记录java常用方法

1.取两个集合的差集
java 复制代码
public class StreamApiTest {

    public static void main(String[] args) {
        List<MktCamCustDetail> batchPos = Arrays.asList(
                new MktCamCustDetail("123456", 123456L, "张三"),
                new MktCamCustDetail("345678", 345678L, "王五"),
                new MktCamCustDetail("234567", 234567L, "赵六"),
                new MktCamCustDetail("123456", 123456L, "张三"));
        // 从 batchPos 中提取 objId 列表，去重后直接用于查询
        List<MktCamCustDetail> mktCamCustDetailList = Optional.ofNullable(batchPos)
                .orElse(Collections.emptyList()) // 防止 batchPos 为 null
                .stream()
                .map(MktCamCustDetail::getObjId)
                .filter(Objects::nonNull) // 避免包含 null 的 objId
                .distinct()
                .collect(Collectors.collectingAndThen(Collectors.toList(), StreamApiTest::getMktCamCustDetails));

        // 取读取到的数据与数据库中已存在的资产的差集，即新增的资产
        List<MktCamCustDetail> newMktCamCustDetailList = batchPos.stream()
                .filter(m -> mktCamCustDetailList.stream().noneMatch(m2 -> m2.getObjId().equals(m.getObjId())))
                .collect(Collectors.toList());
        System.out.println(newMktCamCustDetailList);
    }

    /**
     * 根据 objIdList 查询 MktCamCustDetail 列表
     *
     * @param objIdList
     * @return
     */
    public static List<MktCamCustDetail> getMktCamCustDetails(List<String> objIdList) {
        List<MktCamCustDetail> list = Arrays.asList(
                new MktCamCustDetail("123456", 123456L, "张三"),
                new MktCamCustDetail("345678", 345678L, "王五"),
                // new MktCamCustDetail("234567", 234567L, "赵六"),
                new MktCamCustDetail("123456", 123456L, "张三")
        );
        // 如果 objIdList 为空，直接返回空列表，避免不必要的查询
        return list;
    }
}

/**
 * MktCamCustDetail 实体类
 */
@Data
@Builder
@NoArgsConstructor
@AllArgsConstructor
class MktCamCustDetail {
    private String objId;
    private Long custId;
    private String custName;
}