[[webflux-ann-initbinder]]
= `DataBinder`

[.small]#xref:web/webmvc/mvc-controller/ann-initbinder.adoc[See equivalent in the Servlet stack]#

`@Controller` or `@ControllerAdvice` classes can have `@InitBinder` methods to
initialize `WebDataBinder` instances that in turn can:

* Bind request parameters to a model object.
* Convert request values from string to object property types.
* Format model object properties as strings when rendering HTML forms.

In an `@Controller`, `DataBinder` customizations apply locally within the controller,
or even to a specific model attribute referenced by name through the annotation.
In an `@ControllerAdvice` customizations can apply to all or a subset of controllers.

You can register `PropertyEditor`, `Converter`, and `Formatter` components in the
`DataBinder` for type conversion. Alternatively, you can use the
xref:web/webflux/config.adoc#webflux-config-conversion[WebFlux config] to register
`Converter` and `Formatter` components  in a globally shared `FormattingConversionService`.

--
[tabs]
======
Java::
+
[source,java,indent=0,subs="verbatim,quotes"]
----
	@Controller
	public class FormController {

		@InitBinder // <1>
		public void initBinder(WebDataBinder binder) {
			SimpleDateFormat dateFormat = new SimpleDateFormat("yyyy-MM-dd");
			dateFormat.setLenient(false);
			binder.registerCustomEditor(Date.class, new CustomDateEditor(dateFormat, false));
		}

		// ...
	}
----
<1> Using the `@InitBinder` annotation.

Kotlin::
+
[source,kotlin,indent=0,subs="verbatim,quotes"]
----
	@Controller
	class FormController {

		@InitBinder // <1>
		fun initBinder(binder: WebDataBinder) {
			val dateFormat = SimpleDateFormat("yyyy-MM-dd")
			dateFormat.isLenient = false
			binder.registerCustomEditor(Date::class.java, CustomDateEditor(dateFormat, false))
		}

		// ...
	}
----
<1> Using the `@InitBinder` annotation.
======
--

Alternatively, when using a `Formatter`-based setup through a shared
`FormattingConversionService`, you could re-use the same approach and register
controller-specific `Formatter` instances, as the following example shows:

--
[tabs]
======
Java::
+
[source,java,indent=0,subs="verbatim,quotes"]
----
	@Controller
	public class FormController {

		@InitBinder
		protected void initBinder(WebDataBinder binder) {
			binder.addCustomFormatter(new DateFormatter("yyyy-MM-dd")); <1>
		}

		// ...
	}
----
<1> Adding a custom formatter (a `DateFormatter`, in this case).

Kotlin::
+
[source,kotlin,indent=0,subs="verbatim,quotes"]
----
	@Controller
	class FormController {

		@InitBinder
		fun initBinder(binder: WebDataBinder) {
			binder.addCustomFormatter(DateFormatter("yyyy-MM-dd")) // <1>
		}

		// ...
	}
----
<1> Adding a custom formatter (a `DateFormatter`, in this case).
======
--


[[webflux-ann-initbinder-model-design]]
== Model Design
[.small]#xref:web/webmvc/mvc-controller/ann-initbinder.adoc#mvc-ann-initbinder-model-design[See equivalent in the Servlet stack]#

include::partial$web/web-data-binding-model-design.adoc[]

