java.util: abstract public class: ResourceBundle

java.util
abstract public class: ResourceBundle [javadoc | source]

java.lang.Object
   java.util.ResourceBundle

Direct Known Subclasses:
DuplicatedPropertiesResourceBundle, PropertyResourceBundle, ListResourceBundle

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 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 {
    protected Object[][] getContents() {
        return new Object[][] {
            // LOCALIZE THE SECOND STRING OF EACH ARRAY (e.g., "OK")
            {"OkKey", "OK"},
            {"CancelKey", "Cancel"},
            // END OF MATERIAL TO LOCALIZE
       };
    }
}

Keys are always Strings. In this example, the keys are "OkKey" and "CancelKey". In the above example, the values are also Strings--"OK" and "Cancel"--but they don't have to be. The values can be any type of object.

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"));

The getter methods all require the key as an argument and return the object if found. If the object is not found, the getter method throws a MissingResourceException.

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 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().

ResourceBundle.Control

The ResourceBundle.Control class provides information necessary to perform the bundle loading process by the getBundle factory methods that take a ResourceBundle.Control instance. You can implement your own subclass in order to enable non-standard resource bundle formats, change the search strategy, or define caching parameters. Refer to the descriptions of the class and the getBundle factory method for details.

Cache Management

Resource bundle instances created by the getBundle factory methods are cached by default, and the factory methods return the same resource bundle instance multiple times if it has been cached. getBundle clients may clear the cache, manage the lifetime of cached resource bundle instances using time-to-live values, or specify not to cache resource bundle instances. Refer to the descriptions of the {@linkplain #getBundle(String, Locale, ClassLoader, Control) getBundle factory method}, clearCache , Locale) ResourceBundle.Control.getTimeToLive , and ResourceBundle.Control.needsReload for details.

Example

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 Map). 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).

// 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;
    }

    public Enumeration<String> getKeys() {
        return Collections.enumeration(keySet());
    }

    // Overrides handleKeySet() so that the getKeys() implementation
    // can rely on the keySet() value.
    protected Set<String> handleKeySet() {
        return new HashSet<String>(Arrays.asList("okKey", "cancelKey"));
    }
}

// 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;
    }

    protected Set<String> handleKeySet() {
        return new HashSet<String>(Arrays.asList("cancelKey"));
    }
}

You do not have to restrict yourself to using a single family of ResourceBundles. For example, you could have a set of bundles for exception messages, ExceptionResources (ExceptionResources_fr, ExceptionResources_de, ...), and one for widgets, WidgetResource (WidgetResources_fr, WidgetResources_de, ...); breaking up the resources however you like.

Also see:

ListResourceBundle

PropertyResourceBundle

MissingResourceException

since: JDK1.1 -

Nested Class Summary:

