How to Internationalize a RAP application

Internationalization in RAP follows the same approach as RCP. However, due to the server-side, multi-user nature of RAP, a few adaptations are necessary. In the following, you will get a step-by-step guide to internationalize the simple Hello World application created in the getting-started chapter. For a more general introduction to internationalization in RCP, see [1].

Why does RAP internationalization differ from RCP?

In RAP we have to deal with different languages for different user sessions. Indeed, the language can also change between requests within the same session. Therefore, we cannot store language related information statically in Message classes as this is done in RCP. Instead, we must use a different instance of the Message class for every language.

Move translatable strings into *.properties files

In RCP, it's quite simple to externalize strings using the Externalize Strings wizard provided by JDT. Unfortunately, this wizard is not yet prepared to externalize strings the RAP way. You can probably benefit from the assistance of the Externalize Strings wizard anyway, but only partly. Until now, you are on your own here. We will now explain how to do it from scratch.

Let's start with the preparations. You probably know the resource bundle accessor classes (usually called Messages). We also use such a class, but instead of accessing a resource bundle, we use the RAP NLS facility to access nationalized strings. We create a class Messages in the package org.eclipse.rap.helloworld with the following initial content:

  public class Messages {
  
    private static final String BUNDLE_NAME
      = "org.eclipse.rap.helloworld.messages"; //$NON-NLS-1$
    
    private Messages() {
      // prevent instantiation
    }
    
    public static Messages get() {
      Class clazz = Messages.class;
      return ( Messages )RWT.NLS.getISO8859_1Encoded( BUNDLE_NAME, clazz );
    }
  }
  

In the next step, we create an empty properties file messages.properties in the same package. This properties file follows the conventions of standard ResourceBundle properties files. For each externalized string, there has to be a key entry in the properties file.

Now we are prepared to externalize strings. Let's start with the class HelloWorldView from the hello world example. The class contains one string we'd like to externalize in order to make it translatable:

  public void createPartControl( Composite parent ) {
    Label label = new Label ( parent, SWT.NONE );
    label.setText( "Hello RAP World" );
    label.setSize( 80, 20 );
  }
  

  public void createPartControl( Composite parent ) {
    Label label = new Label ( parent, SWT.NONE );
    label.setText( Messages.get().HelloWorldView_Message );
    label.setSize( 80, 20 );
  }
  

  public class Messages {  
    ...
    public String HelloWorldView_Message;
    ...
  

  HelloWorldView_Message = Hello RAP World
  

Translate plug-in manifest

Extension definitions in the plug-in manifest file can also contain strings that are subject to internationalization. In order to get this working a few prerequisites are necessary:

• check out the plug-in org.eclipse.rap.equinox.registry from the RAP CVS
• also include the plug-in into your workspace.

Also the plug-in manifest file (plugin.xml) may contain translatable strings. Like in RCP, those stings are replaced by unique keys, prefixed with a % sign. The keys are then resolved in a plugin.properties file that resides in the root directory of the plug-in. For example, the internationalized version of the HelloWorld plug-in manifest file contains placeholders for the names of the view and the perspective.

   ...
   <extension
         point="org.eclipse.ui.views">
      <view
            id="org.eclipse.rap.helloworld.helloWorldView"
            class="org.eclipse.rap.helloworld.HelloWorldView"
            name="%helloWorldView_name">
      </view>
   </extension>
   
   <extension
         point="org.eclipse.ui.perspectives">
      <perspective
            id="org.eclipse.rap.helloworld.perspective"
            class="org.eclipse.rap.helloworld.Perspective"
            icon="icons/icon.gif"
            name="%perspective_name">
      </perspective>
   </extension>
  

  helloWorldView_name = Hello World View
  perspective_name = Hello World Perspective
  

  Bundle-Localization: plugin