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BAEL-4209: Difference between e.getMessage() and e.getLocalizedMessage() (eugenp#10222)
* - initial commit of sample code * BAEL-4209: Moving the localized exception module into core-java-exceptions-3. * BAEL-4209: Removed the old files for localizing exception messages.
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‎core-java-modules/core-java-exceptions-3/src/main/java/com/baeldung/exceptions/localization/LocalizedException.java‎

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package com.baeldung.exceptions.localization;
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import java.util.Locale;
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public class LocalizedException extends Exception {
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private static final long serialVersionUID = 1L;
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private final String messageKey;
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private final Locale locale;
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public LocalizedException(String messageKey) {
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this(messageKey, Locale.getDefault());
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}
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public LocalizedException(String messageKey, Locale locale) {
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this.messageKey = messageKey;
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this.locale = locale;
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}
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/**
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* @return a localized message based on the messageKey provided at instantiation.
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*/
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public String getMessage() {
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/*
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* This is a deliberate role reversal of the default implementation of getLocalizedMessage.
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* some logging frameworks like Log4J 1 & 2 and Logback will use getMessage instead of
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* getLocalizedMessage when logging Throwables. If we want to use these frameworks in client
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* applications to log localized messages, then we'll need to override getMessage in a
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* similar fashion to return the appropriate content. Or, you can call getLocalizedMessage
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* on your own to create the log content.
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*/
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return getLocalizedMessage();
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}
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/**
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* @return a localized message based on the messageKey provided at instantiation.
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*/
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public String getLocalizedMessage() {
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/*
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* java.util.logging uses getLocalizedMessage when logging Throwables.
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*/
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return Messages.getMessageForLocale(messageKey, locale);
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}
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}

‎core-java-modules/core-java-exceptions-3/src/main/java/com/baeldung/exceptions/localization/Messages.java‎

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package com.baeldung.exceptions.localization;
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import java.util.Locale;
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import java.util.ResourceBundle;
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public class Messages {
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/**
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* Retrieves the value for the messageKey from the locale-specific messages.properties, or from
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* the base messages.properties for unsupported locales.
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*
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* @param messageKey The key for the message in the messages.properties ResourceBundle.
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* @param locale The locale to search the message key.
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* @return The value defined for the messageKey in the provided locale.
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*/
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public static String getMessageForLocale(String messageKey, Locale locale) {
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/*
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* For more complex implementations, you will want a var-args parameter for MessageFormat
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* substitutions. Then we can read the value from the bundle and pass the value with the
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* substitutions to MessageFormat to create the final message value.
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*/
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return ResourceBundle.getBundle("messages", locale)
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.getString(messageKey);
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}
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}

‎core-java-modules/core-java-exceptions-3/src/main/resources/messages.properties‎

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message.exception = I am an exception.

‎core-java-modules/core-java-exceptions-3/src/main/resources/messages_fr.properties‎

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message.exception = Je suis une exception.

‎core-java-modules/core-java-exceptions-3/src/test/java/com/baeldung/exceptions/localization/LocalizedExceptionUnitTest.java‎

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package com.baeldung.exceptions.localization;
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import org.junit.After;
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import org.junit.Before;
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import org.junit.Test;
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import java.util.Locale;
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import static org.assertj.core.api.Assertions.assertThat;
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public class LocalizedExceptionUnitTest {
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private Locale originalDefaultLocale;
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@Before
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public void saveOriginalDefaultLocale() {
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originalDefaultLocale = Locale.getDefault();
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}
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@After
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public void restoreOriginalDefaultLocale() {
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Locale.setDefault(originalDefaultLocale);
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}
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@Test
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public void givenUsEnglishDefaultLocale_whenLocalizingMessage_thenMessageComesFromDefaultMessages() {
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Locale.setDefault(Locale.US);
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LocalizedException localizedException = new LocalizedException("message.exception");
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String usEnglishLocalizedExceptionMessage = localizedException.getLocalizedMessage();
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assertThat(usEnglishLocalizedExceptionMessage).isEqualTo("I am an exception.");
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}
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@Test
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public void givenFranceFrenchDefaultLocale_whenLocalizingMessage_thenMessageComesFromFrenchTranslationMessages() {
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Locale.setDefault(Locale.FRANCE);
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LocalizedException localizedException = new LocalizedException("message.exception");
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String franceFrenchLocalizedExceptionMessage = localizedException.getLocalizedMessage();
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assertThat(franceFrenchLocalizedExceptionMessage).isEqualTo("Je suis une exception.");
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}
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@Test
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public void givenUsEnglishProvidedLocale_whenLocalizingMessage_thenMessageComesFromDefaultMessage() {
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LocalizedException localizedException = new LocalizedException("message.exception", Locale.US);
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String usEnglishLocalizedExceptionMessage = localizedException.getLocalizedMessage();
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assertThat(usEnglishLocalizedExceptionMessage).isEqualTo("I am an exception.");
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}
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@Test
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public void givenFranceFrenchProvidedLocale_whenLocalizingMessage_thenMessageComesFromFrenchTranslationMessages() {
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LocalizedException localizedException = new LocalizedException("message.exception", Locale.FRANCE);
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String franceFrenchLocalizedExceptionMessage = localizedException.getLocalizedMessage();
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assertThat(franceFrenchLocalizedExceptionMessage).isEqualTo("Je suis une exception.");
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}
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}

‎core-java-modules/core-java-exceptions-3/src/test/java/com/baeldung/exceptions/localization/MessagesUnitTest.java‎

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package com.baeldung.exceptions.localization;
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import org.junit.Test;
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import java.util.Locale;
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import static org.assertj.core.api.Assertions.assertThat;
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public class MessagesUnitTest {
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@Test
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public void givenUsEnglishLocale_whenRetrievingMessage_thenEnglishTranslationIsReturned() {
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String translatedMessage = Messages.getMessageForLocale("message.exception", Locale.US);
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assertThat(translatedMessage).isEqualTo("I am an exception.");
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}
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@Test
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public void givenFranceFrenchLocale_whenRetrievingMessage_thenFrenchTranslationIsReturned() {
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String translatedMessage = Messages.getMessageForLocale("message.exception", Locale.FRANCE);
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assertThat(translatedMessage).isEqualTo("Je suis une exception.");
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}
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}

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