Package com.ibm.icu.message2

Class MessageFormatter

  • public class MessageFormatter
extends Object

    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 functions 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");
     Map<String, Object> arguments = new HashMap<>();
     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");
    Map<String, Object> arguments = new HashMap<>();

    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 formatter functions 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.FunctionFactory (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.

    Status:
    Draft ICU 78.

    • Method Detail

      • builder

        public static MessageFormatter.Builder builder()
        Creates a builder.
        Returns:
        the Builder.
        Status:
        Draft ICU 78.

      • getLocale

        public Locale getLocale()
        Get the locale to use for all the formatting and selections in the current MessageFormatter.
        Returns:
        the locale.
        Status:
        Draft ICU 78.

      • getPattern

        public String getPattern()
        Get the pattern (the serialized message in MessageFormat 2 syntax) of the current MessageFormatter.

        If the MessageFormatter was created from an MFDataModel the this string is generated from that model.

        Returns:
        the pattern.
        Status:
        Draft ICU 78.

      • getDataModel

        @Deprecated
public MFDataModel.Message 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.
        Status:
        Technology Preview. This API is still in the early stages of development. Use at your own risk.

      • formatToString

        public String formatToString​(Map<String,​Object> arguments)
        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.)
        Status:
        Draft ICU 78.

      • format

        @Deprecated
public FormattedMessage format​(Map<String,​Object> arguments)
        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.
        Status:
        Technology Preview. This API is still in the early stages of development. Use at your own risk.