LocalDatabaseModel.java

import java.io.*;
import java.util.*;
import java.util.stream.*;
import com.google.gson.*;

public final class LocalDatabaseModel implements Model {
    private final JsonObject root;

    public LocalDatabaseModel() {
        try(var reader = new InputStreamReader(Model.class.getResourceAsStream("/dsonames.json"))) {
            root = JsonParser.parseReader(reader).getAsJsonObject();
        } catch (IOException e) {
            throw new IOError(e);
        }
    }

    public List<String> names() {
        var result = new ArrayList<String>();
        for (var entry : root.entrySet()) {
            var planet = entry.getValue().getAsJsonObject();
            result.add(planet.get("name").getAsString());
        }
        return result;
    }

    public Map<String, String> translatedNames(String language) {
        return root.entrySet().stream()
                   .map(e -> e.getValue().getAsJsonObject())
                   .filter(p -> p.has(language))
                   .collect(Collectors.toMap(p -> p.get("name").getAsString(), p -> p.get(language).getAsString(), (a, b) -> a));
    }
}