GNU gettext utilities: Java
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15.5.3 Java
- RPMs
- java, java2
- Ubuntu packages
- default-jdk
- File extension
java
- String syntax
- "abc", """text block"""
- gettext shorthand
- i18n("abc")
- gettext/ngettext functions
GettextResource.gettext
,GettextResource.ngettext
,GettextResource.pgettext
,GettextResource.npgettext
- textdomain
- —, use
ResourceBundle.getResource
instead - bindtextdomain
- —, use CLASSPATH instead
- setlocale
- automatic
- Prerequisite
- —
- Use or emulate GNU gettext
- —, uses a Java specific message catalog format
- Extractor
xgettext -ki18n
- Formatting with positions
MessageFormat.format "{1,number} {0,number}"
orString.format "%2$d %1$d"
- Portability
- fully portable
- po-mode marking
- —
Before marking strings as internationalizable, uses of the string concatenation operator need to be converted to MessageFormat
applications. For example, "file "+filename+" not found"
becomes MessageFormat.format("file {0} not found", new Object[] { filename })
. Only after this is done, can the strings be marked and extracted.
GNU gettext uses the native Java internationalization mechanism, namely ResourceBundle
s. There are two formats of ResourceBundle
s: .properties
files and .class
files. The .properties
format is a text file which the translators can directly edit, like PO files, but which doesn’t support plural forms. Whereas the .class
format is compiled from .java
source code and can support plural forms (provided it is accessed through an appropriate API, see below).
To convert a PO file to a .properties
file, the msgcat
program can be used with the option --properties-output
. To convert a .properties
file back to a PO file, the msgcat
program can be used with the option --properties-input
. All the tools that manipulate PO files can work with .properties
files as well, if given the --properties-input
and/or --properties-output
option.
To convert a PO file to a ResourceBundle class, the msgfmt
program can be used with the option --java
or --java2
. To convert a ResourceBundle back to a PO file, the msgunfmt
program can be used with the option --java
.
Two different programmatic APIs can be used to access ResourceBundles. Note that both APIs work with all kinds of ResourceBundles, whether GNU gettext generated classes, or other .class
or .properties
files.
- The
java.util.ResourceBundle
API. In particular, its getString function returns a string translation. Note that a missing translation yields a MissingResourceException. This has the advantage of being the standard API. And it does not require any additional libraries, only the msgcat generated .properties files or the msgfmt generated .class files. But it cannot do plural handling, even if the resource was generated by msgfmt from a PO file with plural handling. - The
gnu.gettext.GettextResource
API. Reference documentation in Javadoc 1.1 style format is in the javadoc2 directory. Its gettext function returns a string translation. Note that when a translation is missing, the msgid argument is returned unchanged. This has the advantage of having the ngettext function for plural handling and the pgettext and npgettext for strings constraint to a particular context. To use this API, one needs the libintl.jar file which is part of the GNU gettext package and distributed under the LGPL.
Four examples, using the second API, are available in the examples
directory: hello-java
, hello-java-awt
, hello-java-swing
, hello-java-qtjambi
.
Now, to make use of the API and define a shorthand for ‘getString
’, there are three idioms that you can choose from:
(This one assumes Java 1.5 or newer.) In a unique class of your project, say ‘
Util
’, define a static variable holding theResourceBundle
instance and the shorthand:private static ResourceBundle myResources = ResourceBundle.getBundle("domain-name"); public static String i18n(String s) { return myResources.getString(s); }
All classes containing internationalized strings then contain
import static Util.i18n;
and the shorthand is used like this:
System.out.println(i18n("Operation completed."));
In a unique class of your project, say ‘
Util
’, define a static variable holding theResourceBundle
instance:public static ResourceBundle myResources = ResourceBundle.getBundle("domain-name");
All classes containing internationalized strings then contain
private static ResourceBundle res = Util.myResources; private static String i18n(String s) { return res.getString(s); }
and the shorthand is used like this:
System.out.println(i18n("Operation completed."));
You add a class with a very short name, say ‘
S
’, containing just the definition of the resource bundle and of the shorthand:public class S { public static ResourceBundle myResources = ResourceBundle.getBundle("domain-name"); public static String i18n(String s) { return myResources.getString(s); } }
and the shorthand is used like this:
System.out.println(S.i18n("Operation completed."));
Which of the three idioms you choose, will depend on whether your project requires portability to Java versions prior to Java 1.5 and, if so, whether copying two lines of codes into every class is more acceptable in your project than a class with a single-letter name.
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