Class ResourceBundle.Control

Enclosing class:
ResourceBundle
public static class ResourceBundle.Control
extends Object

ResourceBundle.Control defines a set of callback methods that are invoked by the 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.

ResourceBundle.Control is designed for an application deployed in an unnamed module, for example to support resource bundles in non-standard formats or package localized resources in a non-traditional convention. ResourceBundleProvider is the replacement for ResourceBundle.Control when migrating to modules. UnsupportedOperationException will be thrown when a factory method that takes the ResourceBundle.Control parameter is called.

In addition to the callback methods, the toBundleName and 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, getControl(List) and getNoFallbackControl(List), provide ResourceBundle.Control instances that implement common variations of the default bundle loading process.

The formats returned by the getFormats method and candidate locales returned by the 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 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() {
         ...
     }
 }
API Note:
ResourceBundle.Control is not supported in named modules. If the ResourceBundle.getBundle method with a ResourceBundle.Control is called in a named module, the method will throw an UnsupportedOperationException. Any service providers of ResourceBundleControlProvider are ignored in named modules.
Since:
1.6
See Also:
ResourceBundleProvider

Field Summary

Fields
Modifier and Type Field Description
static List<String> FORMAT_CLASS

The class-only format List containing "java.class".
static List<String> FORMAT_DEFAULT

The default format List, which contains the strings "java.class" and "java.properties", in this order.
static List<String> FORMAT_PROPERTIES

The properties-only format List containing "java.properties".
static long TTL_DONT_CACHE

The time-to-live constant for not caching loaded resource bundle instances.
static long TTL_NO_EXPIRATION_CONTROL

The time-to-live constant for disabling the expiration control for loaded resource bundle instances in the cache.

Constructor Summary

Constructors
Modifier Constructor Description
protected Control()

Sole constructor.

Method Summary

All Methods Static Methods Instance Methods Concrete Methods
Modifier and Type Method Description
List<Locale> getCandidateLocales​(String baseName, Locale locale)

Returns a List of Locales as candidate locales for baseName and locale.
static ResourceBundle.Control getControl​(List<String> formats)

Returns a ResourceBundle.Control in which the getFormats method returns the specified formats.
Locale getFallbackLocale​(String baseName, Locale locale)

Returns a Locale to be used as a fallback locale for further resource bundle searches by the ResourceBundle.getBundle factory method.
List<String> getFormats​(String baseName)

Returns a List of Strings containing formats to be used to load resource bundles for the given baseName.
static ResourceBundle.Control getNoFallbackControl​(List<String> formats)

Returns a ResourceBundle.Control in which the getFormats method returns the specified formats and the getFallbackLocale method returns null.
long getTimeToLive​(String baseName, Locale locale)

Returns the time-to-live (TTL) value for resource bundles that are loaded under this ResourceBundle.Control.
boolean needsReload​(String baseName, Locale locale, String format, ClassLoader loader, ResourceBundle bundle, long loadTime)

Determines if the expired bundle in the cache needs to be reloaded based on the loading time given by loadTime or some other criteria.
ResourceBundle newBundle​(String baseName, Locale locale, String format, ClassLoader loader, boolean reload)

Instantiates a resource bundle for the given bundle name of the given format and locale, using the given class loader if necessary.
String toBundleName​(String baseName, Locale locale)

Converts the given baseName and locale to the bundle name.
String toResourceName​(String bundleName, String suffix)

Converts the given bundleName to the form required by the ClassLoader.getResource method by replacing all occurrences of '.' in bundleName with '/' and appending a '.' and the given file suffix.

Methods declared in class java.lang.Object

clone, equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait

Field Detail

FORMAT_DEFAULT

public static final List<String> FORMAT_DEFAULT

The default format List, which contains the strings "java.class" and "java.properties", in this order. This List is unmodifiable.

See Also:
getFormats(String)

FORMAT_CLASS

public static final List<String> FORMAT_CLASS

The class-only format List containing "java.class". This List is unmodifiable.

See Also:
getFormats(String)

FORMAT_PROPERTIES

public static final List<String> FORMAT_PROPERTIES

The properties-only format List containing "java.properties". This List is unmodifiable.

