Resource bundles and i18n

Seesaw has built-in support for internationalization (i18n) and generally off-loading an apps text and appearance to a ResourceBundle. It relies on Meikel Brandmeyer's j18n library.

Here's and simple example usage along with English and German translations.

Basics

The basic idea is to create one or more properties files called resource bundles. A base file used for the default locale, and then any number of locale-specific specializations. The properties files must be on the classpath. Here's an example set of bundles:

src/my_app/core.properties
src/my_app/core_fr.properties
src/my_app/core_de.properties

(note that these could also go in a resources folder rather than src)

So, let's say the title of the main frame will be stored in the frame-title property:

# core.properties
frame-title=My Application

The French and German locale files would modify title appropriately. Then in src/my-app/core.clj:

(ns my-app.core
  (:use seesaw.core))

(defn -main [& args]
  (-> (frame :title ::frame-title) pack! show!))

That's it! Note that the value of the frame's :title option is given as a namespace-qualified keyword. It could also have been written more explicitly as :my-app.core/frame-title. Seesaw passes the keyword to j18n which uses Java's ResourceBundle support to lookup the keyword in the properties file.

Other Properties

Resource properties can be used in any text options in Seesaw. e.g., :title, :text, :name, :tip, etc. Furthermore, fonts, colors, and icons can also be specified. For example:

my-button.font=ARIAL-BOLD-20
my-button.icon=path/or/url/to/icon.png
my-button.foreground=red

The :resource Prefix Option

Several widgets (buttons, labels, menu items, etc) and actions also support the :resource option. It is given as a prefix for a set of properties in the resource bundle to be applied to the target object. For example, create a button like this:

(button :resource :my-app.core/my-button)

and the my-button.text, my-button.foreground, etc properties from src/my_app/core.properties (or locale-specific file) will be applied to the button.

Changing the Default Locale

To change the default locale for testing, set the user.language system property. With Leiningen, you can do it like this:

$ export JVM_OPTS=-Duser.language=de
$ lein run

(this sets the locale to German).