Spring MVC #ModelAttribute method - spring-mvc

Question

Question about Spring MVC #ModelAttribute methods, Setting model attributes in a controller #RequestMapping method verses setting attribute individually with #ModelAttribute methods, which one is considered better and is more used?
From design point of view which approach is considered better from the following:
Approach 1
#ModelAttribute("message")
public String addMessage(#PathVariable("userName") String userName, ModelMap model) {
LOGGER.info("addMessage - " + userName);
return "Spring 3 MVC Hello World - " + userName;
}
#RequestMapping(value="/welcome/{userName}", method = RequestMethod.GET)
public String printWelcome(#PathVariable("userName") String userName, ModelMap model) {
LOGGER.info("printWelcome - " + userName);
return "hello";
}
Approach 2
#RequestMapping(value="/welcome/{userName}", method = RequestMethod.GET)
public String printWelcome(#PathVariable("userName") String userName, ModelMap model) {
LOGGER.info("printWelcome - " + userName);
model.addAttribute("message", "Spring 3 MVC Hello World - " + userName);
return "hello";
}

Answer 1

The #ModelAttribute annotation serves two purposes depending on how it is used:
At Method level
Use #ModelAttribute at the method level to provide reference data for the model. #ModelAttribute annotated methods are executed before the chosen #RequestMapping annotated handler method. They effectively pre-populate the implicit model with specific attributes, often loaded from a database. Such an attribute can then already be accessed through #ModelAttribute annotated handler method parameters in the chosen handler method, potentially with binding and validation applied to it.
In other words; a method annotated with #ModelAttribute will populate the specified “key” in the model. This happens BEFORE the #RequestMapping
At Method Parameter level
At Method Parameter level
When you place #ModelAttribute on a method parameter, #ModelAttribute maps a model attribute to the specific, annotated method parameter. This is how the controller gets a reference to the object holding the data entered in the form.
Examples
Method Level
#Controller
public class MyController {
#ModelAttribute("productsList")
public Collection<Product> populateProducts() {
return this.productsService.getProducts();
}
}
So, in the above example, “productsList” in the Model is populated before the the #RequestMapping is performed.
Method parameter level
#Controller
public class MyController {
#RequestMapping(method = RequestMethod.POST)
public String processSubmit(#ModelAttribute("product") Product myProduct, BindingResult result, SessionStatus status) {
new ProductValidator().validate(myProduct, result);
if (result.hasErrors()) {
return "productForm";
}
else {
this.productsService.saveProduct(myProduct);
status.setComplete();
return "productSaved";
}
}
}
Look here for detailed information with examples.

Answer 2

One is not better then the other. They both serve another purpose.
Method: If you need the model for a particular controller to be always populated with certain attributes the method level #ModelAttribute makes more sense.
Parameter: Use it on a parameter when you want to bind data from the request and add it to the model implicitly.
To answer your question on the better approach
I would say approach 2 is better since the data is specific to that handler.