Question

In this tutorial we show how to work with a ResourceBundle in Java.

A resource bundle is a Java properties file that contains locale-specific data. It is a way of internationalizing Java applications by making the code locale-independent.

Hard-coding locale-specific data is not the way to go. Values such as messages or labels should be placed in a separate file. This way we can handle multiple locales without having to write different code for each locale. It is also convenient for translators because they only work with translatable text and do not look at the programming code.

Resouce bundles are organized into families with a common base name. For instance, if we have a words base name, words_sk matches the locale for the Slovak language. The default resource bundle is used if a specific locale is not supported.

Resource bundles also support dialects; for example words_es_AR is used for Spanish language used in Argentina and words_es_BO in Bolivia.

ResourceBundle is an abstract class that has two subclasses: PropertyResourceBundle and ListResourceBundle . PropertyResourceBundle loads the data from a properties file. A properties file is a plain-text file that contains translatable text. Properties files are not part of the Java source code, and they can contain only String values. ListResourceBundle manages resources with a convenient list; it gets the data from a class file. We can store any locale-specific object in a ListResourceBundle .

To get the appropriate ResourceBundle , we invoke the ResourceBundle.getBundle() method. It is a factory method that looks for a ListResourceBundle , and if it does not find any, it looks for a PropertyResourceBundle . A MissingResourceException is thrown if no resource bundle is found.

Using PropertyResourceBundle

In the first application, we create a simple Java application that uses three resource bundles: default English, German, and Slovak.

Figure: NetBeans project structure

We create three properties files and place them into the resources directory.

words.properties

w1 = Earth
w2 = ocean

This is the default properties file; it is typically in English language. We have two words inside the file.

words_de.properties

w1 = Erde
w2 = ozean

The words_de.properties file contains words in German language.

words_sk.properties

w1 = Zem
w2 = oceán

The words_de.properties file contains words in Slovak language.

ResourceBundleEx.java

package com.zetcode;

import java.util.Locale;
import java.util.ResourceBundle;

public class ResourceBundleEx {

  static public void main(String[] args) {

    Locale[] locales = {
      Locale.GERMAN,
      new Locale("sk", "SK"),
      Locale.ENGLISH
    };

    System.out.println("w1:");

    for (Locale locale : locales) {

      getWord(locale, "w1");
    }

    System.out.println("w2:");

    for (Locale locale : locales) {

      getWord(locale, "w2");
    }
  }

  static void getWord(Locale curLoc, String key) {

    ResourceBundle words
        = ResourceBundle.getBundle("resources/words", curLoc);

    String value = words.getString(key);

    System.out.printf("Locale: %s, Value: %s %n", curLoc.toString(), value);

  }
}

In the code example, we print all the words used in three resource bundles.

Locale[] locales = {
  Locale.GERMAN,
  new Locale("sk", "SK"),
  Locale.ENGLISH
};

We have three locales in the example: German, Slovak, and English.

for (Locale locale : locales) {
  
  getWord(locale, "w1");
}

We go through the locales and print the words marked with the w1 key.

ResourceBundle words
    = ResourceBundle.getBundle("resources/words", curLoc);

With the ResourceBundle.getBundle() method, we get the bundle for the currently used locale. Since we have not created a ListResourceBundle , the method uses a PropertyResourceBundle , whis loads the data from a properties file.

String value = words.getString(key);

System.out.printf("Locale: %s, Value: %s %n", curLoc.toString(), value);

We get the value and print the locale name, the key, and the value.

w1:
Locale: de, Value: Erde 
Locale: sk_SK, Value: Zem 
Locale: en, Value: Earth 
w2:
Locale: de, Value: ozean 
Locale: sk_SK, Value: oceán 
Locale: en, Value: ocean 

This is the output of the example.

Using ListResourceBundle

In the following application, we use the ListResourceBundle .

Figure: NetBeans project structure II

We create locale resources for Slovak and Czech languages.

MyResources_sk.java

package com.zetcode.myres;

import java.util.ListResourceBundle;

public class MyResources_sk extends ListResourceBundle {

  @Override
  protected Object[][] getContents() {
    
    return resources;
  }

  private final Object[][] resources = {
    
      { "Capital", "Bratislava" },     
      { "Area", 49035 },
      { "Currency", "EUR" },
  };
}

Here we have an implementation of the ListResourceBundle for the Slovak language. We have to override the getContents() method. The method returns an array of key/value pairs.

