Puzz1.java

package puzz;

import java.util.*;
import static java.util.stream.Collectors.*;

public class Puzz1 {

    public static void main(String[] args) {
        final Puzz1 puzz = new Puzz1();
        puzz.test();
    }

    Source source = new Source();
    Target target = new Target();

    public static class FeatureData {

        private String name;
        private String data;

        public String getName() {
            return name;
        }

        public void setName(String name) {
            this.name = name;
        }

        public String getData() {
            return data;
        }

        public void setData(String data) {
            this.data = data;
        }
    }

    public static class Classification {
        private List<FeatureData> features = new ArrayList<>();

        public List<FeatureData> getFeatures() {
            return features;
        }

        public void setFeatures(List<FeatureData> features) {
            this.features = features;
        }
    }

    public static class Source {
        private List<Classification> classifications = new ArrayList<>();

        public List<Classification> getClassifications() {
            return classifications;
        }

        public void setClassifications(List<Classification> classifications) {
            this.classifications = classifications;
        }
    }

    public static class Target {
        private Map<String, List<String>> features;

        public Map<String, List<String>> getFeatures() {
            return features;
        }

        public void setFeatures(Map<String, List<String>> features) {
            this.features = features;
        }
    }

    private List<String> getStringValues(FeatureData data) {
        return Arrays.asList(data.getData().split(" "));
    }

    private List<String> mergeLists(List<String> a, List<String> b) {
        final ArrayList<String> result = new ArrayList<>(a);
        result.addAll(b);
        return result;
    }

    void test() {
        Optional.ofNullable(source.getClassifications())
                .map(classifications -> classifications.stream()
                        .flatMap(classification -> classification.getFeatures().stream())
                        .collect(toMap(FeatureData::getName, this::getStringValues)))
                .ifPresent(target::setFeatures);

        Optional.ofNullable(source.getClassifications())
                .map(classifications -> classifications.stream()
                        .flatMap(classification -> classification.getFeatures().stream())
                        .collect(toMap(FeatureData::getName, this::getStringValues, this::mergeLists, HashMap::new)))
                .ifPresent(target::setFeatures);
    }
}