Hibernate的get和load的区别

　　　　　　　session = HibernateUtil.openSession();
            /*
             * 通过load的方式加载对象时，会使用延迟加载机制，此时并不会发出sql语句，只有当我们需要使用的时候才会从数据库中去查询
             */
            User user = (User)session.load(User.class, 2);

　　　　　　session = HibernateUtil.openSession();
　　　　　　User user = (User)session.load(User.class, 2);
　　　　　　System.out.println(user);

Hibernate: select user0_.id as id0_0_, user0_.username as username0_0_, user0_.password as password0_0_, user0_.born as born0_0_ from user user0_ where user0_.id=?
User [id=2, username=aaa, password=111, born=2013-10-16 00:14:24.0]

　　　　　　session = HibernateUtil.openSession();
            /*
             * 通过load的方式加载对象时，会使用延迟加载机制，此时得到的User对象其实是一个
             * 代理对象，该代理对象里面仅仅只有id这个属性
             */
            User user = (User)session.load(User.class, 2);
            System.out.println(user.getId());

　　　　　　console:　　2

            session = HibernateUtil.openSession();
            /*
             * 通过load的方式加载对象时，会使用延迟加载机制，此时得到的User对象其实是一个
             * 代理对象，该代理对象里面仅仅只有id这个属性
             */
            User user = (User)session.load(User.class, 2);
            System.out.println(user.getId());
            // 如果此时要得到user其他属性，则会从数据库中查询
            System.out.println(user.getUsername());            

2
Hibernate: select user0_.id as id0_0_, user0_.username as username0_0_, user0_.password as password0_0_, user0_.born as born0_0_ from user user0_ where user0_.id=?
aaa

　　　　　　　session = HibernateUtil.openSession();
            /*
             * 通过get方法来加载对象时，不管使不使用该对象，都会发出sql语句，从数据库中查询
             */
            User user = (User)session.get(User.class, 2);

Hibernate: select user0_.id as id0_0_, user0_.username as username0_0_, user0_.password as password0_0_, user0_.born as born0_0_ from user user0_ where user0_.id=?

　　　　　　  session = HibernateUtil.openSession();
            /*
             * 当通过get方式试图得到一个id不存在的user对象时，此时会报NullPointException异常
             */
            User user = (User)session.get(User.class, 20);
            System.out.println(user.getUsername());

Hibernate: select user0_.id as id0_0_, user0_.username as username0_0_, user0_.password as password0_0_, user0_.born as born0_0_ from user user0_ where user0_.id=?
java.lang.NullPointerException　　.........

　　　　　　session = HibernateUtil.openSession();
            /*
             * 当通过get方式试图得到一个id不存在的user对象时，此时会报ObjectNotFoundException异常
             */
            User user = (User)session.load(User.class, 20);
            System.out.println(user.getId());
            System.out.println(user.getUsername());

20
Hibernate: select user0_.id as id0_0_, user0_.username as username0_0_, user0_.password as password0_0_, user0_.born as born0_0_ from user user0_ where user0_.id=?
org.hibernate.ObjectNotFoundException: No row with the given identifier exists: [com.xiaoluo.bean.User#20]......

public class UserDAO
{
    public User loadUser(int id)
    {
        Session session = null;
        Transaction tx = null;
        User user =  null;
        try
        {
            session = HibernateUtil.openSession();
            tx = session.beginTransaction();
            user = (User)session.load(User.class, 1);
            tx.commit();
        }
        catch (Exception e)
        {
            e.printStackTrace();
            tx.rollback();
        }
        finally
        {
            HibernateUtil.close(session);
        }
        return user;
    }
}

　　@Test
    public void testLazy06()
    {
        UserDAO userDAO = new UserDAO();
        User user = userDAO.loadUser(2);
        System.out.println(user);
    }

org.hibernate.LazyInitializationException: could not initialize proxy - no Session　　.............