CoordinateKit CRF

var tagProvider = new StringTagProvider("O");
var trainer = new MalletCrfTrainer(
    CompositeFeatureExtractor.of(
        LengthFeatureExtractor.<String>builder(5)
            .hasLengthFeatureMapper(len -> "HAS_LENGTH_" + len).build(),
        PatternMatchingFeatureExtractor.<String>builder("\\d+")
            .matchedFeature("IS_DIGITS").build()
    ),
    tagProvider,
    new XmlTrainingData(tagProvider)
);
trainer.train(Path.of("training.xml"), Path.of("model.crf"));