启动和绑定一个事务,并在最后解除绑定:

public void doGet(...) {
  SessionFactory sessionFactory = (SessionFactory) context.getBean("sessionFactory");
  Session session = SessionFactoryUtils.getSession(sessionFactory, true);
  TransactionSynchronizationManager.bindResource(sessionFactory, new SessionHolder(session));

// Your code....

  TransactionSynchronizationManager.unbindResource(sessionFactory);
}

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Answer 1

Thi*_*rry 26

我认为你不应该使用hibernate会话事务方法,但让spring做到这一点.

将此添加到您的spring conf:

<bean id="txManager" class="org.springframework.orm.hibernate3.HibernateTransactionManager">
    <property name="sessionFactory" ref="mySessionFactory" />
</bean>

<bean id="transactionTemplate" class="org.springframework.transaction.support.TransactionTemplate">
    <property name="transactionManager" ref="txManager"/>
</bean>

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然后我会修改你的测试方法以使用spring transaction模板:

public static void main(String[] args) {
    // init here (getting dao and transaction template)

    transactionTemplate.execute(new TransactionCallback() {
        @Override
        public Object doInTransaction(TransactionStatus status) {
          // do your hibernate stuff in here : call save, list method, etc
        }
    }
}

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作为旁注,默认情况下@OneToMany关联是惰性的,因此您不需要将其注释为惰性.(@*ToMany默认为LAZY,默认情况下@*ToOne为EAGER)

编辑:现在从hibernate的角度来看现在发生了什么:

开放会话(有交易开始)
保存用户并将其保留在会话中(将会话缓存视为实体hashmap,其中键是实体ID)
保存事件并将其保留在会话中
保存另一个事件并将其保留在会话中
...与所有保存操作相同......
然后加载所有用户("来自用户"查询)
那时hibernate看到它已经在会话中已经有了对象,所以丢弃它从请求中得到的那个并从会话中返回一个.
您的会话中的用户没有初始化其事件集合,因此您将获得null.
...

以下是一些增强代码的要点:

在您的模型中,当不需要收集订单时,请使用Set,而不是List的集合(私有Set事件,而不是私有List事件)
在你的模型中,键入你的集合,否则hibernate将不会获取哪个实体(私有Set <Event>事件)
当您设置双向关系的一侧,并且您希望在同一事务中使用关系的mappedBy端时,请设置两侧.在下一个tx之前,Hibernate不会为你做这件事(当会话是来自db状态的全新视图时).

因此,为了解决上述问题,要么在一个事务中进行保存,要么在另一个事务中进行加载:

public static void main(String[] args) {
    // init here (getting dao and transaction template)
    transactionTemplate.execute(new TransactionCallback() {
        @Override
        public Object doInTransaction(TransactionStatus status) {
          // save here
        }
    }

    transactionTemplate.execute(new TransactionCallback() {
        @Override
        public Object doInTransaction(TransactionStatus status) {
          // list here
        }
    }
}

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或设置双方:

...
event1.setUser(user);
...
event2.setUser(user);
...
user.setEvents(Arrays.asList(event1,event2));
...

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(另外不要忘记解决上面的代码增强点,Set not List,集合打字)

Answer 2

wee*_*ens 9

对于Web应用程序,还可以在web.xml中声明一个特殊的Filter,它将执行session-per-request:

<filter>
    <filter-name>openSessionInViewFilter</filter-name>
    <filter-class>org.springframework.orm.hibernate3.support.OpenSessionInViewFilter</filter-class>
</filter>

<filter-mapping>
    <filter-name>openSessionInViewFilter</filter-name>
    <url-pattern>/*</url-pattern>
</filter-mapping>

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之后,您可以在请求期间随时延迟加载数据.

Answer 3

小智 7

我来到这里寻找有关类似问题的提示.我尝试了Thierry提到的解决方案,但它没有用.之后,我尝试了这些线,它工作:

SessionFactory sessionFactory = (SessionFactory) context.getBean("sessionFactory");
Session session = SessionFactoryUtils.getSession(sessionFactory, true);
TransactionSynchronizationManager.bindResource(sessionFactory, new SessionHolder(session));

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事实上,我所做的是一个必须利用Spring存在经理/服务的批处理.在加载上下文并进行一些调用之后,我创建了一个着名的问题"未能懒惰地初始化集合".那3行为我解决了.

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