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.
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(ListResourceBundle.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() {
...
}
}
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;
}
});
| Field Summary | |
|---|---|
| static final List<String> |
The class-only format List containing
"java.class".
|
| static final List<String> |
The default format List, which contains the strings
"java.class" and "java.properties", in
this order.
|
| static final List<String> |
The properties-only format List containing
"java.properties".
|
| static final long |
The time-to-live constant for not caching loaded resource bundle instances. |
| static final long |
The time-to-live constant for disabling the expiration control for loaded resource bundle instances in the cache. |
| Constructor Summary |
|---|
|
Sole constructor. |
| Method Summary | |
|---|---|
| List<Locale> |
Returns a List of Locales as candidate
locales for baseName and locale.
|
| static final ResourceBundle.Control |
Returns a ResourceBundle.Control in which the getFormats method returns the specified
formats.
|
| Locale |
Returns a Locale to be used as a fallback locale for
further resource bundle searches by the
ResourceBundle.getBundle factory method.
|
| List<String> |
Returns a List of Strings containing
formats to be used to load resource bundles for the given
baseName.
|
| static final ResourceBundle.Control |
Returns a ResourceBundle.Control in which the getFormats method returns the specified
formats and the getFallbackLocale
method returns null.
|
| long |
Returns the time-to-live (TTL) value for resource bundles that are loaded under this ResourceBundle.Control.
|
| boolean |
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 |
Instantiates a resource bundle for the given bundle name of the given format and locale, using the given class loader if necessary. |
| String |
Converts the given baseName and locale
to the bundle name.
|
| final String |
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 inherited from java.langObject |
|---|
List, which contains the strings
"java.class" and "java.properties", in
this order. This List is unmodifiable . 
public static final
long
TTL_DONT_CACHE
public static final
long
TTL_NO_EXPIRATION_CONTROL
protected ResourceBundle.Control
(
)
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 in the following sequence:
Locale(language, country, variant)
Locale(language, country)
Locale(language)
Locale.ROOT
where language, country and
variant are the language, country and variant values
of the given locale, respectively. Locales where the
final component values are empty strings are omitted.
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
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.
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.
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.
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. 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 .
public
boolean
needsReload
(
String
baseName,
Locale
locale,
String
format,
ClassLoader
loader,
ResourceBundle
bundle,
long
loadTime
)
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".
public
ResourceBundle
newBundle
(
String
baseName,
Locale
locale,
String
format,
ClassLoader
loader,
boolean
reload
)
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.
The default implementation instantiates a
ResourceBundle as follows.
format is "java.class", the
Class specified by the bundle name is loaded by calling
loadClass(String) . Then, a
ResourceBundle is instantiated by calling newInstance() . Note that the reload flag is
ignored for loading class-based resource bundles in this default
implementation.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.format is neither "java.class"
nor "java.properties", an
IllegalArgumentException is thrown.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 + "_" + country + "_" + variant
where language, country and
variant are the language, country and variant values
of locale, respectively. Final component values that
are empty Strings are 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.
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. 
Listcontaining"java.class". ThisListis unmodifiable .