org.apache.jetspeed.i18n
Class KeyedMessage

java.lang.Object
  org.apache.jetspeed.i18n.KeyedMessage

All Implemented Interfaces:

Serializable

public class KeyedMessage
extends Object
implements 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
           }
       }    
 

Version:

$Id: KeyedMessage.java 516448 2007-03-09 16:25:47Z ate $

Author:

Ate Douma

See Also:

Serialized Form

Field Summary

private Object[]	arguments Optional message format arguments which can only be set using a derived KeyedMessage using the create(Object[])method(s).
private Class	containingClass The class in which this instance is defined as a static Field.
private String	key Dynamically derived key based on the definingClass name, postfixed with the static field name of this instance
static String	KEYED_MESSAGE_BUNDLE_FIELD_NAME Static String Field name searched for in the class defining a KeyedMessage containing the default resource bundle to use for translation.
private String	message Default message used when key couldn't be looked up in the default or a specified resource bundle
private boolean	resolved Indicates if this instance could be resolved.
private static HashMap	resourceNameMap Map caching default resource bundle names keyed on containingClass
private static String	UNRESOLVED_KEY Key value for an unresolved KeyMessage.

Constructor Summary

protected	KeyedMessage(KeyedMessage source, Object[] arguments) Constructs a derived KeyedMessage from another KeyedMessage to provide additional message format arguments.
	KeyedMessage(String message) Constructs a new KeyedMessage which will dynamically derive its own getKey().

Method Summary

protected KeyedMessage	create(KeyedMessage source, Object[] arguments) Extendable KeyedMessage factory
KeyedMessage	create(Object o) Simplied version of create(Object[])with only one argument
KeyedMessage	create(Object[] arguments) Creates a derived KeyedMessage from this instance to provide additional message format arguments.
KeyedMessage	create(Object o1, Object o2) Simplied version of create(Object[])with only two arguments
KeyedMessage	create(Object o1, Object o2, Object o3) Simplied version of create(Object[])with only three arguments
boolean	equals(Object otherObject)
private String	format(String message) Formats a message using MessageFormat if arguments are defined, otherwise simply returns the argument.
Object	getArgument(int index)
Object[]	getArguments()
ResourceBundle	getBundle() Loads and returns the default ResourceBundle for this instance using the current Locale.
ResourceBundle	getBundle(Locale locale) Loads and returns a Locale specific default ResourceBundle for this instance.
String	getKey() Dynamically derived key based on the definingClass name, postfixed with the static field name of this instance.
String	getMessage()
String	getMessage(Locale locale)
String	getMessage(ResourceBundle bundle)
private String	getResourceName()
private void	resolve()
String	toString()

Methods inherited from class java.lang.Object

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

Field Detail

KEYED_MESSAGE_BUNDLE_FIELD_NAME

public static final String KEYED_MESSAGE_BUNDLE_FIELD_NAME

Static String Field name searched for in the class defining a KeyedMessage containing the default resource bundle to use for translation.
Note: this Field is looked up using definingClass.getField thus it may also be defined in a superclass or interface of the definingClass.

See Also:

Constant Field Values

UNRESOLVED_KEY

private static final String UNRESOLVED_KEY

Key value for an unresolved KeyMessage.

resourceNameMap

private static final HashMap resourceNameMap

Map caching default resource bundle names keyed on containingClass

message

private String message

Default message used when key couldn't be looked up in the default or a specified resource bundle

key

private String key

Dynamically derived key based on the definingClass name, postfixed with the static field name of this instance

See Also:

getKey()

arguments

private Object[] arguments

Optional message format arguments which can only be set using a derived KeyedMessage using the create(Object[])method(s).

containingClass

private Class containingClass

The class in which this instance is defined as a static Field.

resolved

private boolean resolved

Indicates if this instance could be resolved.

Constructor Detail

KeyedMessage

protected KeyedMessage(KeyedMessage source,
                       Object[] arguments)

Constructs a derived KeyedMessage from another KeyedMessage to provide additional message format arguments.

