java.util.ResourceBundle Maven / Gradle / Ivy

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This work corresponds to the API signatures of JSR 219: Foundation Profile 1.1. In the event of a discrepency between this work and the JSR 219 specification, which is available at http://www.jcp.org/en/jsr/detail?id=219, the latter takes precedence. */ package java.util; import java.io.InputStream; import java.lang.ref.Reference; import java.lang.ref.ReferenceQueue; import java.lang.ref.WeakReference; /** * Resource bundles contain locale-specific objects. * When your program needs a locale-specific resource, * a String for example, your program can load it * from the resource bundle that is appropriate for the * current user's locale. In this way, you can write * program code that is largely independent of the user's * locale isolating most, if not all, of the locale-specific * information in resource bundles. * *

* This allows you to write programs that can: *

*
• be easily localized, or translated, into different languages *
• handle multiple locales at once *
• be easily modified later to support even more locales *

* Resource bundles belong to families whose members share a common base * name, but whose names also have additional components that identify * their locales. For example, the base name of a family of resource * bundles might be "MyResources". The family should have a default * resource bundle which simply has the same name as its family - * "MyResources" - and will be used as the bundle of last resort if a * specific locale is not supported. The family can then provide as * many locale-specific members as needed, for example a German one * named "MyResources_de". * *

* Each resource bundle in a family contains the same items, but the items have * been translated for the locale represented by that resource bundle. * For example, both "MyResources" and "MyResources_de" may have a * String that's used on a button for canceling operations. * In "MyResources" the String may contain "Cancel" and in * "MyResources_de" it may contain "Abbrechen". * *

* If there are different resources for different countries, you * can make specializations: for example, "MyResources_de_CH" contains objects for * the German language (de) in Switzerland (CH). If you want to only * modify some of the resources * in the specialization, you can do so. * *

* When your program needs a locale-specific object, it loads * the ResourceBundle class using the * {@link #getBundle(java.lang.String, java.util.Locale) getBundle} * method: *

*

 * ResourceBundle myResources =
 *      ResourceBundle.getBundle("MyResources", currentLocale);
 * 

*

* Resource bundles contain key/value pairs. The keys uniquely * identify a locale-specific object in the bundle. Here's an * example of a ListResourceBundle that contains * two key/value pairs: *

*

 * public class MyResources extends ListResourceBundle {
 *      public Object[][] getContents() {
 *              return contents;
 *      }
 *      static final Object[][] contents = {
 *      // LOCALIZE THIS
 *              {"OkKey", "OK"},
 *              {"CancelKey", "Cancel"},
 *      // END OF MATERIAL TO LOCALIZE
 *      };
 * }
 * 

*

* You retrieve an object from resource bundle using the appropriate * getter method. Because "OkKey" and "CancelKey" * are both strings, you would use getString to retrieve them: *

*

 * button1 = new Button(myResources.getString("OkKey"));
 * button2 = new Button(myResources.getString("CancelKey"));
 * 

*

* Besides getString, ResourceBundle also provides * a method for getting string arrays, getStringArray, * as well as a generic getObject method for any other * type of object. When using getObject, you'll * have to cast the result to the appropriate type. For example: *

*

 * int[] myIntegers = (int[]) myResources.getObject("intList");
 * 

*

* The Java 2 platform provides two subclasses of ResourceBundle, * ListResourceBundle and PropertyResourceBundle, * that provide a fairly simple way to create resources. * As you saw briefly in a previous example, ListResourceBundle * manages its resource as a List of key/value pairs. * PropertyResourceBundle uses a properties file to manage * its resources. * *

* If ListResourceBundle or PropertyResourceBundle * do not suit your needs, you can write your own ResourceBundle * subclass. Your subclasses must override two methods: handleGetObject * and getKeys(). * *

* The following is a very simple example of a ResourceBundle * subclass, MyResources, that manages two resources (for a larger number of * resources you would probably use a Hashtable). * Notice that you don't need to supply a value if * a "parent-level" ResourceBundle handles the same * key with the same value (as for the okKey below). *

Example: *

*

 * // default (English language, United States)
 * public class MyResources extends ResourceBundle {
 *     public Object handleGetObject(String key) {
 *         if (key.equals("okKey")) return "Ok";
 *         if (key.equals("cancelKey")) return "Cancel";
 *         return null;
 *     }
 * }
 *
 * // German language
 * public class MyResources_de extends MyResources {
 *     public Object handleGetObject(String key) {
 *         // don't need okKey, since parent level handles it.
 *         if (key.equals("cancelKey")) return "Abbrechen";
 *         return null;
 *     }
 * }
 * 

