Class MessageFormatter
Overview of MessageFormatter
In ICU4J, the MessageFormatter
class is the next iteration of MessageFormat
.
This new version will build on the lessons learned from using MessageFormat for 25 years
in various environments, when used directly or as a base for other public APIs.
The effort to design a succesor to MessageFormat
will result in a specification
referred to as MessageFormat 2.0.
The reasoning for this effort is shared in the
“Why
MessageFormat needs a successor” document.
MessageFormat 2.0 will be more modular and easier to port and backport. It will also provide extension points via interfaces to allow users to supply new formatters and selectors without having to modify the specification. ICU will eventually include support for new formatters, such as intervals, relative time, lists, measurement units, personal names, and more, as well as the ability for users to supply their own custom implementations. These will potentially support use cases like grammatical gender, inflection, markup regimes (such as those require for text-to-speech), and other complex message management needs.
The MessageFormat Working Group, which develops the new data model, semantics, and syntax, is hosted on GitHub. The current specification for the syntax and data model can be found here.
This technical preview implements enough functions for MessageFormatter
to be useful in many situations,
but the final set of functions and the parameters accepted by those functions is not yet finalized.
Examples
Basic usage
import static org.junit.Assert.assertEquals; import java.util.Date; import java.util.HashMap; import java.util.Locale; import java.util.Map; import com.ibm.icu.message2.MessageFormatter; @Test public void testMf2() { final Locale enGb = Locale.forLanguageTag("en-GB"); Mapinvalid input: '<'String, Object> arguments = new HashMapinvalid input: '<'>(); arguments.put("name", "John"); arguments.put("exp", new Date(1679971371000L)); // March 27, 2023, 7:42:51 PM MessageFormatter mf2 = MessageFormatter.builder() .setPattern("{Hello {$name}, your card expires on {$exp :datetime skeleton=yMMMdE}!}") .setLocale(enGb) .build(); assertEquals( "Hello John, your card expires on Mon, 27 Mar 2023!", mf2.formatToString(arguments)); }
Placeholder examples
Code to set runtime value for placeholder | Examples of placeholder in message pattern |
---|---|
arguments.put("name", "John") |
}$name~ |
arguments.put("exp", new Date(…)) |
}$exp :datetime skeleton=yMMMdE~ }$exp :datetime datestyle=full~ |
arguments.put("val", 3.141592653) |
}$val~ }$val :number skeleton=(.####)~ |
No argument for fixed values known at build time | }(123456789.531) :number~ |
Plural selection message
@Test public void testMf2Selection() { final String message = "match {$count :plural}\n" + " when one {You have one notification.}\n" + " when * {You have {$count} notifications.}\n"; final Locale enGb = Locale.forLanguageTag("en-GB"); Mapinvalid input: '<'String, Object> arguments = new HashMapinvalid input: '<'>(); MessageFormatter mf2 = MessageFormatter.builder() .setPattern(message) .setLocale(enGb) .build(); arguments.put("count", 1); assertEquals( "You have one notification.", mf2.formatToString(arguments)); arguments.put("count", 42); assertEquals( "You have 42 notifications.", mf2.formatToString(arguments)); }
Built-in formatter functions
The tech preview implementation comes with formatters for numbers (number
),
date / time (datetime
),
plural selectors (plural
and selectordinal
),
and general selector (select
),
very similar to what MessageFormat offers.
The ICU test code
covers most features, and has examples of how to make custom placeholder formatters;
you can look for classes that implement com.ibm.icu.message2.FormatterFactory
(they are named Custom*Test.java
).
Functions currently implemented
These are the functions interpreted right now:
datetime |
Similar to MessageFormat's date and time . |
datestyle and timestyle Similar to argStyle : short | medium | long | full .Same values are accepted, but we can use both in one placeholder, for example {$due :datetime datestyle=full timestyle=long} .
| |
pattern Similar to argStyle = argStyleText .This is bad i18n practice, and will probably be dropped. This is included just to support migration to MessageFormat 2. | |
skeleton Same as argStyle = argSkeletonText .These are the date/time skeletons as supported by SimpleDateFormat .
| |
number |
Similar to MessageFormat's number . |
skeleton These are the number skeletons as supported by NumberFormatter . | |
minimumFractionDigits Only implemented to be able to pass the unit tests from the ECMA tech preview implementation, which prefers options bags to skeletons. TBD if the final function will support skeletons, option backs, or both. | |
offset Used to support plural with an offset. | |
identity | Returns the direct string value of the argument (calling toString() ). |
plural |
Similar to MessageFormat's plural . |
skeleton These are the number skeletons as supported by NumberFormatter .Can also be indirect, from a local variable of type number (recommended). | |
offset Used to support plural with an offset. Can also be indirect, from a local variable of type number (recommended). | |
selectordinal |
Similar to MessageFormat's selectordinal .For now it accepts the same parameters as plural , although there is no use case for them.TBD if this will be merged into plural (with some kind option) or not. |
select | Literal match, same as MessageFormat's select . |
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Nested Class Summary
Nested ClassesModifier and TypeClassDescriptionstatic class
Deprecated.This API is for technology preview only. -
Method Summary
Modifier and TypeMethodDescriptionstatic MessageFormatter.Builder
builder()
Deprecated.This API is for technology preview only.Deprecated.This API is for technology preview only.formatToString
(Map<String, Object> arguments) Deprecated.This API is for technology preview only.Deprecated.This API is for technology preview only.Deprecated.This API is for technology preview only.Deprecated.This API is for technology preview only.
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Method Details
-
builder
Deprecated.This API is for technology preview only.Creates a builder.- Returns:
- the Builder.
-
getLocale
Deprecated.This API is for technology preview only.Get the locale to use for all the formatting and selections in the currentMessageFormatter
.- Returns:
- the locale.
-
getPattern
Deprecated.This API is for technology preview only.Get the pattern (the serialized message in MessageFormat 2 syntax) of the currentMessageFormatter
.If the
MessageFormatter
was created from anMf2DataModel
the this string is generated from that model.- Returns:
- the pattern.
-
getDataModel
Deprecated.This API is for technology preview only.Give public access to the message data model.This data model is similar to the functionality we have today in
MessagePatternUtil
maybe even a bit more higher level.We can also imagine a model where one parses the string syntax, takes the data model, modifies it, and then uses that modified model to create a
MessageFormatter
.- Returns:
- the data model.
-
formatToString
Deprecated.This API is for technology preview only.Formats a map of objects by iterating over the MessageFormat's pattern, with the plain text “as is” and the arguments replaced by the formatted objects.- Parameters:
arguments
- a map of objects to be formatted and substituted.- Returns:
- the string representing the message with parameters replaced.
- Throws:
IllegalArgumentException
- when something goes wrong (for example wrong argument type, or null arguments, etc.)
-
format
Deprecated.This API is for technology preview only.Not yet implemented: formats a map of objects by iterating over the MessageFormat's pattern, with the plain text “as is” and the arguments replaced by the formatted objects.- Parameters:
arguments
- a map of objects to be formatted and substituted.- Returns:
- the
FormattedMessage
class representing the message with parameters replaced.
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