[Java8] Function과 Stream을 이용한 객체 복사 테스트 예제

Java8  Function과 Stream을 이용한 객체 복사 테스트 예제이다. 

List 값 비교는 Lamda를 사용하였다. 

import com.google.common.collect.ImmutableList;
import org.apache.commons.lang.builder.ToStringBuilder;
import org.apache.commons.lang.builder.ToStringStyle;
import org.junit.Assert;
import org.junit.Test;
import static org.hamcrest.Matchers.*;
import java.util.List;
import java.util.function.Function;
import java.util.stream.Collectors;


public class ConvertObjectTest {

    Function<OneMember, OnePerson> convertFunction = new Function<OneMember, OnePerson>() {
        public OnePerson apply(OneMember member) {
            return new OnePerson(member.id, member.name);
        }
    };

    @Test
    public void convertObjectWithFunctionTest() {
        OneMember member = new OneMember(1, "Samuel");
        OnePerson person = convertFunction.apply(member);
        Assert.assertEquals(member.name, person.name);
    }

    @Test
    public void convertObjectListWithFunctionTest() {
        OneMember samuel = new OneMember(1, "Samuel");
        OneMember daisy = new OneMember(2, "Daisy");
        OneMember matt = new OneMember(3, "Matt");
        ImmutableList<OneMember> immutableMemberList = ImmutableList.of(samuel, daisy, matt);

        List<OnePerson> personList = immutableMemberList.stream()
                .map(convertFunction)
                .collect(Collectors.<OnePerson>toList());

        personList.sort((OnePerson h1, OnePerson h2) -> h1.id.compareTo(h2.id));
        Assert.assertThat(personList.get(0), equalTo(new OnePerson(1, "Samuel")));
        Assert.assertThat(personList.get(1), equalTo(new OnePerson(2, "Daisy")));
        Assert.assertThat(personList.get(2), equalTo(new OnePerson(3, "Matt")));
    }
}

class OneMember {
    public Integer id;
    public String name;
    public OneMember(int id, String name) {
        this.id = id;
        this.name = name;
    }
    public String toString() {
        return ToStringBuilder.reflectionToString(this, ToStringStyle.SHORT_PREFIX_STYLE);
    }

    @Override
    public boolean equals(Object obj) {
        OneMember anotherMember = (OneMember) obj;
        if (this.id == anotherMember.id && this.name.equals(anotherMember.name)) {
            return true;
        }
        return false;
    }
}

class OnePerson {
    public Integer id;
    public String name;

    public OnePerson(int id, String name) {
        this.id = id;
        this.name = name;
    }
    public String toString() {
        return ToStringBuilder.reflectionToString(this, ToStringStyle.SHORT_PREFIX_STYLE);
    }

    @Override
    public boolean equals(Object obj) {
        OnePerson anotherPerson = (OnePerson) obj;
        if (this.id == anotherPerson.id && this.name.equals(anotherPerson.name)) {
            return true;
        }
        return false;
    }
}

위의 코드 중 일부를 Java8 람다 스타일로 변경할 수 있다.

1) Function을 람다 표현식으로 변경

 Function<OneMember, OnePerson> convertFunction = new Function<OneMember, OnePerson>() {
        public OnePerson apply(OneMember member) {
            return new OnePerson(member.id, member.name);
        }
    };

---> 

Function<OneMember, OnePerson> convertFunction = member -> new OnePerson(member.id, member.name);

2) Guava의 ImmutableList를 Streams.of로 변경

ImmutableList<OneMember> immutableMemberList = ImmutableList.of(samuel, daisy, matt);

List<OnePerson> personList = immutableMemberList.stream()
                .map(convertFunction)
                .collect(Collectors.<OnePerson>toList());

--->

List<OnePerson> persons = Stream.of(samuel, daisy, matt)
                              .map(convertFunction)
                              .sorted(comparing(onePerson -> onePerson.id))
                              .collect(toList());