See Also:
getFormats(String)

TTL_DONT_CACHE

public static final long TTL_DONT_CACHE

The time-to-live constant for not caching loaded resource bundle instances.

See Also:
getTimeToLive(String, Locale), Constant Field Values

TTL_NO_EXPIRATION_CONTROL

public static final long TTL_NO_EXPIRATION_CONTROL

The time-to-live constant for disabling the expiration control for loaded resource bundle instances in the cache.

See Also:
getTimeToLive(String, Locale), Constant Field Values

Constructor Detail

Control

protected Control()

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

Method Detail

getControl

public static final ResourceBundle.Control getControl​(List<String> formats)

Returns a ResourceBundle.Control in which the getFormats method returns the specified formats. The formats must be equal to one of FORMAT_PROPERTIES, FORMAT_CLASS or FORMAT_DEFAULT. ResourceBundle.Control instances returned by this method are singletons and thread-safe.

Specifying FORMAT_DEFAULT is equivalent to instantiating the ResourceBundle.Control class, except that this method returns a singleton.

Parameters:
formats - the formats to be returned by the ResourceBundle.Control.getFormats method
Returns:
a ResourceBundle.Control supporting the specified formats
Throws:
NullPointerException - if formats is null
IllegalArgumentException - if formats is unknown

getNoFallbackControl

public static final ResourceBundle.Control getNoFallbackControl​(List<String> formats)

Returns a ResourceBundle.Control in which the getFormats method returns the specified formats and the getFallbackLocale method returns null. The formats must be equal to one of FORMAT_PROPERTIES, FORMAT_CLASS or FORMAT_DEFAULT. ResourceBundle.Control instances returned by this method are singletons and thread-safe.

Parameters:
formats - the formats to be returned by the ResourceBundle.Control.getFormats method
Returns:
a ResourceBundle.Control supporting the specified formats with no fallback Locale support
Throws:
NullPointerException - if formats is null
IllegalArgumentException - if formats is unknown

getFormats

public List<String> getFormats​(String baseName)

Returns a List of Strings containing formats to be used to load resource bundles for the given baseName. The ResourceBundle.getBundle factory method tries to load resource bundles with formats in the order specified by the list. The list returned by this method must have at least one String. The predefined formats are "java.class" for class-based resource bundles and "java.properties" for properties-based ones. Strings starting with "java." are reserved for future extensions and must not be used by application-defined formats.

It is not a requirement to return an immutable (unmodifiable) List. However, the returned List must not be mutated after it has been returned by getFormats.

The default implementation returns FORMAT_DEFAULT so that the ResourceBundle.getBundle factory method looks up first class-based resource bundles, then properties-based ones.

Parameters:
baseName - the base name of the resource bundle, a fully qualified class name
Returns:
a List of Strings containing formats for loading resource bundles.
Throws:
NullPointerException - if baseName is null
See Also:
FORMAT_DEFAULT, FORMAT_CLASS, FORMAT_PROPERTIES

getCandidateLocales

public List<Locale> getCandidateLocales​(String baseName,
                                        Locale locale)

Returns a List of Locales as candidate locales for baseName and locale. This method is called by the ResourceBundle.getBundle factory method each time the factory method tries finding a resource bundle for a target Locale.

The sequence of the candidate locales also corresponds to the runtime resource lookup path (also known as the parent chain), if the corresponding resource bundles for the candidate locales exist and their parents are not defined by loaded resource bundles themselves. The last element of the list must be a root locale if it is desired to have the base bundle as the terminal of the parent chain.

If the given locale is equal to Locale.ROOT (the root locale), a List containing only the root Locale must be returned. In this case, the ResourceBundle.getBundle factory method loads only the base bundle as the resulting resource bundle.

It is not a requirement to return an immutable (unmodifiable) List. However, the returned List must not be mutated after it has been returned by getCandidateLocales.

The default implementation returns a List containing Locales using the rules described below. In the description below, L, S, C and V respectively represent non-empty language, script, country, and variant. For example, [L, C] represents a Locale that has non-empty values only for language and country. The form L("xx") represents the (non-empty) language value is "xx". For all cases, Locales whose final component values are empty strings are omitted.