MyResources_cs_CZ.java

package com.zetcode.myres;

import java.util.ListResourceBundle;

public class MyResources_cs_CZ extends ListResourceBundle {

  @Override
  protected Object[][] getContents() {
  
    return resources;
  }

  private final Object[][] resources = {
  
      { "Capital", "Praha" },     
      { "Area", 78866 },
      { "Currency", "CZK" },
  };
}

This is the implementation for the Czech language.

ResourceBundleEx2.java

package com.zetcode;

import java.util.Locale;
import java.util.ResourceBundle;

public class ResourceBundleEx2 {

  public static void main(String[] args) {
    
    Locale sk_loc = new Locale("sk", "SK"); 
    ResourceBundle bundle = 
      ResourceBundle.getBundle("com.zetcode.myres.MyResources", sk_loc);

    System.out.println("Capital: " + bundle.getObject("Capital"));
    System.out.println("Area: " + bundle.getObject("Area"));
    System.out.println("Currency: " + bundle.getObject("Currency"));
    
    System.out.println();
    
    Locale cz_loc = new Locale("cs", "CZ"); 
    ResourceBundle bundle2 = 
      ResourceBundle.getBundle("com.zetcode.myres.MyResources", cz_loc);

    System.out.println("Capital: " + bundle2.getObject("Capital"));
    System.out.println("Area: " + bundle2.getObject("Area"));
    System.out.println("Currency: " + bundle2.getObject("Currency"));    
  }
}

The example prints some geographical data for Slovakia and Czech Republic.

Locale sk_loc = new Locale("sk", "SK"); 
ResourceBundle bundle = 
  ResourceBundle.getBundle("com.zetcode.myres.MyResources", sk_loc);

With the ResourceBundle.getBundle() method, we create a resource bundle from a com.zetcode.myres.MyResources_sk.class .

Capital: Bratislava
Area: 49035
Currency: EUR
Capital: Praha
Area: 78866
Currency: CZK

This is the output of the example.

Swing application

In the third example, we create a simple GUI application using Java Swing. The example enables to dynamically change the language of the UI. The example uses the ListResourceBundle class. For those who are not familiar with Swing, there is a Java Swing tutorial on ZetCode.

The source code and the images are available at the author's Github repository .

MyResources_sk.java

package com.zetcode.myres;

import java.util.ListResourceBundle;
import javax.swing.ImageIcon;

public class MyResources_sk extends ListResourceBundle {

  @Override
  protected Object[][] getContents() {

    return resources;
  }

  private final Object[][] resources = {
    
    {"name", "Slovensko"},
    {"lang_menu", "Jazyk"},
    {"lang_sk", "Slovenčina"},
    {"lang_hu", "Maďarčina"},
    {"flag", new ImageIcon("src/resources/slovakia.png")},
    {"description", "Slovensko je vnútrozemský štát v strednej Európe."}
  };
}

These are resources for the Slovak language. We have five strings and an ImageIcon .

MyResources_hu.java

package com.zetcode.myres;

import java.util.ListResourceBundle;
import javax.swing.ImageIcon;

public class MyResources_hu extends ListResourceBundle {

  @Override
  protected Object[][] getContents() {

    return resources;
  }

  private final Object[][] resources = {
    
    {"name", "Magyarország"},
    {"lang_menu", "Nyelv"},
    {"lang_sk", "Szlovák"},
    {"lang_hu", "Magyar"},    
    {"flag", new ImageIcon("src/resources/hungary.png")},
    {"description", "Magyarország közép-európai ország "
      + "a Kárpát-medencében."}
  };
}

These are resources for the Hungarian language.

