Data Transfer from Controller to View

Spring MVC provides multiple mechanisms to pass data from controllers to views. Here are four primary approaches:

1. ModelAndView Approach

Handler methods returning ModelAndView objects can directly add model attributes:

@GetMapping("/model-view-example")
public ModelAndView modelViewExample() {
    String targetView = "displayPage";
    ModelAndView mav = new ModelAndView(targetView);
    
    UserProfile userProfile = new UserProfile();
    userProfile.setUsername("jdoe");
    userProfile.setPassword("secure123");
    userProfile.setRegistrationDate(LocalDate.now());
    
    mav.addObject("displayName", "John");
    mav.addObject("user", userProfile);
    return mav;
}

2. Model/Map/ModelMap Approach

Handler methods can accept Model, ModelMap, or Map parameters:

@GetMapping("/model-example")
public String modelExample(Model model) {
    UserProfile user = new UserProfile();
    user.setUsername("jsmith");
    user.setPassword("modelPass");
    user.setRegistrationDate(LocalDate.now());
    
    model.addAttribute("displayName", "Jane");
    model.addAttribute("user", user);
    return "displayPage";
}

@GetMapping("/map-example")
public String mapExample(Map<String, Object> dataMap) {
    UserProfile user = new UserProfile();
    user.setUsername("rbrown");
    user.setPassword("mapPass");
    user.setRegistrationDate(LocalDate.now());
    
    dataMap.put("displayName", "Robert");
    dataMap.put("user", user);
    return "displayPage";
}

View template access example:

<!-- displayPage.jsp -->
<div>
  Username: ${user.username}<br>
  Password: ${user.password}<br>
  Registered: ${user.registrationDate}<br>
  Display Name: ${displayName}
</div>

3. @SessionAttributes Annotation

Persist model attributes across requests using session storage:

@SessionAttributes({"user"})
@Controller
@RequestMapping("/user")
public class UserController {

    @GetMapping("/session-example")
    public String sessionExample(Model model) {
        UserProfile user = new UserProfile();
        user.setUsername("sessionUser");
        user.setPassword("sessionPass");
        model.addAttribute("user", user);
        return "displayPage";
    }
}

Accessing session attributes in views:

Session User: ${sessionScope.user.username}

4. @ModelAttribute Annotation

Bind method parametesr to model attributes or execute pre-handler methods:

Parameter Binding

@GetMapping("/attribute-param")
public String attributeParameter(@ModelAttribute("user") UserProfile user, 
                                @ModelAttribute("name") String displayName,
                                Model model) {
    user.setUsername("attributeUser");
    user.setPassword("paramPass");
    displayName = "Attribute Example";
    model.addAttribute("name", displayName);
    return "displayPage";
}

Pre-handler Methods

@ModelAttribute("preloadData")
public Map<String, Object> preloadModel() {
    UserProfile user = new UserProfile();
    user.setUsername("preloadUser");
    user.setPassword("preloadPass");
    
    Map<String, Object> modelData = new HashMap<>();
    modelData.put("displayName", "Preloaded");
    modelData.put("user", user);
    return modelData;
}

@GetMapping("/preload-example")
public String preloadExample() {
    return "displayPage";
}

Accessing preloaded data:

Preloaded Name: ${preloadData.displayName}