  1. For an input Locale with an empty script value, append candidate Locales by omitting the final component one by one as below:
    • [L, C, V]
    • [L, C]
    • [L]
    • Locale.ROOT
  2. For an input Locale with a non-empty script value, append candidate Locales by omitting the final component up to language, then append candidates generated from the Locale with country and variant restored:
    • [L, S, C, V]
    • [L, S, C]
    • [L, S]
    • [L, C, V]
    • [L, C]
    • [L]
    • Locale.ROOT
  3. For an input Locale with a variant value consisting of multiple subtags separated by underscore, generate candidate Locales by omitting the variant subtags one by one, then insert them after every occurrence of Locales with the full variant value in the original list. For example, if the variant consists of two subtags V1 and V2:
    • [L, S, C, V1, V2]
    • [L, S, C, V1]
    • [L, S, C]
    • [L, S]
    • [L, C, V1, V2]
    • [L, C, V1]
    • [L, C]
    • [L]
    • Locale.ROOT
  4. Special cases for Chinese. When an input Locale has the language "zh" (Chinese) and an empty script value, either "Hans" (Simplified) or "Hant" (Traditional) might be supplied, depending on the country. When the country is "CN" (China) or "SG" (Singapore), "Hans" is supplied. When the country is "HK" (Hong Kong SAR China), "MO" (Macau SAR China), or "TW" (Taiwan), "Hant" is supplied. For all other countries or when the country is empty, no script is supplied. For example, for Locale("zh", "CN") , the candidate list will be:
    • [L("zh"), S("Hans"), C("CN")]
    • [L("zh"), S("Hans")]
    • [L("zh"), C("CN")]
    • [L("zh")]
    • Locale.ROOT
    For Locale("zh", "TW"), the candidate list will be:
    • [L("zh"), S("Hant"), C("TW")]
    • [L("zh"), S("Hant")]
    • [L("zh"), C("TW")]
    • [L("zh")]
    • Locale.ROOT
  5. Special cases for Norwegian. Both Locale("no", "NO", "NY") and Locale("nn", "NO") represent Norwegian Nynorsk. When a locale's language is "nn", the standard candidate list is generated up to [L("nn")], and then the following candidates are added:
    • [L("no"), C("NO"), V("NY")]
    • [L("no"), C("NO")]
    • [L("no")]
    • Locale.ROOT
    If the locale is exactly Locale("no", "NO", "NY"), it is first converted to Locale("nn", "NO") and then the above procedure is followed.

    Also, Java treats the language "no" as a synonym of Norwegian Bokmål "nb". Except for the single case Locale("no", "NO", "NY") (handled above), when an input Locale has language "no" or "nb", candidate Locales with language code "no" and "nb" are interleaved, first using the requested language, then using its synonym. For example, Locale("nb", "NO", "POSIX") generates the following candidate list:

    • [L("nb"), C("NO"), V("POSIX")]
    • [L("no"), C("NO"), V("POSIX")]
    • [L("nb"), C("NO")]
    • [L("no"), C("NO")]
    • [L("nb")]
    • [L("no")]
    • Locale.ROOT
    Locale("no", "NO", "POSIX") would generate the same list except that locales with "no" would appear before the corresponding locales with "nb".

The default implementation uses an ArrayList that overriding implementations may modify before returning it to the caller. However, a subclass must not modify it after it has been returned by getCandidateLocales.

For example, if the given baseName is "Messages" and the given locale is Locale("ja", "", "XX"), then a List of Locales: 

Locale("ja", "", "XX")
     Locale("ja")
     Locale.ROOT
is returned. And if the resource bundles for the "ja" and "" Locales are found, then the runtime resource lookup path (parent chain) is: 
Messages_ja -> Messages
Parameters:
baseName - the base name of the resource bundle, a fully qualified class name
locale - the locale for which a resource bundle is desired
Returns:
a List of candidate Locales for the given locale
Throws:
NullPointerException - if baseName or locale is null

getFallbackLocale

public Locale getFallbackLocale​(String baseName,
                                Locale locale)

Returns a Locale to be used as a fallback locale for further resource bundle searches by the ResourceBundle.getBundle factory method. This method is called from the factory method every time when no resulting resource bundle has been found for baseName and locale, where locale is either the parameter for ResourceBundle.getBundle or the previous fallback locale returned by this method.