ResourceBundleEx3.java

package com.zetcode;

import java.awt.Container;
import java.awt.EventQueue;
import java.awt.event.ActionEvent;
import java.awt.event.KeyEvent;
import java.util.Locale;
import java.util.ResourceBundle;
import javax.swing.ButtonGroup;
import javax.swing.GroupLayout;
import javax.swing.Icon;
import javax.swing.JComponent;
import javax.swing.JFrame;
import javax.swing.JLabel;
import javax.swing.JMenu;
import javax.swing.JMenuBar;
import javax.swing.JRadioButtonMenuItem;
import javax.swing.LayoutStyle;

/*
 * Java ResourceBundle tutorial
 *
 * This program uses a ResourceBundle in a 
 * Java Swing application.
 *
 * Author: Jan Bodnar
 * Website: zetcode.com
 * Last modified: August 2016
 */
public class ResourceBundleEx3 extends JFrame {

  private ResourceBundle bundle;
  private JLabel flag;
  private JLabel lbl;
  private JMenu langMenu;
  private JRadioButtonMenuItem skMenuItem;
  private JRadioButtonMenuItem huMenuItem;

  public ResourceBundleEx3() {

    initUI();
  }

  private void initUI() {

    createMenuBar();

    flag = new JLabel();
    lbl = new JLabel();
    
    updateLanguage(new Locale("sk", "SK"));

    createLayout(lbl, flag);
    pack();

    setTitle(bundle.getString("name"));
    setLocationRelativeTo(null);
    setDefaultCloseOperation(EXIT_ON_CLOSE);
  }

  private void updateLanguage(Locale locale) {

    bundle = ResourceBundle.getBundle("com.zetcode.myres.MyResources", locale);
    langMenu.setText(bundle.getString("lang_menu"));
    skMenuItem.setText(bundle.getString("lang_sk"));
    huMenuItem.setText(bundle.getString("lang_hu"));
    flag.setIcon((Icon) bundle.getObject("flag"));
    lbl.setText(bundle.getString("description"));
    setTitle(bundle.getString("name"));
    pack();
  }

  private void createMenuBar() {

    JMenuBar menubar = new JMenuBar();

    langMenu = new JMenu();
    langMenu.setMnemonic(KeyEvent.VK_F);

    ButtonGroup btnGroup = new ButtonGroup();

    skMenuItem = new JRadioButtonMenuItem("Slovak", true);
    btnGroup.add(skMenuItem);

    skMenuItem.addActionListener((ActionEvent e) -> {
      updateLanguage(new Locale("sk", "SK"));
    });

    langMenu.add(skMenuItem);

    huMenuItem = new JRadioButtonMenuItem("Hungarian");
    btnGroup.add(huMenuItem);

    huMenuItem.addActionListener((ActionEvent e) -> {
      updateLanguage(new Locale("hu", "HU"));
    });

    langMenu.add(huMenuItem);

    menubar.add(langMenu);

    setJMenuBar(menubar);
  }

  private void createLayout(JComponent... arg) {

    Container pane = getContentPane();
    GroupLayout gl = new GroupLayout(pane);
    pane.setLayout(gl);

    gl.setAutoCreateContainerGaps(true);

    gl.setHorizontalGroup(gl.createParallelGroup()
        .addComponent(arg[0])
        .addComponent(arg[1])
    );

    gl.setVerticalGroup(gl.createSequentialGroup()
        .addComponent(arg[0])
        .addPreferredGap(LayoutStyle.ComponentPlacement.RELATED)
        .addComponent(arg[1])
    );
  }

  public static void main(String[] args) {

    EventQueue.invokeLater(() -> {
      ResourceBundleEx3 ex = new ResourceBundleEx3();
      ex.setVisible(true);
    });
  }
}

We have a menubar with a menu that contains two radio button menu items. Selecting a radio button menu item changes the language of the application's user interface.

private void updateLanguage(Locale locale) {

  bundle = ResourceBundle.getBundle("com.zetcode.myres.MyResources", locale);
  langMenu.setText(bundle.getString("lang_menu"));
  skMenuItem.setText(bundle.getString("lang_sk"));
  huMenuItem.setText(bundle.getString("lang_hu"));
  flag.setIcon((Icon) bundle.getObject("flag"));
  lbl.setText(bundle.getString("description"));
  setTitle(bundle.getString("name"));
  pack();
}

When we select a radio button menu item, the updateLanguage() method is called. It creates a new ResourceBundle based on the given locale and updates the menu, radio menu items, image icon, description, and frame title.

skMenuItem.addActionListener((ActionEvent e) -> {
  updateLanguage(new Locale("sk", "SK"));
});

Selecting a Slovak radio button menu item, we call the updateLanguage() method and pass a Slovak locale as a parameter.

Figure: Swing application

In this tutorial, we have covered the Java ResourceBundle . We created two console and one GUI applications. You might also want to look at the related tutorials: Java Swing tutorial , Java tutorial , or Displaying image in Java tutorial .