`@ModelAttribute`

The @ModelAttribute method parameter annotation binds request parameters onto a model object. For example:

Java
Kotlin

@PostMapping("/owners/{ownerId}/pets/{petId}/edit")
public String processSubmit(@ModelAttribute Pet pet) { (1)
	// method logic...
}

1	Bind to an instance of `Pet`.

@PostMapping("/owners/{ownerId}/pets/{petId}/edit")
fun processSubmit(@ModelAttribute pet: Pet): String { (1)
	// method logic...
}

1	Bind to an instance of `Pet`.

The Pet instance may be:

Accessed from the model where it could have been added by a @ModelAttribute method.
Accessed from the HTTP session if the model attribute was listed in the class-level @SessionAttributes annotation.
Obtained through a Converter if the model attribute name matches the name of a request value such as a path variable or a request parameter (example follows).
Instantiated through a default constructor.
Instantiated through a “primary constructor” with arguments that match to Servlet request parameters. Argument names are determined through runtime-retained parameter names in the bytecode.

As mentioned above, a Converter<String, T> may be used to obtain the model object if the model attribute name matches to the name of a request value such as a path variable or a request parameter, and there is a compatible Converter<String, T>. In the below example, the model attribute name account matches URI path variable account, and there is a registered Converter<String, Account> that perhaps retrieves it from a persistence store:

Java
Kotlin

@PutMapping("/accounts/{account}")
public String save(@ModelAttribute("account") Account account) { (1)
	// ...
}

@PutMapping("/accounts/{account}")
fun save(@ModelAttribute("account") account: Account): String { (1)
	// ...
}

By default, both constructor and property data binding are applied. However, model object design requires careful consideration, and for security reasons it is recommended either to use an object tailored specifically for web binding, or to apply constructor binding only. If property binding must still be used, then allowedFields patterns should be set to limit which properties can be set. For further details on this and example configuration, see model design.

When using constructor binding, you can customize request parameter names through an @BindParam annotation. For example:

Java
Kotlin

class Account {

    private final String firstName;

	public Account(@BindParam("first-name") String firstName) {
		this.firstName = firstName;
	}
}

class Account(@BindParam("first-name") val firstName: String)

The @BindParam may also be placed on the fields that correspond to constructor parameters. While @BindParam is supported out of the box, you can also use a different annotation by setting a DataBinder.NameResolver on DataBinder

In some cases, you may want access to a model attribute without data binding. For such cases, you can inject the Model into the controller and access it directly or, alternatively, set @ModelAttribute(binding=false), as the following example shows:

Java
Kotlin

@ModelAttribute
public AccountForm setUpForm() {
	return new AccountForm();
}

@ModelAttribute
public Account findAccount(@PathVariable String accountId) {
	return accountRepository.findOne(accountId);
}

@PostMapping("update")
public String update(AccountForm form, BindingResult result,
		@ModelAttribute(binding=false) Account account) { (1)
	// ...
}

1	Setting `@ModelAttribute(binding=false)`.

@ModelAttribute
fun setUpForm(): AccountForm {
	return AccountForm()
}

@ModelAttribute
fun findAccount(@PathVariable accountId: String): Account {
	return accountRepository.findOne(accountId)
}

@PostMapping("update")
fun update(form: AccountForm, result: BindingResult,
		   @ModelAttribute(binding = false) account: Account): String { (1)
	// ...
}

1	Setting `@ModelAt\tribute(binding=false)`.

If data binding results in errors, by default a MethodArgumentNotValidException is raised, but you can also add a BindingResult argument immediately next to the @ModelAttribute in order to handle such errors in the controller method. For example:

Java
Kotlin

@PostMapping("/owners/{ownerId}/pets/{petId}/edit")
public String processSubmit(@ModelAttribute("pet") Pet pet, BindingResult result) { (1)
	if (result.hasErrors()) {
		return "petForm";
	}
	// ...
}

1	Adding a `BindingResult` next to the `@ModelAttribute`.

@PostMapping("/owners/{ownerId}/pets/{petId}/edit")
fun processSubmit(@ModelAttribute("pet") pet: Pet, result: BindingResult): String { (1)
	if (result.hasErrors()) {
		return "petForm"
	}
	// ...
}

1	Adding a `BindingResult` next to the `@ModelAttribute`.

You can automatically apply validation after data binding by adding the jakarta.validation.Valid annotation or Spring’s @Validated annotation. See Bean Validation and Spring validation. For example:

Java
Kotlin

@PostMapping("/owners/{ownerId}/pets/{petId}/edit")
public String processSubmit(@Valid @ModelAttribute("pet") Pet pet, BindingResult result) { (1)
	if (result.hasErrors()) {
		return "petForm";
	}
	// ...
}

1	Validate the `Pet` instance.

@PostMapping("/owners/{ownerId}/pets/{petId}/edit")
fun processSubmit(@Valid @ModelAttribute("pet") pet: Pet, result: BindingResult): String { (1)
	if (result.hasErrors()) {
		return "petForm"
	}
	// ...
}

1	Validate the `Pet` instance.

If there is no BindingResult parameter after the @ModelAttribute, then MethodArgumentNotValueException is raised with the validation errors. However, if method validation applies because other parameters have @jakarta.validation.Constraint annotations, then HandlerMethodValidationException is raised instead. For more details, see the section Validation.

Using @ModelAttribute is optional. By default, any parameter that is not a simple value type as determined by BeanUtils#isSimpleProperty AND that is not resolved by any other argument resolver is treated as an implicit @ModelAttribute.

When compiling to a native image with GraalVM, the implicit @ModelAttribute support described above does not allow proper ahead-of-time inference of related data binding reflection hints. As a consequence, it is recommended to explicitly annotate method parameters with @ModelAttribute for use in a GraalVM native image.