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RESTX i18n support

RESTX has some support for i18n (internationalization), aimed to be used in a SPA (single page application).

enabling i18n support

You need to add a dependency on restx-i18n to enable RESTX support for i18n.

You can do that with the shell:

restx deps add io.restx:restx-i18n:0.34.1

RESTX Messages

RESTX i18n relies on a mechanism used to access internationalized messages accessed through a Messages interface.

A Messages is something very similar to a standard Java ResourceBundle (default implementation actually uses one underneath), so most of the documentation you can find for standard Java ResourceBundle, except that the files are encoded in UTF-8 (as everything in RESTX).

accessing Messages in RESTX app

When i18n is enabled your application benefits from a default Messages component that can be injected in any of your components.


public class MyComponent {
    public MyComponent(Messages messages) {
        this.messages = messages;

If you intend to use several Messages instances, name it when you ask for injection:

public class MyComponent {
    public MyComponent(@Named("messages") Messages messages) {
        this.messages = messages;

This instance loads its messages from a labels resource bundle at the root of your application classpath. So all you need to do to provide messages in this instance is to create a file in your src/main/resources directory (if using default project layout). Then you can provide each locale using the _XX suffix as with standard resource bundles.

For instance:


accessing Messages from a REST client

by default the i18n module exposes the default Messages instance through a REST API.

This REST API is intented to be used by a SPA, and supports only basic operations.

It relies on the request locale to supply the messages. This means that it will provide the translations based on the standard HTTP Accept-Language header, and if not present it will use the default locale of the server.

You can access the default labels on /i18n/labels.json where you will get the key / messages in json format.

You can also access them on /i18n/labels.js where you will get them in javascript so that you can load them using a <script> tag in your SPA. This is interesting because by default <script> loading is blocking, so you don’t have to deal with an async interpolation of you keys / labels in your application.

The script served on this endpoint is similar to what is produced in json, except that it is decorated with a template to deal with it in javascript.

The default template is:

// RESTX Labels - customize this with restx.i18n.labelsJsTemplate named String
window.labels = {LABELS};

As you can see it simply assigns the labels in a global variable named labels.

You can easily customize that by providing your own template as a named string in your RESTX app.

For instance in a module:

@Provides @Named("restx.i18n.labelsJsTemplate")
public String labelsJsTemplte() {
    return "window.mylabels= {LABELS};";

Message parameter interpolation

Another difference with standard Java resource bundle is that the Messages API supports a message parameter interpolation using mustache format rather than the standard Java format. This makes the message templates much easier to use on the client side, mustache having a very wide support, including very good support in Javascript.

Here is an example of use:

messages.getMessage("some.msg.key", MessageParams.of("who", "World"), Locale.ENGLISH)

which with following

some.msg.key=Hello {{who}}!

will produce Hello World!