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Java Internationalization : Isolating Locale-Specific Data With Resource Bundles

A property resource bundle is a collection of text elements in a properties file format
stored in a .properties file. The PropertyResourceBundle class provides all code
necessary for you to access these resources in a locale-dependent manner.

Example 4-10 illustrates basic property file formatting. The Properties class in the
java. util package handles reading and writing properties files. Both the keys to
lookup a value and the values returned are Java Strings. Example 4- 10 shows a
simple properties file.

Example 4-10. A Properties File

# Sample properties file for demonstrating PropertyResourceBundle class
#
# Text that will appear in the title bar of our application
ApplicationTitle= Demonstrating the use of PropertyResourceBundle
#
# Text that will be displayed on OK buttons
OKButtonLabel= OK
#
# Text for display on a button to cancel current operation
CancelButtonLabel= Cancel
#
#

A property in a properties file is specified in the following format: Key= Value

In most properties files, you see that the separator between key and value is the equals sign (=) character. Java also allows use of the colon (:) character as a separator between key and value, as in: Key: Value

We won't go into all the details about how Java deals with properties files, but here are a few general comments on how properties files are structured: lines starting with an exclamation (!) or a pound (#) character are ignored when the properties file is read. These characters indicate that the line is a comment line. Keys are case sensitive. Finally, you can specify values in a properties file that span multiple lines by using a backslash ( \ ) to indicate line continuation. Example 4-11 illustrates this point.

Example 4-11. Properties File Where Values Span More Than One Line (AnimalResources. properties)

# Sample properties file with keys whose values span more than one line
#
Animals= Cat, Dog, Giraffe, \
Shark, Dolphin, Bird, \
Bear, Moose

If you retrieved the "Animals" key, you'd get back the value Cat, Dog, Giraffe, Shark, Dolphin, Bird, Bear, Moose. All the leading whitespace on any continuation line is discarded. You could then, for example, break up the value returned to you by using the java. util. StringTokenizer class.

Example 4-12 uses the properties file from Example 4-11 to print a list of animal names.

Example 4-12. Printing a List of Animals Stored in a Properties Resource File

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

public class Animals {

  public static void main( String [] argv) {

    ResourceBundle animalResources;

    try {
      animalResources = ResourceBundle. getBundle(
        "AnimalResources", Locale. getDefault());
      System. out. println( animalResources. getString(" Animals"));
    } catch (MissingResourceException mre) {
      mre. printStackTrace();
    }
  }
}

Here is the output produced after running Example 4-12:

C:\> java Animals

Cat, Dog, Giraffe, Shark, Dolphin, Bird, Bear, Moose

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