can someone explain how the controller class works - spring

Question

I am working on spring samples.I have a controller class named UserController2 as follows
#Controller
public class UserController2 extends MultiActionController {
private UserDAO userDAO;
public void setUserDAO(UserDAO userDAO) {
this.userDAO = userDAO;
}
#RequestMapping(params = "add", method = RequestMethod.POST)
public ModelAndView add(HttpServletRequest request,
HttpServletResponse response, User user) throws Exception {
userDAO.saveUser(user);
return new ModelAndView("redirect:User.htm");
}
public ModelAndView list(HttpServletRequest request,
HttpServletResponse response) throws Exception {
ModelMap modelMap = new ModelMap();
modelMap.addAttribute("userList", userDAO.listUser());
modelMap.addAttribute("User", new User());
return new ModelAndView("userForm", modelMap);
}
}
and i have a jsp page called userForm.jsp
<form:form method="POST" action="add.htm" commandName="User" modelAttribute="User">
<table>
<tr>
<td><form:label path="name">Name</form:label></td>
<td><form:input path="name" /></td>
</tr>
<tr>
<td><form:label path="id">id</form:label></td>
<td><form:input path="id" /></td>
</tr>
<tr>
<td><form:label path="password">Name</form:label></td>
<td><form:input path="password" /></td>
</tr>
<tr>
<td><form:label path="gender">Name</form:label></td>
<td><form:input path="gender" /></td>
</tr>
<tr>
<td><form:label path="gender">Name</form:label></td>
<td><form:input path="gender" /></td>
</tr>
<tr>
<td><form:label path="country">Name</form:label></td>
<td><form:input path="country" /></td>
</tr>
<tr>
<td colspan="2">
<input type="submit" value="Submit"/>
</td>
</tr>
</table>
</form:form>
what actually does the below codes returns
return new ModelAndView("userForm", modelMap);
and
return new ModelAndView("redirect:User.htm");
I am getting the following error
java.lang.IllegalStateException: Neither BindingResult nor plain target object for
bean name 'User' available as request attribute
I searched but i cannot find a proper explanation for modelandview..

Answer 1

When using the modelAttribute make user that:1. Your method parameter user is annotated with #ModelAttribute("user")2. A method parameter of type BindingResult is declared.
Also, the annotation parameter value is case sensitive, and should exactly match the value of the modelAttribute you declared in userForm.jsp.