Spring and Message Loading

One of the advantages of using the application context is that we can load locale specific messages using the ApplicationContext. More simply put Spring includes Localization and Internationalization support.
Internationalization or I18N is defined in wikipedia as
the process of designing a software application so that it can be adapted to various languages and regions without engineering changes.
Localization or L10N is defined as
process of adapting internationalized software for a specific region or language by adding locale-specific components and translating text.
The ApplicationContext implements the MessageSource interface for resolving messages. It includes support for parameters and also locale based selection of such messages. To start of I created a set of property files:

The contents of the property files is as below:
standard.properties

rockMessage=Alligators rock!

failure.properties

argument.required=The \''{0}\'' argument is required.

failure_en_GB.properties

argument.required=This is Great Britan and the \''{0}\''is required, I insist required.

Next the step is to create a MessageSource bean and pass it the list of our property files.

<beans xmlns="http://www.springframework.org/schema/beans"
xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
xsi:schemaLocation="http://www.springframework.org/schema/beans
http://www.springframework.org/schema/beans/spring-beans-2.5.xsd">
    <bean id="messageSource"
        class="org.springframework.context.support.ResourceBundleMessageSource">
        <property name="basenames">
            <list>
                <value>standard</value>
                <value>com/resources/failure</value>
            </list>
        </property>
    </bean>
</beans>

The implementation used here is ResourceBundleMessageSource. This class is built on the top of the Java resource bundle. The class uses JDK's standard message parsing provided by MessageFormat. The bean has a property called "basenames" which takes a list of property files. The failure property file needs to be included only once. Both “failure_en_US.properties” and “failure_en_GB.properties” are consider one file in Spring. We just need to include the file name once, and Spring will find the correct locale automatically.
I decided to test the working of the bean:

public static void main(String[] args) {
    ApplicationContext applicationContext = new ClassPathXmlApplicationContext(
            "spring-locale.xml");
    System.out.println(applicationContext.getMessage("rockMessage", null,
            "Default", null));
}

The application context's getMessage method takes four parameters:String code, Object[] args, String defaultMessage, Locale locale

• The code is the name of the property. 
• If the message is parametrized, then the parameter values are passed in the second array. 
• The third parameter is the default message used when the property is not found. 
• The fourth indicates the locale to use. 

The application context internally delegates the call to the MessageSource implementation. For rendering of no-arg messages, it does not use MessageFormat class.The output of the code is as below:

Alligators rock!

When the ApplicationContext gets loaded, it automatically searches for a MessageSource bean defined in the context. The bean has to have the name/id 'messageSource'.If such a bean is found, all calls to the methods described above will be delegated to the message source that was found. I tested the same method for parametrized message

public static void main(String[] args) {
    ApplicationContext applicationContext = new ClassPathXmlApplicationContext(
        "spring-locale.xml");
    //passing parameters to the message
    System.out.println(applicationContext.getMessage("argument.required",
        new Object[] { "Aplication Context" }, "Required", null));
}

The output of the same is :

The 'Aplication Context' argument is required.

I tested the code for UK locale:

public static void main(String[] args) {
    ApplicationContext applicationContext = new ClassPathXmlApplicationContext(
        "spring-locale.xml");
    // passing parameters to the message for a specific locale
    System.out.println(applicationContext.getMessage("argument.required",
        new Object[] { "Aplication Context" }, "Required", Locale.UK));
}

The output of the same is

This is Great Britan  and the 'Aplication Context' is required, I insist required.

As per the Spring documentation,

The caching provided by this MessageSource is significantly 
faster than the built-in caching of the java.util.ResourceBundle class.

In the next post we will have a look at reloading the message bundles.