public static class

Nested Class Summary:
public static class	ResourceBundle.Control	`ResourceBundle.Control` defines a set of callback methods that are invoked by the {@link ResourceBundle#getBundle(String, Locale, ClassLoader, Control) ResourceBundle.getBundle} factory methods during the bundle loading process. In other words, a `ResourceBundle.Control` collaborates with the factory methods for loading resource bundles. The default implementation of the callback methods provides the information necessary for the factory methods to perform the default behavior. In addition to the callback methods, the {@link #toBundleName(String, Locale) toBundleName} and {@link #toResourceName(String, String) toResourceName} methods are defined primarily for convenience in implementing the callback methods. However, the `toBundleName` method could be overridden to provide different conventions in the organization and packaging of localized resources. The `toResourceName` method is `final` to avoid use of wrong resource and class name separators. Two factory methods, {@link #getControl(List)} and {@link #getNoFallbackControl(List)}, provide `ResourceBundle.Control` instances that implement common variations of the default bundle loading process. The formats returned by the {@link Control#getFormats(String) getFormats} method and candidate locales returned by the {@link ResourceBundle.Control#getCandidateLocales(String, Locale) getCandidateLocales} method must be consistent in all `ResourceBundle.getBundle` invocations for the same base bundle. Otherwise, the `ResourceBundle.getBundle` methods may return unintended bundles. For example, if only `"java.class"` is returned by the `getFormats` method for the first call to `ResourceBundle.getBundle` and only `"java.properties"` for the second call, then the second call will return the class-based one that has been cached during the first call. A `ResourceBundle.Control` instance must be thread-safe if it's simultaneously used by multiple threads. `ResourceBundle.getBundle` does not synchronize to call the `ResourceBundle.Control` methods. The default implementations of the methods are thread-safe. Applications can specify `ResourceBundle.Control` instances returned by the `getControl` factory methods or created from a subclass of `ResourceBundle.Control` to customize the bundle loading process. The following are examples of changing the default bundle loading process. Example 1 The following code lets `ResourceBundle.getBundle` look up only properties-based resources. import java.util.; import static java.util.ResourceBundle.Control.; ... ResourceBundle bundle = ResourceBundle.getBundle("MyResources", new Locale("fr", "CH"), ResourceBundle.Control.getControl(FORMAT_PROPERTIES)); Given the resource bundles in the example in the `ResourceBundle.getBundle` description, this `ResourceBundle.getBundle` call loads `MyResources_fr_CH.properties` whose parent is `MyResources_fr.properties` whose parent is `MyResources.properties`. (`MyResources_fr_CH.properties` is not hidden, but `MyResources_fr_CH.class` is.) Example 2 The following is an example of loading XML-based bundles using {@link Properties#loadFromXML(java.io.InputStream) Properties.loadFromXML}. ResourceBundle rb = ResourceBundle.getBundle("Messages", new ResourceBundle.Control() { public List<String> getFormats(String baseName) { if (baseName == null) throw new NullPointerException(); return Arrays.asList("xml"); } public ResourceBundle newBundle(String baseName, Locale locale, String format, ClassLoader loader, boolean reload) throws IllegalAccessException, InstantiationException, IOException { if (baseName == null \|\| locale == null \|\| format == null \|\| loader == null) throw new NullPointerException(); ResourceBundle bundle = null; if (format.equals("xml")) { String bundleName = toBundleName(baseName, locale); String resourceName = toResourceName(bundleName, format); InputStream stream = null; if (reload) { URL url = loader.getResource(resourceName); if (url != null) { URLConnection connection = url.openConnection(); if (connection != null) { // Disable caches to get fresh data for // reloading. connection.setUseCaches(false); stream = connection.getInputStream(); } } } else { stream = loader.getResourceAsStream(resourceName); } if (stream != null) { BufferedInputStream bis = new BufferedInputStream(stream); bundle = new XMLResourceBundle(bis); bis.close(); } } return bundle; } }); ... private static class XMLResourceBundle extends ResourceBundle { private Properties props; XMLResourceBundle(InputStream stream) throws IOException { props = new Properties(); props.loadFromXML(stream); } protected Object handleGetObject(String key) { return props.getProperty(key); } public Enumeration<String> getKeys() { ... } }

ResourceBundle.Control

ResourceBundle.Control defines a set of callback methods that are invoked by the {@link ResourceBundle#getBundle(String, Locale, ClassLoader, Control) ResourceBundle.getBundle} factory methods during the bundle loading process. In other words, a ResourceBundle.Control collaborates with the factory methods for loading resource bundles. The default implementation of the callback methods provides the information necessary for the factory methods to perform the default behavior.

In addition to the callback methods, the {@link #toBundleName(String, Locale) toBundleName} and {@link #toResourceName(String, String) toResourceName} methods are defined primarily for convenience in implementing the callback methods. However, the toBundleName method could be overridden to provide different conventions in the organization and packaging of localized resources. The toResourceName method is final to avoid use of wrong resource and class name separators.

Two factory methods, {@link #getControl(List)} and {@link #getNoFallbackControl(List)}, provide ResourceBundle.Control instances that implement common variations of the default bundle loading process.

The formats returned by the {@link Control#getFormats(String) getFormats} method and candidate locales returned by the {@link ResourceBundle.Control#getCandidateLocales(String, Locale) getCandidateLocales} method must be consistent in all ResourceBundle.getBundle invocations for the same base bundle. Otherwise, the ResourceBundle.getBundle methods may return unintended bundles. For example, if only "java.class" is returned by the getFormats method for the first call to ResourceBundle.getBundle and only "java.properties" for the second call, then the second call will return the class-based one that has been cached during the first call.

