ICU4J Locale Service Provider

Overview

Java SE 6 introduced a new feature which allows Java user code to extend locale support in Java runtime environment. JREs shipped by Oracle or IBM come with decent locale coverage, but some users may want more locale support. Java SE 6 includes abstract classes extending java.util.spi.LocaleServiceProvider. Java SE 6 users can create a subclass of these abstract class to supply their own locale support for text break, collation, date/number formatting or providing translations for currency, locale and time zone names.

ICU4J has been providing more comprehensive locale coverage than standard JREs. However, Java programmers have to use ICU4J's own internationalization service APIs (com.ibm.icu.*) to utilize the rich locale support.  Sometimes, the migration is not an option for various reasons.  For example, your code may depend on existing Java libraries utilizing JDK internationalization service APIs, but you have no access to the source code.  In this case, it is not possible to modify the libraries to use ICU4J APIs.

ICU4J Locale Service Provider is a component consists of classes implementing the Java SE 6 locale sensitive service provider interfaces.  Available service providers are -
ICU4J Locale Service Provider is designed to work as installed extensions in a JRE. Once the component is configured properly, Java application running on the JRE automatically picks the ICU4J's internationalization service implementation when a requested locale is not available in the JRE.

Using ICU4J Locale Service Provider

Java SE 6 locale sensitive service providers are using the Java Extension Mechanism. An implementation of a locale sensitive service provider is installed as an optional package to extend the functionality of the Java core platform. To install an optional package, its JAR files must be placed in the Java extension directory. The standard location is <java-home>/lib/ext. You can alternatively use the system property java.ext.dirs to specify one or more locations where optional packages are installed. For example, if the JRE root directry is JAVA_HOME and you put ICU4J Locale Service Provider files in ICU_SPI_DIR, the ICU4J Locale Service Provider is enabled by the following command.

java -Djava.ext.dirs=%JAVA_HOME%\lib\ext;%ICU_SPI_DIR% <your_java_app>  [Microsoft Windows]
java -Djava.ext.dirs=$JAVA_HOME/lib/ext:$ICU_SPI_DIR <your_java_app>    [Linux, Solaris and other unix like platforms]

The ICU4J's implementations of Java SE 6 locale sensitive service provider interfaces and configuration files are packaged in a single JAR file (icu4j-localespi-<version>.jar). But the actual implementation of the service classes and data are in the ICU4J core JAR file (icu4j-<version>.jar).  So you need to put the localespi JAR file along with the core JAR file in the Java extension directory.

Once the ICU4J Locale Service Provider is installed properly, factory methods in JDK internationalization classes look for the implementation provided by ICU4J when a requested locale is not supported by the JDK service class.  For example, locale af_ZA (Afrikaans - South Africa) is not supported by JDK DateFormat in Oracle Java SE 6. The following code snippet returns an instance of DateFormat from ICU4J Locale Service Provider and prints out the current date localized for af_ZA.

DateFormat df = DateFormat.getDateInstance(DateFormat.LONG, new Locale("af", "ZA"));
System.out.println(df.format(new Date()));

Sample output:

2008 Junie 19     [With ICU4J Locale Service Provider enabled]
June 19, 2008     [Without ICU4J Locale Service Provider]

Optional Configuration

Enabling or disabling individual service

By default, all Java 6 SE locale sensitive service providers are enabled in the ICU4J Locale Service Provider JAR file.  If you want to disable specific providers supported by ICU4J, you can remove the corresponding provider configuration files from META-INF/services in the localespi JAR file.  For example, if you do not want to use ICU's time zone name service at all, you can remove the file: META-INF/services/java.util.spi.TimeZoneNameProvider from the JAR file.

Note: Disabling DateFormatSymbolsProvider/DecimalFormatSymbolsProvider won't affect the localized symbols actually used by DateFormatProvider/NumberFormatProvider by the current implementation.  These services are implemented independently.

Configuring the behavior of ICU4J Locale Service Provider

com/ibm/icu/impl/javaspi/ICULocaleServiceProviderConfig.properties in the localespi JAR file is used for configuring the behavior of the ICU4J Locale Service Provider implementation.  There are some configuration properties available.  See the table below for each configuration in detail.

 Property Value Default Description
 com.ibm.icu.impl.javaspi.ICULocaleServiceProvider.enableIcuVariants "true" or "false"  "true" Whether if Locales with ICU's variant suffix will be included in getAvailableLocales. The current Java SE 6 locale sensitive service does not allow user provided provider implementations to override locales supported by JRE itself. When this property is "true"(default), ICU4J Locale Service Provider includes Locales with the suffix(com.ibm.icu.impl.javaspi.ICULocaleServiceProvider.icuVariantSuffix) in the variant field. For example, the ICU4J provider includes locales fr_FR and fr_FR_ICU4J in the available locale list. So JDK API user can still access the internationalization service object created by the ICU4J provider by the special locale fr_FR_ICU4J.
 com.ibm.icu.impl.javaspi.ICULocaleServiceProvider.icuVariantSuffix Any String "ICU4J" (49 or later)
 "ICU" (before 49)
 Suffix string used in Locale's variant field to specify the ICU implementation.
 com.ibm.icu.impl.javaspi.ICULocaleServiceProvider.enableIso3Languages "true" or "false" "true" Whether if 3-letter language Locales are included in getAvailabeLocales. Use of 3-letter language codes in java.util.Locale is not supported by the API reference document. However, the implementation does not check the length of language code, so there is no practical problem with it.
 com.ibm.icu.impl.javaspi.ICULocaleServiceProvider.useDecimalFormat "true" or "false" "false" Whether if java.text.DecimalFormat subclass is used for NumberFormat#getXXXInstance. DecimalFormat#format(Object,StringBuffer,FieldPosition) is declared as final, so ICU cannot override the implementation. As a result, some number types such as BigInteger/BigDecimal are not handled by the ICU implementation. If a client expects NumberFormat#getXXXInstance returns a DecimalFormat (for example, need to manipulate decimal format patterns), he/she can set true to this setting. However, in this case, BigInteger/BigDecimal support is not done by ICU's implementation.


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