Dealing with Compound Messages
MessageFormat object, and
store this pattern in a ResourceBundle.
By stepping through a sample program, this section demonstrates how to
internationalize a compound message. The sample program makes use of
the
MessageFormat class.
The full source code for this program is in the file called
MessageFormatDemo.java.
The German locale properties are in the file called
MessageBundle_de_DE.properties.
1. Identify the Variables in the Message
Suppose that you want to internationalize the following message:
Notice that we've underlined the variable data and have identified what kind of objects will represent this data.
2. Isolate the Message Pattern in a ResourceBundle
Store the message in aResourceBundle named
MessageBundle, as follows:
ResourceBundle messages =
ResourceBundle.getBundle("MessageBundle", currentLocale);
This ResourceBundle is backed by a properties file for
each Locale. Since the ResourceBundle is
called MessageBundle, the properties file for U.S. English
is named MessageBundle_en_US.properties. The contents of
this file is as follows:
template = At {2,time,short} on {2,date,long}, we detected \
{1,number,integer} spaceships on the planet {0}.
planet = Mars
The first line of the properties file contains the message pattern. If
you compare this pattern with the message text shown in step 1, you'll
see that an argument enclosed in braces replaces each variable in the
message text. Each argument starts with a digit called the argument
number, which matches the index of an element in an Object
array that holds the argument values. Note that in the pattern the
argument numbers are not in any particular order. You can place the
arguments anywhere in the pattern. The only requirement is that the
argument number have a matching element in the array of argument
values.
The next step discusses the argument value array, but first let's look at each of the arguments in the pattern. The following table provides some details about the arguments:
| Argument | Description |
|---|---|
{2,time,short}
|
The time portion of a Date object. The short
style specifies the DateFormat.SHORT formatting style.
|
{2,date,long}
|
The date portion of a Date
object. The same Date
object is used for both the date and time variables.
In the Object array of arguments the index of the element
holding the Date
object is 2. (This is described in the next step.)
|
{1,number,integer}
|
A Number object,
further qualified with the integer number style.
|
{0}
|
The String
in the ResourceBundle
that corresponds to the planet key.
|
For a full description of the argument syntax, see the API documentation for the
MessageFormat class.
3. Set the Message Arguments
The following lines of code assign values to each argument in the pattern. The indexes of the elements in themessageArguments array match the argument numbers in the
pattern. For example, the Integer element at index 1
corresponds to the {1,number,integer} argument in the
pattern. Because it must be translated, the String object
at element 0 will be fetched from the ResourceBundle with
the getString method. Here is the code that defines the
array of message arguments:
Object[] messageArguments = {
messages.getString("planet"),
new Integer(7),
new Date()
};
4. Create the Formatter
Next, create aMessageFormat object. You set the
Locale because the message contains Date and
Number objects, which should be formatted in a
locale-sensitive manner.
MessageFormat formatter = new MessageFormat("");
formatter.setLocale(currentLocale);
5. Format the Message Using the Pattern and the Arguments
This step shows how the pattern, message arguments, and formatter all work together. First, fetch the patternString from the
ResourceBundle with the getString method.
The key to the pattern is template. Pass the pattern
String to the formatter with the applyPattern
method. Then format the message using the array of message
arguments, by invoking the format method. The
String returned by the format method is ready
to be displayed. All of this is accomplished with just two lines of
code:
formatter.applyPattern(messages.getString("template"));
String output = formatter.format(messageArguments);
6. Run the Demo Program
The demo program prints the translated messages for the English and German locales and properly formats the date and time variables. Note that the English and German verbs ("detected" and "entdeckt") are in different locations relative to the variables:currentLocale = en_US At 10:16 AM on July 31, 2009, we detected 7 spaceships on the planet Mars. currentLocale = de_DE Um 10:16 am 31. Juli 2009 haben wir 7 Raumschiffe auf dem Planeten Mars entdeckt.
