Question

I’m trying to create a form using Spring @MVC 3.0. This form is supposed to let the user update the flavor of a soup, but I’m running into some issues. Here are my relevant model classes (assume all the getters and setters are there):

public class Soup {
   String name, flavor, mainIngredient;
   public String toString() 
   {
      return "name: " + this.name + ", flavor: " 
             + this.flavor + ", main: " + this.mainIngredient;
   }
}

public class SmallMeal {
    List<Soup> soups;
}

public class Menu {
    String id;
    SmallMeal smallMeals;
}

This part of the application allows the user to edit the soups. Here’s the controller:

public class MenuController {

  @RequestMapping(value="/soupForm", method = RequestMethod.GET)
  public String updateSoups(
     @PathVariable("menuId") String menuId,
     ModelMap model) 
  {
     Menu menu = // ... looked up with a DAO.
     if (menu != null)
     {
        model.addAttribute("menu", menu);
        for (Soup s : menu.getSmallMeal().getSoups())
        {
           System.out.println("soup: " + s.toString());
        }
     }
     return "soupEditor";
  }

  @RequestMapping(value="/soupForm", method = RequestMethod.POST)
  public String updateSoups(
     @ModelAttribute("menu") Menu menu,
     BindingResult result, SessionStatus status)
  {
     for (Soup s : menu.getSmallMeal().getSoups())
     {
        System.out.println("soup: " + s.toString());
     }
     return "redirect:soupUpdated";
  }

}

And here’s the soupForm JSP:

<form:form modelAttribute="menu">
  <c:forEach var="soup" varStatus="stat" items="${menu.smallMeal.soups}">
     <label>${soup.name} flavor</label>
     <form:input path="smallMeal.soups[${stat.index}].flavor" />
  </c:forEach>
</form:form>

Now, when I first request the page, I get an output similar to this:

name: tortilla, flavor: spicy, mainIngredient: tortillas
name: crab bisque, flavor: crab, mainIngredient: crab

And after I submit the form (after updating the flavor for tortilla), I would get an output similar to:

name: null, flavor: delicious, mainIngredient: null
name: null, flavor: null, mainIngredient: null

What’s going wrong? Why isn’t the rest of the data of the object being bound?

Answer 1

Turns out that the @SessionAttributes annotation was the answer.

@Controller
@SessionAttributes("menu")
public class MenuController { 

  /* ... */

}

After that was added, the data currently existing on the object persisted.