我试图将对象保存到数据库，但它没有保存到数据库中。

用户详细信息.java

import javax.persistence.Column;
import javax.persistence.Entity;
import javax.persistence.GeneratedValue;
import javax.persistence.Id;
import javax.persistence.Table;

@Entity
@Table(name="USER_DETAILS")
public class UserDetails {

    @Id @GeneratedValue()
    @Column(name="USER_ID")
    private int userId;

    @Column(name="USER_NAME")
    private String userName;

    //...getter and setters

}

应用程序.java

public class App {

    public static void main(String[] args) {
        UserDetails user = new UserDetails();
        user.setUserName("abc");

        SessionFactory factory = new Configuration().configure().buildSessionFactory();
        Session session = factory.openSession();

        Object o = session.save(user);
        System.out.println("User saved with id - " +o);
        System.out.println("HashCode of session 1st "+session.hashCode());
        session.close();

        session = factory.openSession();
        System.out.println("HashCode of session 2nd "+session.hashCode());

        UserDetails user1 =(UserDetails)session.get(UserDetails.class,Integer.valueOf(o.toString()));
        System.out.println(user1.getUserName());

        session.close();


    }
}

记录档：

Hibernate: insert into USER_DETAILS (USER_ID, USER_NAME) values (default, ?)
Hibernate: values identity_val_local()
User saved with id - 1
HashCode of session 1st 9299042
HashCode of session 2nd 12206609
Hibernate: select userdetail0_.USER_ID as USER1_0_0_, userdetail0_.USER_NAME as USER2_0_0_ from USER_DETAILS userdetail0_ where userdetail0_.USER_ID=?
abc

我没有使用事务，我知道如果我将session.save代码放在session.beginTransaction（）和session.getTransaction（）.commit（）中，数据将保存在数据库中。但由于我也在执行session.get，我在执行www.example.com（）时获得了IDsession.save，我如何取回对象？
如果是一级缓存，那么如何..因为我也在关闭会话并打开一个新会话。我也没有配置任何二级缓存。
请提供宝贵的意见。