SpringMVC中Model与Session的区别说明

@Controller
@SessionAttributes("user")
public class LoginController {
    @Autowired
    private LoginService loginService;
    
    //表单提交过来的路径
    @RequestMapping("/checkLogin")
    //@ModelAttribute
    public String checkLogin(@ModelAttribute("abc")User user,Model model){
        //调用service方法
        user = loginService.checkLogin(user.getUsername(), user.getPassword());
        //若有user则添加到model里并且跳转到首页页面
        if(user != null){
            model.addAttribute("user",user);
            return "redirect:/user/index.do";
        }
        return "login";
    }    
    
    //注销方法
    @RequestMapping("/outLogin")
    public String outLogin(HttpSession session,SessionStatus sessionStatus){
        //通过session.invalidata()方法来注销当前的session
     sessionStatus.setComplete();
        //session.invalidate();
        //session.removeAttribute("user");
        return "redirect:/checkLogin.do";
    }
}

<%-- 测试能够获取session
<div>
<strong> ${sessionScope.user.username}!!!!! </strong>
<strong> ${user.username}????? </strong>
</div> 
--%>
<c:choose>
<c:when test="${!empty user.username}">
<li class="dropdown"><a href="#" rel="external nofollow"  class="dropdown-toggle"
data-toggle="dropdown">${user.username} <strong
class="caret"></strong></a>
<ul class="dropdown-menu">
<li><a href="<%=request.getContextPath() %>/user/toUserDetail.do?id=${user.id}" rel="external nofollow" >个人信息</a></li>
<li class="divider"></li>
<li><a href="<%=request.getContextPath() %>/outLogin.do" rel="external nofollow" >退出</a></li>
</ul></li>
</c:when>
<c:otherwise>
<li><a href="<%=request.getContextPath() %>/user/toLogin.do" rel="external nofollow" >登录</a>
<li><a href="<%=request.getContextPath() %>/user/toRegedit.do" rel="external nofollow" >注册</a>
</c:otherwise>
</c:choose>

@Service
public class LoginServiceImpl implements LoginService{
 @Autowired
 private UserMapper userMapper;
 @Override
 public User checkLogin(String username, String password) {
  User user = userMapper.findByUsername(username);
        if(user != null && user.getPassword().equals(password)){        
            return user;
        }
        return null;
 } 
}