解释一个关于Hibernate lazy的问题

2022-07-15 80酷酷网 80kuku.com

　　问题

使用Hibernate时意外报错:

Exception in thread "main" org.hibernate.LazyInitializationException: could not initialize proxy - the owning Session was closed at org.hibernate.proxy.AbstractLazyInitializer.initialize(AbstractLazyInitializer.java:53) at org.hibernate.proxy.AbstractLazyInitializer.getImplementation(AbstractLazyInitializer.java:84) at org.hibernate.proxy.CGLIBLazyInitializer.intercept(CGLIBLazyInitializer.java:134) at com.entry.database.bean.OaLoginLink$EnhancerByCGLIB$a418b18d.getName(<generated>) at test.Test.main(Test.java:145)

很是让我头痛,上网查看相关资料发现这样一个解决方式:

"org.hibernate.LazyInitializationException: could not initialize proxy"延迟抓取出的错,hb3对many-to-one的默认处理是lazy = "proxy"，没有搞懂到底怎么回事，把所有many-to-one,one-to-one都加上lazy="false"...

这个方法理论上没错,但是会让人产生误解,使人以为只是修改<set>中的lazy值,照做后程序依然会报错,看看下面的文章也许就明白了(注意最后一行红色标记)!

lazy initialization
集合(不包括数组)是可以延迟初始化的,意思是仅仅当应用程序需要访问时，才载入他们的值。
s = sessions.openSession();
User u = (User) s.find("from User u where u.name=?", userName,
Hibernate.STRING).get(0);
Map permissions = u.getPermissions();
s.connection().commit();
s.close();
Integer accessLevel = (Integer) permissions.get("accounts"); //Error!
因为在commit之前,permissions没有被用到,permission没有被初始化,而session被close了,导致permissions永远都无法load data.
解决办法:吧最后一行一道session被提交之前.
设置:
<set name="names" table="NAMES" lazy="true" order-by="name asc">
<key column="group_id"/>
<element column="NAME" type="string"/>
</set>

==================================

在做Spring1.2 + Hibernate 3 + struts demo时候遇到一个问题，编辑用户数据时候

用com.jeedev.service.dao.hibernate.UserHibernateDao 中 public TSysuser getUser(int userid) { } 方法，总是不能正常显示编辑数据。具体表现为：

参考 com.jeedev.service.dao.hibernate.UserHibernateDao 第32-45行

java代码:

public TSysuser getUser(int userid) {

if (this.getHibernateTemplate() == null) {
System.out.println("error at there");
return null;
}

TSysuser edituser= (TSysuser) getHibernateTemplate().load(TSysuser.class, new Integer(userid));

System.out.println(edituser.getUsername());
System.out.println(edituser.getDeptno());

return edituser;
}

如果删除上面的
java代码:
System.out.println(edituser.getUsername());
System.out.println(edituser.getDeptno());

在点击编号，修改时候就会出现错误：

2005-10-27 15:35:59,245 ERROR [org.hibernate.LazyInitializationException] - could not initialize proxy - the owning Session was closed
org.hibernate.LazyInitializationException: could not initialize proxy - the owning Session was closed

经过在javaeye论坛大家一致认为是hibernate lazy的原因

在WEB级别应用时候，会出现意想不到的lazy错误，解决方法就是设置 lazy="false" 例：

<hibernate-mapping>