spring mvc @sessionattributes @ResponseBody 公用报错

[code="java"]

@Controller
@RequestMapping("/user")
@SessionAttributes(LoginConstants.CURRENT_USER)
public class UserContorller {
private UserService userService;
public UserService getUserService() {
return userService;
}

@Autowired
public void setUserService(UserService userService) {
    this.userService = userService;
}

@ResponseBody
@RequestMapping( value="login" ,method=RequestMethod.GET)
public String login(LoginForm loginForm,ModelMap modelMap){
    UserEntity userEntity = new UserEntity();
    userEntity.setName(loginForm.getName());
    userEntity.setPassword(loginForm.getPassword());
    userEntity = userService.login(userEntity);
    if(null != userEntity){//登录成功
        modelMap.addAttribute(LoginConstants.CURRENT_USER, userEntity);
        return "ok";
    }else{//登录失败 
        return "error";
    }
}

}
[/code]

报错如下错误：
[code="java"]
严重: Servlet.service() for servlet springmvc threw exception
java.lang.IllegalStateException: Cannot create a session after the response has been committed
at org.apache.catalina.connector.Request.doGetSession(Request.java:2400)
at org.apache.catalina.connector.Request.getSession(Request.java:2120)
at org.apache.catalina.connector.RequestFacade.getSession(RequestFacade.java:833)
[/code]

@ResponseBody

@RequestMapping( value="login" ,method=RequestMethod.GET)

public String login(LoginForm loginForm,ModelMap modelMap){

UserEntity userEntity = new UserEntity();

userEntity.setName(loginForm.getName());

userEntity.setPassword(loginForm.getPassword());

userEntity = userService.login(userEntity);

if(null != userEntity){//登录成功

modelMap.addAttribute(LoginConstants.CURRENT_USER, userEntity);

return "ok";

}else{//登录失败

return "error";

}

}
请将方法的参数加上该为public String login(HttpSession session, LoginForm loginForm,ModelMap modelMap)

你没有看到吗 在response的时候没有办法创建Session
if(null != userEntity){//登录成功

[color=red][b]在此处创建Session试试[/b][/color]
modelMap.addAttribute(LoginConstants.CURRENT_USER, userEntity);

return "ok";

}else{//登录失败

return "error";

}