Read and set the locale by using the Locale object.
Create and read a Properties file.
Build a resource bundle for each locale and load a resource bundle in an application.
Localization (abbreviated as l10N because of the number of characters between the first and the last letter) is the mechanism by which an application is adapted to a specific language and region.
It's related to the concept of internationalization (abbreviated as i18n for the same reason as localization), which is about designing an application that can handle different languages and regions.
The most common things that can be customized by language and/or region are messages, dates, and numbers.
In Java, it all starts with one class, java.util.Locale.
The Locale class basically represents a language and a country although, to be precise, a locale can have the following information:
But most of the time, we just work with languages and countries.
The language part is required
The country part is optional
fr_CA
Notice the lower case in the language part
Then the underscore for separation
Notice the upper case in the country part
You can get the default locale of your machine with:
Locale locale = Locale.getDefault();
And get information like:
System.out.println("Country Code: "
+ locale.getCountry());
System.out.println("Country Name: "
+ locale.getDisplayCountry());
System.out.println("Language Code: "
+ locale.getLanguage());
System.out.println("Language Name: "
+ locale.getDisplayLanguage());
The output (notice how the actual names are localized in Spanish):
Country Code: MX
Country Name: México
Language Code: es
Language Name: español
You can also get all the locales supported by Java:
Locale [] locales = Locale.getAvailableLocales();
Arrays.stream(locales)
.forEach(System.out::println);
This would output around 160 locales in the form of language[_country], for example:
it
pt_BR
ro_RO
There are three different ways to create a Locale instance:
1. Using a constructor
There are three constructors:
Locale(String language)
Locale(String language, String country)
Locale(String language, String country, String variant)
For example:
Locale chinese = new Locale("zh");
Locale CHINA = new Locale("zh", "CN");
2. Using the forLanguageTag(String) factory method
This method expects a language code, for example:
Locale german = Locale.forLanguageTag("de");
3. Using Locale.Builder
You can set the properties you need and build the object at the end, for example:
Locale japan = new Locale.Builder()
.setRegion("JP")
.setLanguage("jp")
.build();
Passing an invalid argument to any of the above three methods will not throw an exception, it will just create an object with invalid options that will make your program behave incorrectly:
Locale badLocale = new Locale("a", "A"); // No error
System.out.println(badLocale); // It prints a_A
So it's good to know that Locale class also provides predefined constants for some common languages and countries, for example:
Locale.GERMAN
Locale.KOREAN
Locale.UK
Locale.ITALY
For the exam, you don't have to know all these constants, or some obscure language and country codes, just that there are four ways to start working with locales.
Once you have a Locale object, you can change the locale of your program with the setDefault(Locale) method:
System.out.println(Locale.getDefault()); // Prints let's say en_GB
Locale.setDefault(new Locale("en", "US"));
System.out.println(Locale.getDefault()); // Now prints en_US
Property files define strings in key/value pairs separated by lines.
There are some rules, like:
# or ! will be treated as a comment.For example, we can have the following file:
Messages.properties
# Video related messages
video.added = The video has been added
video.deleted = The video has been deleted
To read it, you create an instance of java.util.Properties and load it with either a java.io.Reader or a java.io.InputStream, for example:
Properties prop = new Properties();
try (InputStream is = getClassLoader()
.getResourceAsStream("Messages.properties")) {
prop.load(is); // Load properties
// Prints The video has been adde
System.out.println(prop.getProperty("video.added"));
// It prints a default value if the key is not foun
System.out.println(prop.getProperty("video.add", "default"));
// Get all properties keys
Enumeration<?> e = prop.propertyNames();
} catch (IOException e) {
e.printStackTrace();
}
To localize an application, we have Resource Bundles, which define a set of keys with localized values. Resource Bundles can be property files or classes.
To support this, we have an abstract class java.util.ResourceBundle with two subclasses:
java.util.PropertyResourceBundle
Each locale is represented by a property file. Keys and values are of type String.
java.util.ListResourceBundle
Each locale is represented by a subclass of this class that overrides the method Object[][] getContents(). The returned array represents the keys and values. Keys must be of type String, but values can be any object.
In both methods, the name (of the file or the class) follows a convention which allows Java to search for resource bundles and match them to their corresponding locales.
That name convention is:
package.Bundle_language_country_variant
For example:
com.example.MyBundle_fr_FR
Only the resource bundle name is required (and the name of the package if it is not the default one).
For example, we can have bundles with the following names (assuming we're working with property files, although it's the same with classes):
MyBundle.properties
MyBundle_en.properties
MyBundle_en_NZ.properties
MyBundle_en_US.properties
To determine which bundle belongs to a particular locale, Java tries to find the most specific bundle that matches the properties of the locale.
This means that:
1. Java first searches for a bundle whose name matches the complete locale:
package.bundle_language_country_variant
2. If it cannot find one, it drops the last component of the name and repeats the search:
package.bundle_language_country
3. If it cannot find one, again, it drops the last component of the name and repeats the search:
package.bundle_language
4. If still cannot find one, the last component is dropped again, leaving just the name of the bundle:
package.bundle
If nothing is found, a MissingBundleException is thrown.
If a class and a property file share the same name, Java gives priority to the class.
But there's another important point.
In your program, you can use the keys of the matching resource bundle and ANY of its PARENTS.
