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 test() { final Locale enGb = Locale.forLanguageTag("en-GB"); Mapinvalid input: '<'String, Object> arguments = new HashMapinvalid input: '<'>(); arguments.put("name", "John"); arguments.put("exp", new Date(2023 - 1900, 2, 27, 19, 42, 51)); // March 27, 2023, 7:42:51 PM MessageFormatter mf2 = MessageFormatter.builder() .setPattern("Hello {$name}, your card expires on {$exp :datetime year=numeric month=short day=numeric weekday=short}!") .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=year=numeric month=short day=numeric weekday=short} {$exp :datetime dateStyle=full} |
arguments.put("val", 3.141592653) |
{$val} {$val :number minimumFractionDigits=5} |
No argument for fixed values known at build time | {|123456789.531| :number} |
Plural selection message
@Test public void testSelection() { final String message = ".match {$count :number}\n" + " 1 {{You have one notification.}}\n" + " * {{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
, :date
, :time
),
plural selectors (:number
with options for plural
and ordinal
selection),
and general selector (:string
),
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
).
The complete list of valid options for each function, and how they infulence the results, can be found at here.
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Nested Class Summary
Nested ClassesModifier and TypeClassDescriptionstatic class
Deprecated.This API is for technology preview only.static enum
Deprecated.This API is for technology preview only. -
Field Summary
FieldsModifier and TypeFieldDescriptionprivate final MFDataModel.Message
Deprecated.private final MessageFormatter.ErrorHandlingBehavior
Deprecated.private final MFFunctionRegistry
Deprecated.private final Locale
Deprecated.private final MFDataModelFormatter
Deprecated.private final String
Deprecated. -
Constructor Summary
ConstructorsModifierConstructorDescriptionprivate
MessageFormatter
(MessageFormatter.Builder builder) Deprecated. -
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.Deprecated.This API is for technology preview only.
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Field Details
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locale
Deprecated. -
pattern
Deprecated. -
errorHandlingBehavior
Deprecated. -
functionRegistry
Deprecated. -
dataModel
Deprecated. -
modelFormatter
Deprecated.
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Constructor Details
-
MessageFormatter
Deprecated.
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Method Details
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builder
Deprecated.This API is for technology preview only.Creates a builder.- Returns:
- the Builder.
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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.
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getErrorHandlingBehavior
Deprecated.This API is for technology preview only.Get theMessageFormatter.ErrorHandlingBehavior
to use when encountering errors in the currentMessageFormatter
.- Returns:
- the error handling behavior.
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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 anMFDataModel
the this string is generated from that model.- Returns:
- the pattern.
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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.
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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.)
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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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