could not initialize proxy - no Session

org.hibernate.LazyInitializationException: could not initialize proxy - no Session
    at org.hibernate.proxy.AbstractLazyInitializer.initialize(AbstractLazyInitializer.java:132)
    at org.hibernate.proxy.AbstractLazyInitializer.getImplementation(AbstractLazyInitializer.java:174)
    at org.hibernate.proxy.pojo.javassist.JavassistLazyInitializer.invoke(JavassistLazyInitializer.java:190)

org.hibernate.LazyInitializationException: could not initialize proxy - no Session
	at org.hibernate.proxy.AbstractLazyInitializer.initialize(AbstractLazyInitializer.java:132)
	at org.hibernate.proxy.AbstractLazyInitializer.getImplementation(AbstractLazyInitializer.java:174)
	at org.hibernate.proxy.pojo.javassist.JavassistLazyInitializer.invoke(JavassistLazyInitializer.java:190)

 

出现这种异常的本质原因是有点诡异，hibernate在获取一个Entity的时候，第一步获取到是Entity的Proxy. 如果仅仅在获取到Proxy以后Session就关闭的话，就会出现这个异常。在Hibernate3.0中，Entity的Proxy与真实实体之间默认是lazy loading的，如果在一个transaction仅仅获取了一下Entity的Proxy，然后transaction就commit， 这个时候也会出现上述异常。

 

譬如我们喜欢在Manager(Service)层上加上Transaction

 

@Service("userManager")
@Transactional
public class UserManager extends BaseManager{

    public User getUserById(long id){
        User user = userDao.get(id);
        return user;
    }

}

@Service("userManager")
@Transactional
public class UserManager extends BaseManager{
	
	public User getUserById(long id){
		User user = userDao.get(id);
		return user;
	}
	
}

这个时候拿到的其实是User实体的Proxy，结果在方法的最后提交transaction时就会有此异常。

解决方案：

1. 在Hibernate Mapping文件中设置实体的lazy="false"

2. 或者主动访问一下Entity属性, 迫使Proxy加载具体实体数据。

 

@Service("userManager")
@Transactional
public class UserManager extends BaseManager{

    public User getUserById(long id){
        User user = userDao.get(id);
        user.getName();
        return user;
    }

}