public class UserAction extends ActionSupport {

    private User user;

    private UserDao userDao;
    
    public User getUser() {
        return user;
    }

    public void setUser(User user) {
        this.user = user;
    }
    
    public String save() {
        userDao.save(user);
        return SUCCESS;
    }

    public void setUserDao(UserDao userDao) {
        this.userDao = userDao;
    }

public class User implements Serializable {
    private static final long serialVersionUID = -966101986208807450L;
    
    private Long userId;
    private String userName;




    public User() {
    }


    public Long getUserId() {
        return userId;
    }

    public void setUserId(Long userId) {
        this.userId = userId;
    }

    public String getUserName() {
        return userName;
    }

    public void setUserName(String userName) {
        this.userName = userName;
    }    
}

JSP上写一个hidden
<hidden name="user.userId" value="${user.userId}"/>

------解决方案--------------------
不是hibernate的问题.是struts.xml配置与springContext.xml两个关联的配置问题...就是你的userDao没有被注入进对象...把这两个配置文件贴来看下...

------解决方案--------------------
com.ylzinfo.msw.app.domain.User$$EnhancerByCGLIB$$64c0be74

userDao.save(user);org.hibernate.MappingException: Unknown entity

其中user是得对象不认识，debug看看user里面到底是什么