A ResourceBundle.Control instance must be thread-safe if it's simultaneously used by multiple threads. ResourceBundle.getBundle does not synchronize to call the ResourceBundle.Control methods. The default implementations of the methods are thread-safe.

Applications can specify ResourceBundle.Control instances returned by the getControl factory methods or created from a subclass of ResourceBundle.Control to customize the bundle loading process. The following are examples of changing the default bundle loading process.

Example 1

The following code lets ResourceBundle.getBundle look up only properties-based resources.

import java.util.*;
import static java.util.ResourceBundle.Control.*;
...
ResourceBundle bundle =
  ResourceBundle.getBundle("MyResources", new Locale("fr", "CH"),
                           ResourceBundle.Control.getControl(FORMAT_PROPERTIES));

Given the resource bundles in the example in the ResourceBundle.getBundle description, this ResourceBundle.getBundle call loads MyResources_fr_CH.properties whose parent is MyResources_fr.properties whose parent is MyResources.properties. (MyResources_fr_CH.properties is not hidden, but MyResources_fr_CH.class is.)

Example 2

The following is an example of loading XML-based bundles using {@link Properties#loadFromXML(java.io.InputStream) Properties.loadFromXML}.

ResourceBundle rb = ResourceBundle.getBundle("Messages",
    new ResourceBundle.Control() {
        public List<String> getFormats(String baseName) {
            if (baseName == null)
                throw new NullPointerException();
            return Arrays.asList("xml");
        }
        public ResourceBundle newBundle(String baseName,
                                        Locale locale,
                                        String format,
                                        ClassLoader loader,
                                        boolean reload)
                         throws IllegalAccessException,
                                InstantiationException,
                                IOException {
            if (baseName == null || locale == null
                  || format == null || loader == null)
                throw new NullPointerException();
            ResourceBundle bundle = null;
            if (format.equals("xml")) {
                String bundleName = toBundleName(baseName, locale);
                String resourceName = toResourceName(bundleName, format);
                InputStream stream = null;
                if (reload) {
                    URL url = loader.getResource(resourceName);
                    if (url != null) {
                        URLConnection connection = url.openConnection();
                        if (connection != null) {
                            // Disable caches to get fresh data for
                            // reloading.
                            connection.setUseCaches(false);
                            stream = connection.getInputStream();
                        }
                    }
                } else {
                    stream = loader.getResourceAsStream(resourceName);
                }
                if (stream != null) {
                    BufferedInputStream bis = new BufferedInputStream(stream);
                    bundle = new XMLResourceBundle(bis);
                    bis.close();
                }
            }
            return bundle;
        }
    });

...

private static class XMLResourceBundle extends ResourceBundle {
    private Properties props;
    XMLResourceBundle(InputStream stream) throws IOException {
        props = new Properties();
        props.loadFromXML(stream);
    }
    protected Object handleGetObject(String key) {
        return props.getProperty(key);
    }
    public Enumeration<String> getKeys() {
        ...
    }
}

Field Summary
protected ResourceBundle	parent	The parent bundle of this bundle. The parent bundle is searched by getObject when this bundle does not contain a particular resource.

Constructor:
public ResourceBundle() { } Sole constructor. (For invocation by subclass constructors, typically implicit.)

Constructor:

 public ResourceBundle() {

}

Sole constructor. (For invocation by subclass constructors, typically implicit.)

Method from java.util.ResourceBundle Summary:
clearCache, clearCache, containsKey, getBundle, getBundle, getBundle, getBundle, getBundle, getBundle, getKeys, getLocale, getObject, getString, getStringArray, handleGetObject, handleKeySet, keySet, setParent

Methods from java.lang.Object:
clone, equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait

Method from java.util.ResourceBundle Detail:

 public static final  void clearCache() {
        clearCache(getLoader());
}

Removes all resource bundles from the cache that have been loaded using the caller's class loader.

 public static final  void clearCache(ClassLoader loader) {
        if (loader == null) {
            throw new NullPointerException();
        }
        Set< CacheKey > set = cacheList.keySet();
        for (CacheKey key : set) {
            if (key.getLoader() == loader) {
                set.remove(key);
            }
        }
}

Removes all resource bundles from the cache that have been loaded using the given class loader.