Parameters:

source - the KeyedMessage to derive this instance from

arguments - this instance specific message format arguments

See Also:

create(Object[])

KeyedMessage

public KeyedMessage(String message)

Constructs a new KeyedMessage which will dynamically derive its own getKey().

Parameters:

message - the default message used when the getKey()could not be found in the default or a specified resource bundle.

Method Detail

getResourceName

private String getResourceName()

resolve

private void resolve()

See Also:

KeyedMessage

format

private String format(String message)

Formats a message using MessageFormat if arguments are defined, otherwise simply returns the argument.

Parameters:

message - the message format

Returns:

formatted message

create

protected KeyedMessage create(KeyedMessage source,
                              Object[] arguments)

Extendable KeyedMessage factory

Parameters:

source - the source to copy from

arguments - the optional message format arguments

Returns:

copied instance with new arguments set

create

public KeyedMessage create(Object[] arguments)

Creates a derived KeyedMessage from this instance to provide additional message format arguments.
The new instance will be equals(Object)to this instance with only different arguments.

Note: the argument objects should be lightweight types and preferably Serializable instances

Parameters:

arguments - The derived instance specific message format arguments

Returns:

derived KeyedMessage equalto this with its own message format arguments

create

public KeyedMessage create(Object o)

Simplied version of create(Object[])with only one argument

Parameters:

single - message format argument

Returns:

derived KeyedMessage equalto this with its own message format argument

See Also:

create(Object[])

create

public KeyedMessage create(Object o1,
                           Object o2)

Simplied version of create(Object[])with only two arguments

Parameters:

single - message format argument

Returns:

derived KeyedMessage equalto this with its own message format arguments

See Also:

create(Object[])

create

public KeyedMessage create(Object o1,
                           Object o2,
                           Object o3)

Simplied version of create(Object[])with only three arguments

Parameters:

single - message format argument

Returns:

derived KeyedMessage equalto this with its own message format arguments

See Also:

create(Object[])

getKey

public final String getKey()

Dynamically derived key based on the definingClass name, postfixed with the static field name of this instance.

Format:
<containingClass.name>.<staticInstanceField.name>

If this instance couldn't be resolved, generic value UNRESOLVED_KEY will have been set.

Returns:

derived key

getBundle

public ResourceBundle getBundle(Locale locale)

Loads and returns a Locale specific default ResourceBundle for this instance.
If this instance couldn't be resolvedor the bundle couldn't be loadednull will be returned.
The ResourceBundle will be loaded using the containingClassits ClassLoader.

Parameters:

locale - the Locale to lookup the locale specific default ResourceBundle

Returns:

a Locale specific default ResourceBundle

getBundle

public ResourceBundle getBundle()

Loads and returns the default ResourceBundle for this instance using the current Locale.

Returns:

the default ResourceBundle for the current Locale

See Also:

getBundle(Locale), CurrentLocale

getMessage

public String getMessage()

Returns:

formatted message using the default ResourceBundle using the current Locale.

See Also:

getBundle()

getMessage

public String getMessage(ResourceBundle bundle)

Parameters:

bundle - a specific ResourceBundle defining this instance key

Returns:

formatted message using a specific ResourceBundle.

getMessage

public String getMessage(Locale locale)

Parameters:

locale - a specific Locale

Returns:

formatted message using the default ResourceBundle using a specific Locale.

getArguments

public Object[] getArguments()

Returns:

the arguments defined for this derivedinstance

See Also:

create(Object[])

getArgument

public Object getArgument(int index)

Parameters:

index - argument number

Returns:

an argument defined for this derivedinstance

toString

public String toString()

Overrides:

toString in class Object

Returns:

formatted message using the default ResourceBundle using the current Locale.

See Also:

getMessage()

equals

public boolean equals(Object otherObject)

Overrides:

equals in class Object

Parameters:

otherObject - KeyedMessage instance to compare with

Returns:

true only if otherObject is a KeyedMessage derivedfrom this instance (or visa versa) and (thus both are) resolved.

See Also:

create(Object[]), resolve()