How to filter username in a List of Users ignoring accented characters.

FilterObjectStringStreamTest.java

import com.google.common.collect.ImmutableList;
import org.assertj.core.util.Strings;
import org.junit.Test;

import java.text.Normalizer;
import java.util.List;
import java.util.Locale;
import java.util.function.Predicate;
import java.util.regex.Pattern;
import java.util.stream.Collectors;

import static org.assertj.core.api.Assertions.assertThat;

public class FilterObjectStringStreamTest {
    private static final Pattern PATTERN = Pattern.compile("\\p{InCombiningDiacriticalMarks}+");

    private List<User> getUsers() {
        int i = 1;
        return ImmutableList.of(
                new User(i++, "João Saldanha"),
                new User(i++, "João-Saldanha"),
                new User(i++, "João:Saldanha"),
                new User(i++, "Joao Silva"),
                new User(i++, "Graça Maria"),
                new User(i++, "Jorge Lourenço"),
                new User(i++, "Fábio Saldanha"),
                new User(i++, "Fabiano Gonçalves")
        );
    }

    static class User {
        int id;
        String name;

        public User(int id, String name) {
            this.id = id;
            this.name = name;
        }

        public int id() {
            return id;
        }

        public String name() {
            return name;
        }
    }

    public static String deAccent(String str) {
        return PATTERN.matcher(Normalizer.normalize(str, Normalizer.Form.NFD)).replaceAll("");
    }

    public static Predicate<User> contains(String query) {
        if (Strings.isNullOrEmpty(query))
            return user -> false;
        return user -> deAccent(user.name()).toLowerCase(Locale.ROOT).contains(deAccent(query).toLowerCase(Locale.ROOT));
    }

    private List<User> filterUser(String query) {
        return getUsers().stream()
                .filter(contains(query))
                .collect(Collectors.toList());
    }

    @Test
    public void filterUserTest() {
        assertThat(filterUser("João SALDANha")).hasSize(1);
        assertThat(filterUser("João-saldanha")).hasSize(1);
        assertThat(filterUser("JoAo")).hasSize(4);
        assertThat(filterUser("Graça")).hasSize(1);
        assertThat(filterUser("Graca")).hasSize(1);
        assertThat(filterUser("Fábi")).hasSize(2);
        assertThat(filterUser(null)).isEmpty();
        assertThat(filterUser("")).isEmpty();
    }
}