 public boolean containsKey(String key) {
        if (key == null) {
            throw new NullPointerException();
        }
        for (ResourceBundle rb = this; rb != null; rb = rb.parent) {
            if (rb.handleKeySet().contains(key)) {
                return true;
            }
        }
        return false;
}

key

ResourceBundle

 public static final ResourceBundle getBundle(String baseName) {
        return getBundleImpl(baseName, Locale.getDefault(),
                             /* must determine loader here, else we break stack invariant */
                             getLoader(),
                             Control.INSTANCE);
}

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

getClassLoader()

ResourceBundle

getBundle

 public static final ResourceBundle getBundle(String baseName,
    Control control) {
        return getBundleImpl(baseName, Locale.getDefault(),
                             /* must determine loader here, else we break stack invariant */
                             getLoader(),
                             control);
}

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

getClassLoader()

ResourceBundle

getBundle

ResourceBundle.Control

 public static final ResourceBundle getBundle(String baseName,
    Locale locale) {
        return getBundleImpl(baseName, locale,
                             /* must determine loader here, else we break stack invariant */
                             getLoader(),
                             Control.INSTANCE);
}

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

getClassLoader()

ResourceBundle

getBundle

 public static final ResourceBundle getBundle(String baseName,
    Locale targetLocale,
    Control control) {
        return getBundleImpl(baseName, targetLocale,
                             /* must determine loader here, else we break stack invariant */
                             getLoader(),
                             control);
}

getBundle(baseName, targetLocale, this.getClass().getClassLoader(),
          control),

getClassLoader()

ResourceBundle

getBundle

ResourceBundle.Control

 public static ResourceBundle getBundle(String baseName,
    Locale locale,
    ClassLoader loader) {
        if (loader == null) {
            throw new NullPointerException();
        }
        return getBundleImpl(baseName, locale, loader, Control.INSTANCE);
}

This method behaves the same as calling #getBundle(String, Locale, ClassLoader, Control) passing a default instance of Control . The following describes this behavior.

getBundle uses the base name, the specified locale, and the default locale (obtained from Locale.getDefault ) to generate a sequence of candidate bundle names. If the specified locale's language, script, country, and variant are all empty strings, then the base name is the only candidate bundle name. Otherwise, a list of candidate locales is generated from the attribute values of the specified locale (language, script, country and variant) and appended to the base name. Typically, this will look like the following:

    baseName + "_" + language + "_" + script + "_" + country + "_" + variant
    baseName + "_" + language + "_" + script + "_" + country
    baseName + "_" + language + "_" + script
    baseName + "_" + language + "_" + country + "_" + variant
    baseName + "_" + language + "_" + country
    baseName + "_" + language

Candidate bundle names where the final component is an empty string are omitted, along with the underscore. For example, if country is an empty string, the second and the fifth candidate bundle names above would be omitted. Also, if script is an empty string, the candidate names including script are omitted. For example, a locale with language "de" and variant "JAVA" will produce candidate names with base name "MyResource" below.

    MyResource_de__JAVA
    MyResource_de

MyResource_en_Latn_US_WINDOWS_VISTA
MyResource_en_Latn_US_WINDOWS
MyResource_en_Latn_US
MyResource_en_Latn
MyResource_en_US_WINDOWS_VISTA
MyResource_en_US_WINDOWS
MyResource_en_US
MyResource_en

Note: For some Locales, the list of candidate bundle names contains extra names, or the order of bundle names is slightly modified. See the description of the default implementation of Locale) getCandidateLocales for details.

getBundle then iterates over the candidate bundle names to find the first one for which it can instantiate an actual resource bundle. It uses the default controls' getFormats method, which generates two bundle names for each generated name, the first a class name and the second a properties file name. For each candidate bundle name, it attempts to create a resource bundle:

First, it attempts to load a class using the generated class 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 using the generated properties file name. 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 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 PropertyResourceBundle instance from its contents. If successful, this instance becomes the result resource bundle.

This continues until a result resource bundle is instantiated or the list of candidate bundle names is exhausted. If no matching resource bundle is found, the default control's getFallbackLocale method is called, which returns the current default locale. A new sequence of candidate locale names is generated using this locale and and searched again, as above.

If still no result bundle is found, the base name alone is looked up. If this still fails, a MissingResourceException is thrown.

