两个list，高效比对属性相同的不同值

一、实体类

1️⃣源实体类

@Data
public class SouEntity {
    private String id;
    private String name;
    private String deptId;
}

2️⃣目标实体类

@Data
public class TarEntity {
    private String id;
    private String name;
    private String deptId;
}

二、比较方法

1️⃣利用map

private static List<TarEntity> compareFir(List<SouEntity> souList, List<TarEntity> tarList) {
    Map<String, String> map = new HashMap<>(souList.size());
    for (SouEntity sou : souList) {
        map.put(sou.getId(), sou.getDeptId());
    }
    List<TarEntity> differentList = Lists.newArrayList();
    for (TarEntity tar : tarList) {
        String id = tar.getId();
        String deptId = tar.getDeptId();
        if (map.get(id) == null || !deptId.equals(map.get(id))) {
            differentList.add(tar);
        }
    }
    return differentList;
}

2️⃣利用set的不可重复特性

private static Tuple2<List<TarEntity>, List<TarEntity>> compareSec(List<SouEntity> souList, List<TarEntity> tarList) {
    List<TarEntity> existsList = Lists.newArrayList();
    List<TarEntity> unExistsList = Lists.newArrayList();
    Set<String> setKeys = new HashSet<String>();
    for (SouEntity sou : souList) {
        String join = join(sou.getId(), sou.getDeptId());
        setKeys.add(join);
    }
    for (TarEntity tar : tarList) {
        String join = join(tar.getId(), tar.getDeptId());
        if (setKeys.contains(join)) {
            existsList.add(tar);
        } else {
            unExistsList.add(tar);
        }
    }
    return assemble(existsList, unExistsList);
}

public static String join(String... str) {
    for (int i = 0; i < str.length; i++) {
        str[i] = StringUtils.defaultString(str[i]);
    }
    return StringUtils.join(str, "#");
}

public static <T1, T2> Tuple2<T1, T2> assemble(T1 v1, T2 v2) {
    return new Tuple2<T1, T2>(v1, v2);
}

public class Tuple2<T1, T2> {
    private final T1 v1;
    private final T2 v2;

    public T1 v1() {
        return v1;
    }

    public T2 v2() {
        return v2;
    }

    public Tuple2(T1 v1, T2 v2) {
        this.v1 = v1;
        this.v2 = v2;
    }
}

三、测试

public static void main(String[] args) {
    List<SouEntity> souList = new ArrayList<>();
    for (int i = 0; i < 10; i++) {
        SouEntity sou = new SouEntity();
        sou.setId(String.valueOf(i));
        sou.setName(String.valueOf(i));
        sou.setDeptId(String.valueOf(i));
        souList.add(sou);
    }

    List<TarEntity> tarList = new ArrayList<>();
    for (int i = 0; i < 10; i++) {
        TarEntity tar = new TarEntity();
        tar.setId(String.valueOf(i));
        tar.setName(String.valueOf(i));
        tar.setDeptId(String.valueOf(i));
        tarList.add(tar);
    }
    List<TarEntity> tarEntities = compareFir(souList, tarList);
    System.out.println(tarEntities);
    Tuple2<List<TarEntity>, List<TarEntity>> listTuple2 = compareSec(souList, tarList);
    System.out.println(listTuple2.v1());
    System.out.println(listTuple2.v2());
}

结果如下：

[]
[TarEntity(id=0, name=0, deptId=0), TarEntity(id=1, name=1, deptId=1), TarEntity(id=2, name=2, deptId=2), TarEntity(id=3, name=3, deptId=3), TarEntity(id=4, name=4, deptId=4), TarEntity(id=5, name=5, deptId=5), TarEntity(id=6, name=6, deptId=6), TarEntity(id=7, name=7, deptId=7), TarEntity(id=8, name=8, deptId=8), TarEntity(id=9, name=9, deptId=9)]
[]

四、总结

利用 map 需要考虑 key 值的唯一性，如果 key 有重复，则不适合，建议采用第二种方法。