A new message definition and automatic translation facility: KeyedMessage.
--------------------------------------------------------------------------
Key: JS2-219
URL: http://issues.apache.org/jira/browse/JS2-219
Project: Jetspeed 2
Type: Improvement
Components: i18n and l10n
Versions: 2.0-dev/cvs
Reporter: Ate Douma
Assigned to: Ate Douma
Fix For: 2.0-dev/cvs, 2.0-M2
I've been working on enhancements of the Login Portlet to provide better
feedback to the user about login errors.
Because the exceptions thrown by the Security layer currently use statically
defined Exception messages to distinguish the different conditions, checking
which type of error occurred is very cumbersome to do. Furthermore, in some
situations the statically defined messages
are only used as templates (.e.g. a specific User/Role/Group name is postfixed)
making it even harder to compare the exceptions.
I've come up with a generic, transparent and very easy to use, i18n supporting,
message definition and automatic translation facility which also provides named
constant definitions (phew, heavy definition).
For this I created a new class org.apache.jetspeed.i18n.KeyedMessage.
As I've provided extensive documentation through javadoc I'll provide the class
level description below to explain its purpose and usage including a real ;-)
example.
I've used this KeyedMessage to replace all SecurityException constant String
messages with a KeyedMessage variant.
Furthermore, I've enhanced JetspeedException (and JetspeedRuntimeException) to
recognize Exceptions constructed using a KeyMessage, and provided a
org.apache.jetspeed.exception.JetspeedExceptionMessages.properties resource
bundle (as well as a Dutch variant) containing SecurityException translations.
After I've committed these changes, the benefit of this new facility can be
easily tested as follows:
- login as admin
- switch the locale to Dutch using the Locale Portlet
- go to the UserBrowserPortlet
- select the guest user
- try to delete the guest user
- You will see a Dutch error message saying: "De gebruiker guest is beveiligd."
(Previously, you would have been presented with: "The anonymous user is
protected.")
I didn't have to change anything in the UserBrowserPorlet or UserDetailPorlet
for this to work.
A copy of the class level documentation of
org.apache.jetspeed.i18n.KeyedMessage follows:
=========================================================================================
public class KeyedMessage extends java.lang.Object implements
java.io.Serializable
KeyedMessage provides an automatically derived i18n message key based on its
static instance definition and can be used as comparable constant too.
Purpose
-------
With a KeyedMessage a named constant message (format) can be statically defined
which automatically translate themselves for a specific locale using an
automatically derived ResourceBundle or even a specified one.
Key derivation
--------------
Because KeyedMessages are created with a default message (format), even if no
ResourceBundle or its key is defined or can't be found, message translation is
still possible.
A KeyedMessage automatically derives the ResourceBundle lookup key from its
(statically defined) instance field name using the following format:
<containingClass.name>.<staticInstanceField.name>
The containingClass is derived at construction time by analyzing the
StackTraceElements of a thrown exception. This requires the instance to be
defined as a public static field!
At first access, the key is resolved by inspecting the derived containingClass
for the declared field defining this instance.
If the KeyedMessage instance wasn't defined as public static field, the key
can't be resolved and message translation using a ResourceBundle won't be
possible. Translation using the default message will still work though.
Furthermore, this instance can't be used as comparable named constant as the
equals(Object)method will always return false in this case.
Default ResourceBundle name derivation
--------------------------------------
When the key of a KeyedMessage is resolved, the default ResourceBundle name for
message translation is retrieved from the defined public static String field
named "KEYED_MESSAGE_BUNDLE"defined in its containingClass or one of its
superClasses or interfaces.
If this field cannot be found, the fully qualified name of the containingClass
is used.
ResourceBundle names are cached in a Map for each containingClass and only
derived for the first KeyedMessage defined in a containingClass.
Again: only resolved instances can use a ResourceBundle for message translation.
Default Locale lookup
---------------------
When a message is translated without a specified Locale, CurrentLocale.get()is
used to determine the default Locale for the current Thread.
In Jetspeed, the LocalizationValve initializes the CurrentLocale on each
request. KeyedMessages accessed within the context of an Jetspeed request
therefore will always be translated using the current user Locale with the
getMessage()or toString()methods.
Default ResourceBundle lookup
If a message translation is done using the default ResourceBundle name the
ResourceBundle is retrieved using the ClassLoader of the containingClass. This
means the bundle(s) must be provided in the same context as from where the
containingClass is loaded. Usually (and preferably), this will be from the
shared classpath of the webserver.
MessageFormat parameters
------------------------
MessageFormat patterns can also be used for a KeyedMessage.
With the create(Object[])method a specialized copy of a KeyedMessage instance
can be created containing the arguments to be used during message translation.
This new copy remains equals(Object)to its source and can still be used for
named constant comparison.
For simplified usage, three create(Object),create(Object, Object)and
create(Object, Object, Object)methods are provided which delegate to
create(Object[])with their argument(s) transformed into an Object array.
Extending KeyedMessage
----------------------
An statically defined KeyedMessage can be used as a "simple" named constant.
If additional metadata is required like some kind of status, level or type
indication, the KeyedMessage class can easily be extended by providing a
specialized version of the create(KeyedMessage, Object[])copy factory.
Usage
-----
KeyedMessage has been used to replace the hardcoded SecurityException String
constants.
The ResourceBundle name used is defined by
JetspeedException.KEYED_MESSAGE_BUNDLE which is the superClass of
SecurityException.
For a different ResourceBundle to be used for SecurityException messages a
KEYED_MESSAGE_BUNDLE field can be defined in SecurityException too, overriding
the one in JetspeedException.
Example:
public class JetspeedException extends Exception {
public static final String KEYED_MESSAGE_BUNDLE =
"org.apache.jetspeed.exception.JetspeedExceptionMessages";
...
public String getMessage() {
if ( keyedMessage != null ) {
return keyedMessage.getMessage(); // translated using
current Locale and default ResourceBundle
}
return super.getMessage();
}
}
public class SecurityException extends JetspeedException {
public static final KeyedMessage USER_DOES_NOT_EXIST = new
KeyedMessage("The user {0} does not exist.");
...
}
// resource file:
org.apache.jetspeed.exception.JetspeedExceptionMessages_nl.properties
org.apache.jetspeed.security.SecurityException.USER_DOES_NOT_EXIST = De
gebruiker {0} bestaat niet.
...
public class UserManagerImpl implements UserManager {
public User getUser(String username) throws SecurityException {
...
if (null == userPrincipal) {
throw new
SecurityException(SecurityException.USER_DOES_NOT_EXIST.create(username));
}
...
}
...
}
// example get User
try {
User user = userManager.getUser(userName);
} catch (SecurityException sex) {
if (
SecurityException.USER_DOES_NOT_EXISTS.equals(sex.getKeyedMessage()) {
// handle USER_DOES_NOT_EXISTS error
}
}
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