Once a result resource bundle has been found, its parent chain is instantiated. If the result bundle already has a parent (perhaps because it was returned from a cache) the chain is complete.

Otherwise, getBundle examines the remainder of the candidate locale list that was used during the pass that generated the result resource bundle. (As before, candidate bundle names where the final component is an empty string are omitted.) When it comes to the end of the candidate list, it tries the plain bundle name. With each of the candidate bundle names it attempts to instantiate a resource bundle (first looking for a class and then a properties file, as described above).

Whenever it succeeds, it calls the previously instantiated resource bundle's setParent method with the new resource bundle. This continues until the list of names is exhausted or the current bundle already has a non-null parent.

Once the parent chain is complete, the bundle is returned.

Note: getBundle caches instantiated resource bundles and might return the same resource bundle instance multiple times.

Note:The baseName argument should be a fully qualified class name. However, for compatibility with earlier versions, Sun's Java SE 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.properties
    MyResources_fr.properties
    MyResources_fr_CH.class
    MyResources_fr_CH.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 locale arguments below will instantiate resource bundles as follows:

Locale("fr", "CH") MyResources_fr_CH.class, parent MyResources_fr.properties, parent MyResources.class

Locale("fr", "FR") MyResources_fr.properties, parent MyResources.class

Locale("de", "DE") MyResources_en.properties, parent MyResources.class

Locale("en", "US") MyResources_en.properties, parent MyResources.class

Locale("es", "ES") MyResources_es_ES.class, parent MyResources.class

The file MyResources_fr_CH.properties is never used because it is hidden by the MyResources_fr_CH.class. Likewise, MyResources.properties is also hidden by MyResources.class.

 public static ResourceBundle getBundle(String baseName,
    Locale targetLocale,
    ClassLoader loader,
    Control control) {
        if (loader == null || control == null) {
            throw new NullPointerException();
        }
        return getBundleImpl(baseName, targetLocale, loader, control);
}

getBundle

control

This factory method looks up the resource bundle in the cache for the specified baseName, targetLocale and loader. If the requested resource bundle instance is found in the cache and the time-to-live periods of the instance and all of its parent instances have not expired, the instance is returned to the caller. Otherwise, this factory method proceeds with the loading process below.
The control.getFormats method is called to get resource bundle formats to produce bundle or resource names. The strings "java.class" and "java.properties" designate class-based and {@linkplain PropertyResourceBundle property}-based resource bundles, respectively. Other strings starting with "java." are reserved for future extensions and must not be used for application-defined formats. Other strings designate application-defined formats.
The control.getCandidateLocales method is called with the target locale to get a list of candidate Locales for which resource bundles are searched.

The control.newBundle method is called to instantiate a ResourceBundle for the base bundle name, a candidate locale, and a format. (Refer to the note on the cache lookup below.) This step is iterated over all combinations of the candidate locales and formats until the newBundle method returns a ResourceBundle instance or the iteration has used up all the combinations. For example, if the candidate locales are Locale("de", "DE"), Locale("de") and Locale("") and the formats are "java.class" and "java.properties", then the following is the sequence of locale-format combinations to be used to call control.newBundle.

Locale	format
Locale("de", "DE")	java.class
Locale("de", "DE")	java.properties
Locale("de")	java.class
Locale("de")	java.properties
Locale("")	java.class
Locale("")	java.properties

If the previous step has found no resource bundle, proceed to Step 6. If a bundle has been found that is a base bundle (a bundle for Locale("")), and the candidate locale list only contained Locale(""), return the bundle to the caller. If a bundle has been found that is a base bundle, but the candidate locale list contained locales other than Locale(""), put the bundle on hold and proceed to Step 6. If a bundle has been found that is not a base bundle, proceed to Step 7.
The control.getFallbackLocale method is called to get a fallback locale (alternative to the current target locale) to try further finding a resource bundle. If the method returns a non-null locale, it becomes the next target locale and the loading process starts over from Step 3. Otherwise, if a base bundle was found and put on hold in a previous Step 5, it is returned to the caller now. Otherwise, a MissingResourceException is thrown.
At this point, we have found a resource bundle that's not the base bundle. If this bundle set its parent during its instantiation, it is returned to the caller. Otherwise, its parent chain is instantiated based on the list of candidate locales from which it was found. Finally, the bundle is returned to the caller.