The method returns null if no further fallback search is desired.

The default implementation returns the default Locale if the given locale isn't the default one. Otherwise, null is returned.

Parameters:
baseName - the base name of the resource bundle, a fully qualified class name for which ResourceBundle.getBundle has been unable to find any resource bundles (except for the base bundle)
locale - the Locale for which ResourceBundle.getBundle has been unable to find any resource bundles (except for the base bundle)
Returns:
a Locale for the fallback search, or null if no further fallback search is desired.
Throws:
NullPointerException - if baseName or locale is null

newBundle

public ResourceBundle newBundle​(String baseName,
                                Locale locale,
                                String format,
                                ClassLoader loader,
                                boolean reload)
                         throws IllegalAccessException,
                                InstantiationException,
                                IOException

Instantiates a resource bundle for the given bundle name of the given format and locale, using the given class loader if necessary. This method returns null if there is no resource bundle available for the given parameters. If a resource bundle can't be instantiated due to an unexpected error, the error must be reported by throwing an Error or Exception rather than simply returning null.

If the reload flag is true, it indicates that this method is being called because the previously loaded resource bundle has expired.

Implementation Requirements:
Resource bundles in named modules are subject to the encapsulation rules specified by Module.getResourceAsStream. A resource bundle in a named module visible to the given class loader is accessible when the package of the resource file corresponding to the resource bundle is open unconditionally.

The default implementation instantiates a ResourceBundle as follows.

  • The bundle name is obtained by calling toBundleName(baseName, locale).
  • If format is "java.class", the Class specified by the bundle name is loaded with the given class loader. If the Class is found and accessible then the ResourceBundle is instantiated. The resource bundle is accessible if the package of the bundle class file is open unconditionally; otherwise, IllegalAccessException will be thrown. Note that the reload flag is ignored for loading class-based resource bundles in this default implementation.
  • If format is "java.properties", toResourceName(bundlename, "properties") is called to get the resource name. If reload is true, load.getResource is called to get a URL for creating a URLConnection. This URLConnection is used to disable the caches of the underlying resource loading layers, and to get an InputStream. Otherwise, loader.getResourceAsStream is called to get an InputStream. Then, a PropertyResourceBundle is constructed with the InputStream.
  • If format is neither "java.class" nor "java.properties", an IllegalArgumentException is thrown.
Parameters:
baseName - the base bundle name of the resource bundle, a fully qualified class name
locale - the locale for which the resource bundle should be instantiated
format - the resource bundle format to be loaded
loader - the ClassLoader to use to load the bundle
reload - the flag to indicate bundle reloading; true if reloading an expired resource bundle, false otherwise
Returns:
the resource bundle instance, or null if none could be found.
Throws:
NullPointerException - if bundleName, locale, format, or loader is null, or if null is returned by toBundleName
IllegalArgumentException - if format is unknown, or if the resource found for the given parameters contains malformed data.
ClassCastException - if the loaded class cannot be cast to ResourceBundle
IllegalAccessException - if the class or its nullary constructor is not accessible.
InstantiationException - if the instantiation of a class fails for some other reason.
ExceptionInInitializerError - if the initialization provoked by this method fails.
SecurityException - If a security manager is present and creation of new instances is denied. See Class.newInstance() for details.
IOException - if an error occurred when reading resources using any I/O operations
See Also:
ResourceBundleProvider.getBundle(String, Locale)

getTimeToLive

public long getTimeToLive​(String baseName,
                          Locale locale)

Returns the time-to-live (TTL) value for resource bundles that are loaded under this ResourceBundle.Control. Positive time-to-live values specify the number of milliseconds a bundle can remain in the cache without being validated against the source data from which it was constructed. The value 0 indicates that a bundle must be validated each time it is retrieved from the cache. TTL_DONT_CACHE specifies that loaded resource bundles are not put in the cache. TTL_NO_EXPIRATION_CONTROL specifies that loaded resource bundles are put in the cache with no expiration control.

