§I18N API Migration

There are a number of changes to the I18N API to make working with messages and languages easier to use, particularly with forms and templates.

§Java API

§Refactored Messages API to interfaces

The play.i18n package has changed to make access to Messages easier. These changes should be transparent to the user, but are provided here for teams extending the I18N API.

Messages is now an interface, and there is a MessagesImpl class that implements that interface.

§Deprecated / Removed Methods

The static deprecated methods in play.i18n.Messages have been removed in 2.6.x, as there are equivalent methods on the MessagesApi instance.

§Scala API

§Removed Implicit Default Lang

The Lang singleton object has a defaultLang that points to the JVM default Locale. Pre 2.6.x, defaultLang was an implicit value, with the result that it could be used in implicit scope resolution if no Lang was found in local scope. This setting was too general and resulted in bugs where defaultLang was being used instead of a request’s locale, if the request was not declared as implicit.

As a result, the implicit has been removed, and so what was:

object Lang {
  implicit lazy val defaultLang: Lang = Lang(java.util.Locale.getDefault)

is now:

object Lang {
  lazy val defaultLang: Lang = Lang(java.util.Locale.getDefault)

Any code that was relying on this implicit should use Lang.defaultLang explicitly.

§Refactored Messages API to traits

The play.api.i18n package has changed to make access to Messages instances easier and reduce the number of implicits in play. These changes should be transparent to the user, but are provided here for teams extending the I18N API.

Messages is now a trait (rather than a case class). The case class is now MessagesImpl, which implements Messages.

§I18nSupport Implicit Conversion

If you are upgrading directly from Play 2.5 to Play 2.6, you should know that I18nSupport support has changed in 2.6.x. In 2.5.x, it was possible through a series of implicits to use a “language default” Messages instance if the request was not declared to be in implicit scope:

  def listWidgets = Action {
    val lang = implicitly[Lang] // Uses Lang.defaultLang
    val messages = implicitly[Messages] // Uses I18nSupport.lang2messages(Lang.defaultLang)
    // implicit parameter messages: Messages in requiresMessages template, but no request!
    val content = views.html.requiresMessages(form)

The I18nSupport implicit conversion now requires an implicit request or request header in scope in order to correctly determine the preferred locale and language for the request.

This means if you have the following:

def index = Action {


You need to change it to:

def index = Action { implicit request =>


This will allow i18n support to see the request’s locale and provide error messages and validation alerts in the user’s language.

§Smoother I18nSupport

Using a form inside a controller is a smoother experience in 2.6.x. ControllerComponents contains a MessagesApi instance, which is exposed by AbstractController. This means that the I18nSupport trait does not require an explicit val messagesApi: MessagesApi declaration, as it did in Play 2.5.x.

class FormController @Inject()(components: ControllerComponents)
  extends AbstractController(components) with I18nSupport {


  val userForm = Form(
      "name" -> text.verifying(nonEmpty),
      "age" -> number.verifying(min(0), max(100))

  def index = Action { implicit request =>
    // use request2messages implicit conversion method

  def showMessage = Action { request =>
    // uses type enrichment

  def userPost = Action { implicit request =>
      formWithErrors => {
      user => {
        Redirect(routes.FormController.index()).flashing("success" -> s"User is ${user}!")

Note there is now also type enrichment in I18nSupport which adds request.messages and request.lang. This can be added either by extending from I18nSupport, or by import I18nSupport._. The import version does not contain the request2messages implicit conversion.

§Integrated Messages with MessagesProvider

A new MessagesProvider trait is available, which exposes a Messages instance.

trait MessagesProvider {
  def messages: Messages

MessagesImpl implements Messages and MessagesProvider, and returns itself by default.

All the template helpers now take MessagesProvider as an implicit parameter, rather than a straight Messages object, i.e. inputText.scala.html takes the following:

@(field:, args: (Symbol,Any)*)(implicit handler: FieldConstructor, messagesProvider: play.api.i18n.MessagesProvider)

The benefit to using a MessagesProvider is that otherwise, if you used implicit Messages, you would have to introduce implicit conversions from other types like Request in places where those implicits could be confusing.

§MessagesRequest and MessagesAbstractController

To assist, there’s MessagesRequest, which is a WrappedRequest that implements MessagesProvider and provides the preferred language.