During the resource bundle loading process above, this factory method looks up the cache before calling the Locale, String, ClassLoader, boolean) control.newBundle method. If the time-to-live period of the resource bundle found in the cache has expired, the factory method calls the control.needsReload method to determine whether the resource bundle needs to be reloaded. If reloading is required, the factory method calls control.newBundle to reload the resource bundle. If control.newBundle returns null, the factory method puts a dummy resource bundle in the cache as a mark of nonexistent resource bundles in order to avoid lookup overhead for subsequent requests. Such dummy resource bundles are under the same expiration control as specified by control.

All resource bundles loaded are cached by default. Refer to control.getTimeToLive for details.

The following is an example of the bundle loading process with the default ResourceBundle.Control implementation.

Conditions:

Base bundle name: foo.bar.Messages
Requested Locale: Locale#ITALY
Default Locale: Locale#FRENCH
Available resource bundles: foo/bar/Messages_fr.properties and foo/bar/Messages.properties

First, getBundle tries loading a resource bundle in the following sequence.

class foo.bar.Messages_it_IT
file foo/bar/Messages_it_IT.properties
class foo.bar.Messages_it
file foo/bar/Messages_it.properties
class foo.bar.Messages
file foo/bar/Messages.properties

At this point, getBundle finds foo/bar/Messages.properties, which is put on hold because it's the base bundle. getBundle calls Locale) Locale.ITALY) which returns Locale.FRENCH. Next, getBundle tries loading a bundle in the following sequence.

class foo.bar.Messages_fr
file foo/bar/Messages_fr.properties
class foo.bar.Messages
file foo/bar/Messages.properties

getBundle finds foo/bar/Messages_fr.properties and creates a ResourceBundle instance. Then, getBundle sets up its parent chain from the list of the candiate locales. Only foo/bar/Messages.properties is found in the list and getBundle creates a ResourceBundle instance that becomes the parent of the instance for foo/bar/Messages_fr.properties.

 abstract public Enumeration<String> getKeys()Returns an enumeration of the keys.

 public Locale getLocale() {
        return locale;
}

Returns the locale of this resource bundle. This method can be used after a call to getBundle() to determine whether the resource bundle returned really corresponds to the requested locale or is a fallback.

 public final Object getObject(String key) {
        Object obj = handleGetObject(key);
        if (obj == null) {
            if (parent != null) {
                obj = parent.getObject(key);
            }
            if (obj == null)
                throw new MissingResourceException("Can't find resource for bundle "
                                                   +this.getClass().getName()
                                                   +", key "+key,
                                                   this.getClass().getName(),
                                                   key);
        }
        return obj;
}

handleGetObject

getObject

 public final String getString(String key) {
        return (String) getObject(key);
}

(String) getObject (key).

 public final String[] getStringArray(String key) {
        return (String[]) getObject(key);
}

(String[]) getObject (key).

 abstract protected Object handleGetObject(String key)Gets an object for the given key from this resource bundle.
Returns null if this resource bundle does not contain an
object for the given key.

 protected Set<String> handleKeySet() {
        if (keySet == null) {
            synchronized (this) {
                if (keySet == null) {
                    Set< String > keys = new HashSet<  >();
                    Enumeration< String > enumKeys = getKeys();
                    while (enumKeys.hasMoreElements()) {
                        String key = enumKeys.nextElement();
                        if (handleGetObject(key) != null) {
                            keys.add(key);
                        }
                    }
                    keySet = keys;
                }
            }
        }
        return keySet;
}

Set

only

ResourceBundle

The default implementation returns a Set of the keys returned by the getKeys method except for the ones for which the handleGetObject method returns null. Once the Set has been created, the value is kept in this ResourceBundle in order to avoid producing the same Set in subsequent calls. Subclasses can override this method for faster handling.

 public Set<String> keySet() {
        Set< String > keys = new HashSet<  >();
        for (ResourceBundle rb = this; rb != null; rb = rb.parent) {
            keys.addAll(rb.handleKeySet());
        }
        return keys;
}

Set

ResourceBundle

 protected  void setParent(ResourceBundle parent) {
        assert parent != NONEXISTENT_BUNDLE;
        this.parent = parent;
}

getObject