Java ResourceBundle

By Arvind Rai, July 18, 2019
Core Java
ResourceBundle contains locale-specific objects by loading locale-specific resource. ResourceBundle loads the resource according to current user' locale. This helps the developer to write program independent of user' locale. Using ResourceBundle, we can optimize our application in different locales easily, handle multiple locales and application can be modified for more locales later. To use ResourceBundle, our all resources name should contain a base name as prefix and locale as suffix.
ResourceBundle has two known subclasses i.e. ListResourceBundle and PropertyResourceBundle. The ListResourceBundle works with resource bundle as Java classes and PropertyResourceBundle works with property files. Both approach has to follow same naming convention i.e. the combination of base name and locale. To get a ResourceBundle instance, we need to call ResourceBundle.getBundle method and pass resource base name and locale. To fetch the value for a key from resources, we need to call getObject, getString and getStringArray methods of ResourceBundle on the instance of ResourceBundle and pass key as string.
Contents

Naming of Resource Bundles

Resource bundles can be a property file or Java class. The resource bundle names are created by combining a base name and locale. Find the sample examples.
1. Property File: Suppose myapp is property file base name then we will create resource bundle files as following. 
myapp.properties 
myapp_en_CA.properties
myapp_de_DE.properties
myapp_fr_FR.properties
The resource bundle property file will be loaded according to user's current Locale.
a. For default Locale the resource file name will be myapp.properties.
b. For Locale("en", "CA") the resource file name will be myapp_en_CA.properties.
c. For Locale("de", "DE") the resource file name will be myapp_de_DE.properties.
d. For Locale("fr", "FR") the resource file name will be myapp_fr_FR.properties

2. Java Class: Resource bundle classes are created as subclasses of ListResourceBundle. Suppose MyApp is base class name, we will create resource bundle classes as following. 
MyApp.class 
MyApp_en_CA.class
MyApp_de_DE.class
MyApp_fr_FR.class
The resource bundle classes will be loaded according to user's current Locale.
a. For default Locale the resource class name will be MyApp.class.
b. For Locale("en", "CA") the resource class name will be MyApp_en_CA.class.
c. For Locale("de", "DE") the resource class name will be MyApp_de_DE.class.
d. For Locale("fr", "FR") the resource class name will be MyApp_fr_FR.class

Property Files as ResourceBundle

We will create an example of ResourceBundle using property file with locales en_CA, de_DE, fr_FR and default locale.
1. Create resource bundle property files
myapp.properties 
user.name= Enter user name
user.pwd= Enter password
user.submit= Submit
myapp_en_CA.properties 
user.name= Enter user name (CA)
user.pwd= Enter password (CA)
user.submit= Submit (CA)
myapp_de_DE.properties 
user.name= Benutzernamen eingeben
user.pwd= Passwort eingeben
user.submit= einreichen
myapp_fr_FR.properties 
user.name= Saisissez votre nom d'utilisateur
user.pwd= Entrer le mot de passe
user.submit= Soumettre

2. Create ResourceBundle and fetch value
To create ResourceBundle, we need to call ResourceBundle.getBundle method and pass resource base name and locale. In our example resource file base name is myapp. Find the code. 
ResourceBundle rs = 
    ResourceBundle.getBundle("com.concretepage.lsbundles.MyDataBundle", new Locale("de", "DE"));
To fetch the value for a key from resource, we can call getObject, getString and getStringArray methods of ResourceBundle and pass key as string. 
String username = rs.getString("user.name");
String password = rs.getString("user.pwd");
String submit = rs.getString("user.submit");
Find the example.
MyApplication.java 
package com.concretepage;
import java.util.Locale;
import java.util.ResourceBundle;
public class MyApplication {
  public static void main(String[] args) {
        System.out.println("---For Locale de_DE---");
	ResourceBundle rs = ResourceBundle.getBundle("myapp", new Locale("de", "DE"));
	displayPropDetails(rs);

	System.out.println("---For Locale en_CA---");
	rs = ResourceBundle.getBundle("myapp", new Locale("en", "CA"));
	displayPropDetails(rs);

	System.out.println("---For Locale fr_FR---");
	rs = ResourceBundle.getBundle("myapp", new Locale("fr", "FR"));
	displayPropDetails(rs);
	
	System.out.println("---For Default Locale---");
	rs = ResourceBundle.getBundle("myapp", Locale.getDefault());
	displayPropDetails(rs);	
  }

  private static void displayPropDetails(ResourceBundle rs) {
	String username = rs.getString("user.name");
	String password = rs.getString("user.pwd");
	String submit = rs.getString("user.submit");	

	System.out.println(username + " | " + password + " | " + submit);
  }
}
Output 
---For Locale de_DE---
Benutzernamen eingeben | Passwort eingeben | einreichen
---For Locale en_CA---
Enter user name (CA) | Enter password (CA) | Submit (CA)
---For Locale fr_FR---
Saisissez votre nom d'utilisateur | Entrer le mot de passe | Soumettre
---For Default Locale---
Enter user name | Enter password | Submit
Using getKeys()
: We can iterate all the keys using getKeys() method of ResourceBundle and fetch values using the keys. 
ResourceBundle rs = ResourceBundle.getBundle("myapp", new Locale("de", "DE"));
Enumeration<String> en = rs.getKeys();
while(en.hasMoreElements()){
    String key= en.nextElement();
    System.out.println("key:"+ key +", Values:"+rs.getString(key));
}