You can access a MessagesRequest by using a MessagesActionBuilder:

class MyController @Inject()( messagesAction: MessagesActionBuilder, cc: ControllerComponents ) extends AbstractController(cc) { def index = messagesAction { implicit request: MessagesRequest[AnyContent] => Ok(views.html.formTemplate(form)) // twirl template with form builders } }

Or you can use MessagesAbstractController, which swaps out the default Action that provides MessagesRequest instead of Request in the block:

class MyController @Inject() ( mcc: MessagesControllerComponents ) extends MessagesAbstractController(mcc) { def index = Action { implicit request: MessagesRequest[AnyContent] => Ok(s"The messages are ${request.messages}") } }

Here’s a complete example using a form with a CSRF action (assuming that you have CSRF filter disabled):

class MyController @Inject() ( addToken: CSRFAddToken, checkToken: CSRFCheck, mcc: MessagesControllerComponents ) extends MessagesAbstractController(mcc) { import import val userForm = Form( mapping( "name" -> text, "age" -> number )(UserData.apply)(UserData.unapply) ) def index = addToken { Action { implicit request => Ok(views.html.formpage(userForm)) } } def userPost = checkToken { Action { implicit request => userForm.bindFromRequest.fold( formWithErrors => {"unsuccessful user submission") BadRequest(views.html.formpage(formWithErrors)) }, user => {"successful user submission ${user}") Redirect(routes.MyController.index()).flashing("success" -> s"User is ${user}!") } ) } } }

Because MessagesRequest is a MessagesProvider, you only have to define the request as implicit and it will carry through to the template. This is especially useful when CSRF checks are involved. The formpage.scala.html page is as follow:

@(userForm: Form[UserData])(implicit request: MessagesRequestHeader) @helper.form(action = routes.MyController.userPost()) { @views.html.helper.CSRF.formField @helper.inputText(userForm("name")) @helper.inputText(userForm("age")) <input type="submit" value="SUBMIT"/> }

Note that because the body of the MessageRequest is not relevant to the template, we can use MessagesRequestHeader here instead of MessageRequest[_].

Please see passing messages to form helpers for more details.

§DefaultMessagesApi component

The default implementation of MessagesApi is DefaultMessagesApi. DefaultMessagesApi used to take Configuration and Environment directly, which made it awkward to deal with in forms. For unit testing purposes, DefaultMessagesApi can be instantiated without arguments, and will take a raw map.

import import import play.api.i18n._ val messagesApi = new DefaultMessagesApi( Map("en" -> Map("error.min" -> "minimum!") ) ) implicit val request = { play.api.test.FakeRequest("POST", "/") .withFormUrlEncodedBody("name" -> "Play", "age" -> "-1") } implicit val messages = messagesApi.preferred(request) def errorFunc(badForm: Form[UserData]) = { BadRequest(badForm.errorsAsJson) } def successFunc(userData: UserData) = { Redirect("/").flashing("success" -> "success form!") } val result = Future.successful(form.bindFromRequest().fold(errorFunc, successFunc)) Json.parse(contentAsString(result)) must beEqualTo(Json.obj("age" -> Json.arr("minimum!")))

For functional tests that involve configuration, the best option is to use WithApplication and pull in an injected MessagesApi:

import play.api.test.{ PlaySpecification, WithApplication } import play.api.i18n._ class MessagesSpec extends PlaySpecification { sequential implicit val lang = Lang("en-US") "Messages" should { "provide default messages" in new WithApplication(_.requireExplicitBindings()) { val messagesApi = app.injector.instanceOf[MessagesApi] val javaMessagesApi = app.injector.instanceOf[play.i18n.MessagesApi] val msg = messagesApi("") val javaMsg = javaMessagesApi.get(new play.i18n.Lang(lang), "") msg must ===("Email") msg must ===(javaMsg) } "permit default override" in new WithApplication(_.requireExplicitBindings()) { val messagesApi = app.injector.instanceOf[MessagesApi] val msg = messagesApi("constraint.required") msg must ===("Required!") } } }

If you need to customize the configuration, it’s better to add configuration values into the GuiceApplicationBuilder rather than use the DefaultMessagesApiProvider directly.

§Deprecated Methods

play.api.i18n.Messages.Implicits.applicationMessagesApi and play.api.i18n.Messages.Implicits.applicationMessages have been deprecated, because they rely on an implicit Application instance.

The play.api.mvc.Controller.request2lang method has been deprecated, because it was using a global Application under the hood.

The play.api.i18n.I18nSupport.request2Messages implicit conversion method has been moved to I18NSupportLowPriorityImplicits.request2Messages, and deprecated in favor of request.messages type enrichment, which is clearer overall.

The I18NSupportLowPriorityImplicits.lang2Messages implicit conversion has been moved out to LangImplicits.lang2Messages, because of confusion when both implicit Request and a Lang were in scope. Please extend the play.api.i18n.LangImplicits trait specifically if you want to create a Messages from an implicit Lang.

Next: WS Migration

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