*

* (String) {@link #getObject(java.lang.String) getObject}(key). *

* (String[]) {@link #getObject(java.lang.String) getObject}(key). *

* getBundle(baseName, Locale.getDefault(), this.getClass().getClassLoader()), *

* getBundle(baseName, locale, this.getClass().getClassLoader()), *

* Conceptually, getBundle uses the following strategy for locating and instantiating * resource bundles: *

* getBundle uses the base name, the specified locale, and the default * locale (obtained from {@link java.util.Locale#getDefault() Locale.getDefault}) * to generate a sequence of candidate bundle names. * If the specified locale's language, country, and variant are all empty * strings, then the base name is the only candidate bundle name. * Otherwise, the following sequence is generated from the attribute * values of the specified locale (language1, country1, and variant1) * and of the default locale (language2, country2, and variant2): *

*
• baseName + "_" + language1 + "_" + country1 + "_" + variant1 *
• baseName + "_" + language1 + "_" + country1 *
• baseName + "_" + language1 *
• baseName + "_" + language2 + "_" + country2 + "_" + variant2 *
• baseName + "_" + language2 + "_" + country2 *
• baseName + "_" + language2 *
• baseName *

* Candidate bundle names where the final component is an empty string are omitted. * For example, if country1 is an empty string, the second candidate bundle name is omitted. * *

* getBundle then iterates over the candidate bundle names to find the first * one for which it can instantiate an actual resource bundle. For each candidate * bundle name, it attempts to create a resource bundle: *

*
• * First, it attempts to load a class using the candidate bundle name. * If such a class can be found and loaded using the specified class loader, is assignment * compatible with ResourceBundle, is accessible from ResourceBundle, and can be instantiated, * getBundle creates a new instance of this class and uses it as the result * resource bundle. *
• * Otherwise, getBundle attempts to locate a property resource file. * It generates a path name from the candidate bundle name by replacing all "." characters * with "/" and appending the string ".properties". * It attempts to find a "resource" with this name using * {@link java.lang.ClassLoader#getResource(java.lang.String) ClassLoader.getResource}. * (Note that a "resource" in the sense of getResource has nothing to do with * the contents of a resource bundle, it is just a container of data, such as a file.) * If it finds a "resource", it attempts to create a new * {@link PropertyResourceBundle} instance from its contents. * If successful, this instance becomes the result resource bundle. *

* If no result resource bundle has been found, a MissingResourceException * is thrown. * *

* Once a result resource bundle has been found, its parent chain is instantiated. * getBundle iterates over the candidate bundle names that can be * obtained by successively removing variant, country, and language * (each time with the preceding "_") from the bundle name of the result resource bundle. * As above, candidate bundle names where the final component is an empty string are omitted. * With each of the candidate bundle names it attempts to instantiate a resource bundle, as * described above. * Whenever it succeeds, it calls the previously instantiated resource * bundle's {@link #setParent(java.util.ResourceBundle) setParent} method * with the new resource bundle, unless the previously instantiated resource * bundle already has a non-null parent. * *

* Implementations of getBundle may cache instantiated resource bundles * and return the same resource bundle instance multiple times. They may also * vary the sequence in which resource bundles are instantiated as long as the * selection of the result resource bundle and its parent chain are compatible with * the description above. * *

* The baseName argument should be a fully qualified class name. However, for * compatibility with earlier versions, Sun's Java 2 runtime environments do not verify this, * and so it is possible to access PropertyResourceBundles by specifying a * path name (using "/") instead of a fully qualified class name (using "."). * *

* Example: The following class and property files are provided: * MyResources.class, MyResources_fr_CH.properties, MyResources_fr_CH.class, * MyResources_fr.properties, MyResources_en.properties, MyResources_es_ES.class. * The contents of all files are valid (that is, public non-abstract subclasses of ResourceBundle for * the ".class" files, syntactically correct ".properties" files). * The default locale is Locale("en", "GB"). *

* Calling getBundle with the shown locale argument values instantiates * resource bundles from the following sources: *

*
• Locale("fr", "CH"): result MyResources_fr_CH.class, parent MyResources_fr.properties, parent MyResources.class *
• Locale("fr", "FR"): result MyResources_fr.properties, parent MyResources.class *
• Locale("de", "DE"): result MyResources_en.properties, parent MyResources.class *
• Locale("en", "US"): result MyResources_en.properties, parent MyResources.class *
• Locale("es", "ES"): result MyResources_es_ES.class, parent MyResources.class *