Listを指定サイズ毎に分割するutility

CollectionUtils.java

import java.util.Collections;
import java.util.List;
import java.util.stream.Collectors;
import java.util.stream.IntStream;

public class CollectionUtils {

    /**
     * Listを指定したサイズ毎に分割します。
     *
     * @param origin 分割元のList
     * @param size   Listの分割単位
     * @return サイズ毎に分割されたList。但し、Listがnullまたは空の場合、もしくはsizeが0以下の場合は空のListを返す。
     */
    public static <T> List<List<T>> divide(List<T> origin, int size) {
        if (origin == null || origin.isEmpty() || size <= 0) {
            return Collections.emptyList();
        }

        int block = origin.size() / size + (origin.size() % size > 0 ? 1 : 0);

        return IntStream.range(0, block)
                .boxed()
                .map(i -> {
                    int start = i * size;
                    int end = Math.min(start + size, origin.size());
                    return origin.subList(start, end);
                })
                .collect(Collectors.toList());
    }

}

CollectionUtilsTest.java

import org.junit.Test;
import org.junit.runner.RunWith;
import org.junit.runners.JUnit4;

import static java.util.Arrays.asList;
import static java.util.Collections.emptyList;
import static org.hamcrest.CoreMatchers.is;
import static org.junit.Assert.assertThat;

@RunWith(JUnit4.class)
public class CollectionUtilsTest {

    @Test
    public void testDivide() {
        assertThat(
                CollectionUtils.divide(null, 3),
                is(emptyList()));
        assertThat(
                CollectionUtils.divide(emptyList(), 3),
                is(emptyList()));
        assertThat(
                CollectionUtils.divide(
                        asList(1, 2, 3),
                        0
                ),
                is(emptyList()));
        assertThat(
                CollectionUtils.divide(
                        asList(1),
                        1
                ),
                is(asList(
                        asList(1)
                )));
        assertThat(
                CollectionUtils.divide(
                        asList(1, 2, 3, 4, 5, 6, 7, 8, 9, 10),
                        3
                ),
                is(asList(
                        asList(1, 2, 3),
                        asList(4, 5, 6),
                        asList(7, 8, 9),
                        asList(10)
                )));
    }

}