Classes as ResourceBundle

To use classes as resource bundle we need to create subclasses of Java ListResourceBundle. The ListResourceBundle is an abstract class of ResourceBundle that manages resources for a locale. Resources are created as Java classes. To create resource classes, we need to create subclasses of ListResourceBundle for every required locale and override its getContents() method.
We will create an example of ResourceBundle using Java classes with locales en_CA, de_DE, fr_FR and default locale.
1. Create resource bundle classes
MyApp.java 
package com.concretepage.resourcebundle;
import java.util.Arrays;
import java.util.ListResourceBundle;
import com.concretepage.StateHead;

public class MyApp extends ListResourceBundle {
  @Override
  protected Object[][] getContents() {
	return contents;
  }
  private Object[][] contents = {
      { "location", "United States" },
      { "literacy", Double.valueOf(99.20) },
      { "famousCities", Arrays.asList("New York", "Chicago", "Charleston") }, 
      { "stateHead", new StateHead("Donald Trump", 73) }   
  };
}
MyApp_en_CA.java 
package com.concretepage.resourcebundle;
import java.util.Arrays;
import java.util.ListResourceBundle;
import com.concretepage.StateHead;

public class MyApp_en_CA extends ListResourceBundle {
  @Override
  protected Object[][] getContents() {
	return contents;
  }
  private Object[][] contents = {
      { "location", "Canada" },
      { "literacy", Double.valueOf(99.00) },
      { "famousCities", Arrays.asList("Toronto", "Vancouver", "Montreal") }, 
      { "stateHead", new StateHead("Justin Trudeau", 47) }   
  };
}
MyApp_de_DE.java 
package com.concretepage.resourcebundle;
import java.util.Arrays;
import java.util.ListResourceBundle;
import com.concretepage.StateHead;

public class MyApp_de_DE extends ListResourceBundle {
  @Override
  protected Object[][] getContents() {
	return contents;
  }
  private Object[][] contents = {
      { "location", "Germany" },
      { "literacy", Double.valueOf(98.40) },
      { "famousCities", Arrays.asList("Berlin", "Munich", "Frankfurt") }, 
      { "stateHead", new StateHead("Frank-Walter", 63) }   
  };
}
MyApp_fr_FR.java 
package com.concretepage.resourcebundle;
import java.util.Arrays;
import java.util.ListResourceBundle;
import com.concretepage.StateHead;

public class MyApp_fr_FR extends ListResourceBundle {
  @Override
  protected Object[][] getContents() {
	return contents;
  }
  private Object[][] contents = {
      { "location", "France" },
      { "literacy", Double.valueOf(99.50) },
      { "famousCities", Arrays.asList("Paris", "Lyon", "Nice") }, 
      { "stateHead", new StateHead("Emmanuel Macron", 41) }   
  };
}
StateHead.java 
package com.concretepage;
public class StateHead {
  private String name;
  private int age;
  public StateHead(String name, int age) {
	this.name = name;
	this.age = age;
  }
  public String getName() {
	return name;
  }
  public int getAge() {
	return age;
  }
}

2. Create ResourceBundle and fetch value
To create ResourceBundle, we need to call ResourceBundle.getBundle method and pass resource base name and locale. Resource class base name is fully qualified class base name. In our example resource class base name is as following. 
com.concretepage.resourcebundle.MyApp
Now instantiate ResourceBundle. 
ResourceBundle rs = 
    ResourceBundle.getBundle("com.concretepage.lsbundles.MyDataBundle", new Locale("de", "DE"));
To fetch the value for a key from resource, we can call getObject, getString and getStringArray methods of ResourceBundle and pass key as string. When we call getObject, it returns object of Object data type and we can typecast it in our required data type. 
String location = rs.getString("location");
Double literacy = (Double)rs.getObject("literacy");
List<?> famousCities = (List<?>) rs.getObject("famousCities");	
StateHead stateHead = (StateHead)rs.getObject("stateHead");
Find the example.
MyApplication.java 
package com.concretepage;
import java.util.List;
import java.util.Locale;
import java.util.ResourceBundle;

public class MyApplication {
  public static void main(String[] args) {
	
    System.out.println("---For Locale de_DE---");
	ResourceBundle rs = ResourceBundle.getBundle("com.concretepage.resourcebundle.MyApp", new Locale("de", "DE"));
	displayDetails(rs);

	System.out.println("---For Locale en_CA---");
	rs = ResourceBundle.getBundle("com.concretepage.resourcebundle.MyApp", new Locale("en", "CA"));
	displayDetails(rs);

	System.out.println("---For Locale fr_FR---");
	rs = ResourceBundle.getBundle("com.concretepage.resourcebundle.MyApp", new Locale("fr", "FR"));
	displayDetails(rs);
	
	System.out.println("---For Default Locale---");
	rs = ResourceBundle.getBundle("com.concretepage.resourcebundle.MyApp", Locale.getDefault());
	displayDetails(rs);	
  }

  private static void displayDetails(ResourceBundle rs) {
	String location = rs.getString("location");
	Double literacy = (Double)rs.getObject("literacy");
	List<?> famousCities = (List<?>) rs.getObject("famousCities");	
	StateHead stateHead = (StateHead)rs.getObject("stateHead");
	
	System.out.println(location);
	System.out.println(literacy);	
	famousCities.forEach(s -> System.out.print(s + " "));
	System.out.println("\n" + stateHead.getName() + "-" + stateHead.getAge());
  }
}
Output 
---For Locale de_DE---
Germany
98.4
Berlin Munich Frankfurt 
Frank-Walter-63
---For Locale en_CA---
Canada
99.0
Toronto Vancouver Montreal 
Justin Trudeau-47
---For Locale fr_FR---
France
99.5
Paris Lyon Nice 
Emmanuel Macron-41
---For Default Locale---
United States
99.2
New York Chicago Charleston 
Donald Trump-73

References

Class ResourceBundle
Using a ListResourceBundle

Download Source Code

ResourceBundle with Property Files
ResourceBundle with Classes
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POSTED BY
ARVIND RAI
ARVIND RAI
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