Model
You can use the @ModelAttribute
annotation:
-
On a method argument in
@RequestMapping
methods to create or access an Object from the model and to bind it to the request through aWebDataBinder
. -
As a method-level annotation in
@Controller
or@ControllerAdvice
classes, helping to initialize the model prior to any@RequestMapping
method invocation. -
On a
@RequestMapping
method to mark its return value as a model attribute.
This section discusses @ModelAttribute
methods, or the second item from the preceding list.
A controller can have any number of @ModelAttribute
methods. All such methods are
invoked before @RequestMapping
methods in the same controller. A @ModelAttribute
method can also be shared across controllers through @ControllerAdvice
. See the section on
Controller Advice for more details.
@ModelAttribute
methods have flexible method signatures. They support many of the same
arguments as @RequestMapping
methods (except for @ModelAttribute
itself and anything
related to the request body).
The following example uses a @ModelAttribute
method:
-
Java
-
Kotlin
@ModelAttribute
public void populateModel(@RequestParam String number, Model model) {
model.addAttribute(accountRepository.findAccount(number));
// add more ...
}
@ModelAttribute
fun populateModel(@RequestParam number: String, model: Model) {
model.addAttribute(accountRepository.findAccount(number))
// add more ...
}
The following example adds one attribute only:
-
Java
-
Kotlin
@ModelAttribute
public Account addAccount(@RequestParam String number) {
return accountRepository.findAccount(number);
}
@ModelAttribute
fun addAccount(@RequestParam number: String): Account {
return accountRepository.findAccount(number);
}
When a name is not explicitly specified, a default name is chosen based on the type,
as explained in the javadoc for Conventions .
You can always assign an explicit name by using the overloaded addAttribute method or
through the name attribute on @ModelAttribute (for a return value).
|
Spring WebFlux, unlike Spring MVC, explicitly supports reactive types in the model
(for example, Mono<Account>
or io.reactivex.Single<Account>
). Such asynchronous model
attributes can be transparently resolved (and the model updated) to their actual values
at the time of @RequestMapping
invocation, provided a @ModelAttribute
argument is
declared without a wrapper, as the following example shows:
-
Java
-
Kotlin
@ModelAttribute
public void addAccount(@RequestParam String number) {
Mono<Account> accountMono = accountRepository.findAccount(number);
model.addAttribute("account", accountMono);
}
@PostMapping("/accounts")
public String handle(@ModelAttribute Account account, BindingResult errors) {
// ...
}
import org.springframework.ui.set
@ModelAttribute
fun addAccount(@RequestParam number: String) {
val accountMono: Mono<Account> = accountRepository.findAccount(number)
model["account"] = accountMono
}
@PostMapping("/accounts")
fun handle(@ModelAttribute account: Account, errors: BindingResult): String {
// ...
}
In addition, any model attributes that have a reactive type wrapper are resolved to their actual values (and the model updated) just prior to view rendering.
You can also use @ModelAttribute
as a method-level annotation on @RequestMapping
methods, in which case the return value of the @RequestMapping
method is interpreted as a
model attribute. This is typically not required, as it is the default behavior in HTML
controllers, unless the return value is a String
that would otherwise be interpreted
as a view name. @ModelAttribute
can also help to customize the model attribute name,
as the following example shows:
-
Java
-
Kotlin
@GetMapping("/accounts/{id}")
@ModelAttribute("myAccount")
public Account handle() {
// ...
return account;
}
@GetMapping("/accounts/{id}")
@ModelAttribute("myAccount")
fun handle(): Account {
// ...
return account
}