The parents of a resource bundle are the ones with the same name but fewer components. For example, the parents of MyBundle_es_ES are:
MyBundle_es
MyBundle
For example, let's assume the default locale en_US, and that your program is using those and other property files, all in the default package, with the values:
MyBundle_EN.properties
s = buddy
MyBundle_es_ES.properties
s = tío
MyBundle_es.properties
s = amigo
MyBundle.properties
hi = Hola
We can create a resource bundle like this:
public class Test {
public static void main(String[] args) {
Locale spain = new Locale("es", "ES");
Locale spanish = new Locale("es");
ResourceBundle rb = ResourceBundle.getBundle("MyBundle", spain);
System.out.format("%s %s\n",
rb.getString("hi"), rb.getString("s"));
rb = ResourceBundle.getBundle("MyBundle", spanish);
System.out.format("%s %s\n",
rb.getString("hi"), rb.getString("s"));
}
}
The output:
Hola tío
Hola amigo
As you can see, each locale picks different values for key s, but they both use the same for hi since this key is defined in their parent.
If you don't specify a locale, the ResourceBundle class will use the default locale of your system:
ResourceBundle rb = ResourceBundle.getBundle("MyBundle");
System.out.format("%s %s\n",
rb.getString("hi"), rb.getString("s"));
Since we assume that the default locale is en_US, the output is:
Hola buddy
We can also get all the keys in a resource bundle with the method keySet():
ResourceBundle rb =
ResourceBundle.getBundle("MyBundle", spain);
Set<String> keys = rb.keySet();
keys.stream()
.forEach(key ->
System.out.format("%s %s\n", key, rb.getString(key)));
The output (notice it also prints the parent key):
hi Hola
s tío
If instead of using property files we were using classes, the program would look like this:
package bundles;
public class MyBundle_EN extends ListResourceBundle {
@Override
protected Object[][] getContents() {
return new Object[][] {
{ "s", "buddy" }
};
}
}
package bundles;
public class MyBundle_es_ES extends ListResourceBundle {
@Override
protected Object[][] getContents() {
return new Object[][] {
{ "s", "tío" }
};
}
}
package bundles;
public class MyBundle_es extends ListResourceBundle {
@Override
protected Object[][] getContents() {
return new Object[][] {
{ "s", "amigo" }
};
}
}
package bundles;
public class MyBundle extends ListResourceBundle {
@Override
protected Object[][] getContents() {
return new Object[][] {
{ "hi", "Hola" }
};
}
}
public class Test {
public static void main(String[] args) {
Locale spain = new Locale("es", "ES");
Locale spanish = new Locale("es");
ResourceBundle rb =
ResourceBundle.getBundle("bundles.MyBundle", spain);
System.out.format("%s %s\n",
rb.getString("hi"), rb.getString("s"));
rb = ResourceBundle.getBundle("bundles.MyBundle", spanish);
System.out.format("%s %s\n",
rb.getString("hi"), rb.getString("s"));
}
}
The only thing that changed in the Test class was the name of the bundle (we had to reference the package). This should not surprise you, after all, both PropertyResourceBundle and ListResourceBundle inherit from the same class.
Remember also, when using classes we can have values of types other than String, for example:
public class MyBundle extends ListResourceBundle {
@Override
protected Object[][] getContents() {
return new Object[][] {
{ "hi", "Hola" },
{ "number", new Integer(100) }
};
}
}
To get an object value, we use:
Integer num = (Integer)rb.getObject("number");
Instead of rb.getString(key). In fact, this method is just a shortcut to:
String val = (String)rb.getObject("hi");
java.util.Locale class basically represents a language and a country, and is the starting point for localization in Java.Locale locale = Locale.getDefault();Locale [] locales = Locale.getAvailableLocales();Locale object using a constructor:Locale(String language)
Locale(String language, String country)
Locale(String language, String country, String variant)forLanguageTag(String) factory method: Locale german = Locale.forLanguageTag("de");Locale.Builder: Locale japan = new Locale.Builder() .setRegion("JP") .setLanguage("jp") .build();Locale.GERMAN
Locale.KOREANLocale object, you can change the locale of your program with the setDefault(Locale) method: Locale.setDefault(new Locale("en", "US"));Object[][] getContents(). The returned array represents the keys and values. Keys must be of type String, but values can be any object.MissingBundleException is thrown.1. Given:
public class Question_30_1 {
public static void main(String[] args) {
Locale locale = new Locale("", "");
ResourceBundle rb = ResourceBundle.getBundle("Bundle1", locale);
System.out.println(rb.getString("key1"));
}
}
Bundle1.properties
key1 = Hi
What is the result?
A. Hi
B. null
C. Compilation fails
D. An exception occurs at runtime
2. Which of the following are valid ways to create a locale?
A. new Locale();
B. Locale.Builder().setLanguage("de");
C. new Locale.Builder().setRegion("DE").build();
D. Locale.forRegionTag("it");
3. Assuming a default locale de_DE, which of the following resource bundles will be loaded first with
ResourceBundle rb = ResourceBundle.getBundle("MyBundle");
A. MyBundle.class
B. MyBundle.properties
C. MyBundle_de.class
D. MyBundle_de.properties
4. Given:
public class Question_30_4 {
public static void main(String[] args) {
Locale locale = new Locale("en", "CA");
System.out.println(locale.toLanguageTag());
}
}
What is the result?
A. en
B. en_CA
C. CA
D. CA_en
5. Which of the following are valid ways to get a value given its key from a property file resource bundle rb?
A. rb.getValue("key");
B. rb.getProperty("key");
C. rb.getObject("key");
D. rb.get("key");