The expiration affects only the bundle loading process by the ResourceBundle.getBundle factory method. That is, if the factory method finds a resource bundle in the cache that has expired, the factory method calls the needsReload method to determine whether the resource bundle needs to be reloaded. If needsReload returns true, the cached resource bundle instance is removed from the cache. Otherwise, the instance stays in the cache, updated with the new TTL value returned by this method.

All cached resource bundles are subject to removal from the cache due to memory constraints of the runtime environment. Returning a large positive value doesn't mean to lock loaded resource bundles in the cache.

The default implementation returns TTL_NO_EXPIRATION_CONTROL.

Parameters:
baseName - the base name of the resource bundle for which the expiration value is specified.
locale - the locale of the resource bundle for which the expiration value is specified.
Returns:
the time (0 or a positive millisecond offset from the cached time) to get loaded bundles expired in the cache, TTL_NO_EXPIRATION_CONTROL to disable the expiration control, or TTL_DONT_CACHE to disable caching.
Throws:
NullPointerException - if baseName or locale is null

needsReload

public boolean needsReload​(String baseName,
                           Locale locale,
                           String format,
                           ClassLoader loader,
                           ResourceBundle bundle,
                           long loadTime)

Determines if the expired bundle in the cache needs to be reloaded based on the loading time given by loadTime or some other criteria. The method returns true if reloading is required; false otherwise. loadTime is a millisecond offset since the Calendar Epoch.

The calling ResourceBundle.getBundle factory method calls this method on the ResourceBundle.Control instance used for its current invocation, not on the instance used in the invocation that originally loaded the resource bundle.

The default implementation compares loadTime and the last modified time of the source data of the resource bundle. If it's determined that the source data has been modified since loadTime, true is returned. Otherwise, false is returned. This implementation assumes that the given format is the same string as its file suffix if it's not one of the default formats, "java.class" or "java.properties".

Parameters:
baseName - the base bundle name of the resource bundle, a fully qualified class name
locale - the locale for which the resource bundle should be instantiated
format - the resource bundle format to be loaded
loader - the ClassLoader to use to load the bundle
bundle - the resource bundle instance that has been expired in the cache
loadTime - the time when bundle was loaded and put in the cache
Returns:
true if the expired bundle needs to be reloaded; false otherwise.
Throws:
NullPointerException - if baseName, locale, format, loader, or bundle is null

toBundleName

public String toBundleName​(String baseName,
                           Locale locale)

Converts the given baseName and locale to the bundle name. This method is called from the default implementation of the newBundle and needsReload methods.

This implementation returns the following value: 

baseName + "_" + language + "_" + script + "_" + country + "_" + variant
where language, script, country, and variant are the language, script, country, and variant values of locale, respectively. Final component values that are empty Strings are omitted along with the preceding '_'. When the script is empty, the script value is omitted along with the preceding '_'. If all of the values are empty strings, then baseName is returned.

For example, if baseName is "baseName" and locale is Locale("ja", "", "XX"), then "baseName_ja_ _XX" is returned. If the given locale is Locale("en"), then "baseName_en" is returned.

Overriding this method allows applications to use different conventions in the organization and packaging of localized resources.

Parameters:
baseName - the base name of the resource bundle, a fully qualified class name
locale - the locale for which a resource bundle should be loaded
Returns:
the bundle name for the resource bundle
Throws:
NullPointerException - if baseName or locale is null
See Also:
AbstractResourceBundleProvider.toBundleName(String, Locale)

toResourceName

public final String toResourceName​(String bundleName,
                                   String suffix)

Converts the given bundleName to the form required by the ClassLoader.getResource method by replacing all occurrences of '.' in bundleName with '/' and appending a '.' and the given file suffix. For example, if bundleName is "foo.bar.MyResources_ja_JP" and suffix is "properties", then "foo/bar/MyResources_ja_JP.properties" is returned.

Parameters:
bundleName - the bundle name
suffix - the file type suffix
Returns:
the converted resource name
Throws:
NullPointerException - if bundleName or suffix is null