JAVA EE: MessageSource

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Monday, 27 August 2018

Spring MessageSourceAware Java Bean Example | Spring Tutorial | Spring Framework

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Overview: MessageSourceAware in Spring

Internationalization (i18n) and localization (l10n) are essential features for enterprise applications that serve multi-language audiences. In the Spring Framework, message resolution is handled via the MessageSource interface. To allow a Spring bean to resolve internationalized messages directly without tight coupling to the entire container context, Spring provides the MessageSourceAware callback interface.

In this guide, you will learn how the MessageSourceAware interface works, how Spring injects the MessageSource bean during initialization, and how to resolve parameterized, localized messages cleanly.

Understanding MessageSourceAware

The MessageSourceAware interface is a member of Spring's Aware interfaces family designed specifically for message management:

Lifecycle Injection: When a bean implements MessageSourceAware, Spring calls its setMessageSource(MessageSource messageSource) method after property population and before initialization callbacks.
Targeted Scope: It provides access strictly to message resolution capabilities, keeping beans focused on their responsibilities without needing a complete ApplicationContext reference.
Support for Localization: Works seamlessly with ResourceBundleMessageSource or ReloadableResourceBundleMessageSource to look up locale-specific text using keys and parameters.

Step-by-Step Implementation

Implement the Interface: Have your bean implement org.springframework.context.MessageSourceAware.
Override setMessageSource(): Save the injected MessageSource instance in a field:
public void setMessageSource(MessageSource messageSource) { this.messageSource = messageSource; }
Resolve Messages: Use the getMessage() method to retrieve locale-specific messages by passing the message key, arguments, and target Locale.

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Spring MessageSourceAware Java Bean Example | Spring Tutorial | Spring Framework

pom.xml

<project xmlns="http://maven.apache.org/POM/4.0.0" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"

    xsi:schemaLocation="http://maven.apache.org/POM/4.0.0%20http://maven.apache.org/maven-v4_0_0.xsd">

    <modelVersion>4.0.0</modelVersion>

    <groupId>com.ram.core</groupId>

    <artifactId>SpringDemo</artifactId>

    <packaging>jar</packaging>

    <version>1.0-SNAPSHOT</version>

    <name>SpringDemo</name>

    <url>http://maven.apache.org</url>

    <properties>

        <spring.version>5.0.2.RELEASE</spring.version>

    </properties>

    <dependencies>

        <dependency>

            <groupId>junit</groupId>

            <artifactId>junit</artifactId>

            <version>3.8.1</version>

            <scope>test</scope>

        </dependency>

        <!-- Spring 5 dependencies -->

        <dependency>

            <groupId>org.springframework</groupId>

            <artifactId>spring-core</artifactId>

            <version>${spring.version}</version>

        </dependency>

        <dependency>

            <groupId>org.springframework</groupId>

            <artifactId>spring-context</artifactId>

            <version>${spring.version}</version>

        </dependency>

    </dependencies>

</project>

messages_en_US.properties

greeting=hello

messages_fr.properties

greeting=Bonjour

MessageSourceAwareImpl.java

package com.ram.aware;

import java.util.Locale;

import org.springframework.context.MessageSource;

import org.springframework.context.MessageSourceAware;

public class MessageSourceAwareImpl implements MessageSourceAware

{

    private MessageSource messageSource;

    public void setMessageSource(MessageSource messageSource)

    {

        System.out.println(

                "setMessageSource(MessageSource messageSource) is called "

                        + "by the Spring Container");

        this.messageSource = messageSource;

    }

    public void displayMessagesSpecificToLocale()

    {

        String englishGreet = messageSource.getMessage("greeting", null,

                Locale.US);

        System.out.println("Greeting in English = " + englishGreet);

        String frenchGreet = messageSource.getMessage("greeting", null,

                Locale.FRENCH);

        System.out.println("Greeting in French  = " + frenchGreet);

    }

}

applicationContext.xml

<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-4.3.xsd">

    <bean id="messageSourceAware" class="com.ram.aware.MessageSourceAwareImpl" />

    <bean id="messageSource"

        class="org.springframework.context.support.ReloadableResourceBundleMessageSource">

        <property name="basename" value="classpath:messages" />

        <property name="defaultEncoding" value="UTF-8" />

    </bean>

</beans>

App.java

package com.ram.core;

import org.springframework.context.support.ClassPathXmlApplicationContext;

import com.ram.aware.MessageSourceAwareImpl;

public class App

{

    public static void main(String[] args)

    {

        ClassPathXmlApplicationContext applicationContext = new ClassPathXmlApplicationContext(

                "applicationContext.xml");

        MessageSourceAwareImpl messageSourceAwareImpl = applicationContext

                .getBean("messageSourceAware", MessageSourceAwareImpl.class);

        System.out.println("messageSourceAwareImpl = "+messageSourceAwareImpl);

        messageSourceAwareImpl.displayMessagesSpecificToLocale();

        applicationContext.close();

    }

}

Output

Aug 12, 2018 1:26:05 PM org.springframework.context.support.AbstractApplicationContext prepareRefresh

INFO: Refreshing org.springframework.context.support.ClassPathXmlApplicationContext@5b37e0d2: startup date [Sun Aug 12 13:26:05 IST 2018]; root of context hierarchy

Aug 12, 2018 1:26:05 PM org.springframework.beans.factory.xml.XmlBeanDefinitionReader loadBeanDefinitions

INFO: Loading XML bean definitions from class path resource [applicationContext.xml]

setMessageSource(MessageSource messageSource) is called by the Spring Container

messageSourceAwareImpl = com.ram.aware.MessageSourceAwareImpl@1ce92674

Greeting in English = hello

Greeting in French  = Bonjour

Aug 12, 2018 1:26:06 PM org.springframework.context.support.AbstractApplicationContext doClose

INFO: Closing org.springframework.context.support.ClassPathXmlApplicationContext@5b37e0d2: startup date [Sun Aug 12 13:26:05 IST 2018]; root of context hierarchy