public interface Messages extends LocalizableResource
GWT.create(class) to "instantiate" an interface that
extends Messages returns an instance of an automatically
generated subclass that is implemented using message templates selected based
on locale. Message templates are based on a subset of the format used by
MessageFormat. Note in particular that single quotes are
used to quote other characters, and should be doubled for a literal single
quote.
Locale is specified at run time using a meta tag or query string as described
for Localizable.
MessagesMessages, begin by defining an interface that extends
it. Each interface method is referred to as a message accessor, and
its corresponding message template is loaded based on the key for that
method. The default key is simply the unqualified name of the method, but can
be specified directly with an @Key annotation or a different
generation method using @GenerateKeys. Additionally, if
plural forms are used on a given method the plural form is added as a suffix
to the key, such as widgets[one] for the singular version of
the widgets message. The resulting key is used to find
translated versions of the message from any supported input file, such as
Java properties files. For example,
public interface GameStatusMessages extends Messages {
/**
* @param username the name of a player
* @param numTurns the number of turns remaining
* @return a message specifying the remaining turns for a player
*/
String turnsLeft(String username, int numTurns);
/**
* @param numPoints the number of points
* @return a message describing the current score for the current player
*/
String currentScore(int numPoints);
}
turnsLeft and
currentScore in an associated properties file, formatted as
message templates taking two arguments and one argument, respectively. For
example, the following properties would correctly bind to the
GameStatusMessages interface:
turnsLeft = Turns left for player ''{0}'': {1}
currentScore = Current score: {0}
The following example demonstrates how to use constant accessors defined in the interface above:
public void beginNewGameRound(String username) {
GameStatusMessages messages = (GameStatusMessages) GWT.create(GameStatusMessages.class);
// Tell the new player how many turns he or she has left.
int turnsLeft = computeTurnsLeftForPlayer(username);
showMessage(messages.turnsLeft(username, turnsLeft));
// Tell the current player his or her score.
int currentScore = computeScore(username);
setCurrentPlayer(username);
showMessage(messages.currentScore(currentScore));
}
The following example shows how to use annotations to store the default strings in the source file itself, rather than needing a properties file (you still need properties files for the translated strings):
public interface GameStatusMessagesAnnot extends Messages {
/**
* @param username the name of a player
* @param numTurns the number of turns remaining
* @return a message specifying the remaining turns for a player
*/
@DefaultMessage("Turns left for player ''{0}'': {1}")
String turnsLeft(String username, int numTurns);
/**
* @param numPoints the number of points
* @return a message describing the current score for the current player
*/
@DefaultMessage("Current score: {0}")
String currentScore(int numPoints);
}
In this example, calling msg.turnsLeft("John", 13) would
return the string "Turns left for player 'John': 13".
String methodName(optional-params)and parameters may be of any type. Arguments are converted into strings at runtime using Java string concatenation syntax (the '+' operator), which uniformly handles primitives,
null, and invoking
toString() to format objects.
Compile-time checks are performed to ensure that the number of placeholders
in a message template (e.g. {0}) matches the number of
parameters supplied.
Integral arguments may be used to select the proper plural form to use for
different locales. To do this, mark the particular argument with
@PluralCount (a plural rule may be specified with
@PluralCount if necessary, but you will almost never need to
do this). The actual plural forms for the default locale can be supplied in a
@PluralText annotation on the method, such as
@PluralText({"one", "You have one widget"}), or they can be
supplied in the properties file as methodkey[one]=You have one widget. Note
that non-default plural forms are not inherited between locales, because the
different locales may have different plural rules (especially default and
anything else and those which use different scripts such as sr_Cyrl and
sr_Latn [one of which would likely be the default], but also subtle cases
like pt and pt_BR).
Additionally, individual arguments can be marked as optional (ie, GWT will
not give an error if a particular translation does not reference the
argument) with the @Optional annotation, and an example may be supplied to
the translator with the @Example(String) annotation.
@Generate(format = "com.google.gwt.i18n.rebind.format.PropertiesFormat")
@DefaultLocale("en_US")
public interface MyMessages extends Messages {
@Key("1234")
@DefaultMessage("This is a plain string.")
String oneTwoThreeFour();
@DefaultMessage("You have {0} widgets")
@PluralText({"one", "You have one widget")
String widgetCount(@PluralCount int count);
@DefaultMessage("No reference to the argument")
String optionalArg(@Optional String ignored);
@DefaultMessage("Your cart total is {0,number,currency}")
@Description("The total value of the items in the shopping cart in local currency")
String totalAmount(@Example("$5.00") double amount);
@Meaning("the color")
@DefaultMessage("orange")
String orangeColor();
@Meaning("the fruit")
@DefaultMessage("orange")
String orangeFruit();
}
Messages are bound to resource files
using the same algorithm as interfaces extending Constants.
See the documentation for Constants for a description of the
algorithm.
com.google.gwt.i18n.I18N.
<module> <!-- other inherited modules, such as com.google.gwt.user.User --> <inherits name="com.google.gwt.i18n.I18N"/> <!-- additional module settings --> </module>
GWT.create(Class).| Modifier and Type | Interface and Description |
|---|---|
static interface |
Messages.AlternateMessage
Provides alternate forms of a message, such as are needed when plural
forms are used or a placeholder has known gender.
|
static interface |
Messages.DefaultMessage
Default text to be used if no translation is found (and also used as the
source for translation).
|
static interface |
Messages.Example
An example of the annotated parameter to assist translators.
|
static interface |
Messages.Offset
Ignored except on parameters also tagged with
Messages.PluralCount, and
provides an offset to be subtracted from the value before a plural rule
is chosen or the value is formatted. |
static interface |
Messages.Optional
Indicates the specified parameter is optional and need not appear in a
particular translation of this message.
|
static interface |
Messages.PluralCount
Provides multiple plural forms based on a count.
|
static interface |
Messages.PluralText
Deprecated.
use
Messages.AlternateMessage instead |
static interface |
Messages.Select
Provides multiple forms based on a dynamic parameter.
|
LocalizableResource.DefaultLocale, LocalizableResource.Description, LocalizableResource.Generate, LocalizableResource.GeneratedFrom, LocalizableResource.GenerateKeys, LocalizableResource.Key, LocalizableResource.Meaning