Java8实现Stream流的合并的方法展示

@Data
@AllArgsConstructor
public class Customer {
    private String name;
    private String id1;
    private String id2;
    private String id3;
}

customerList.stream().map(Customer::getId1).filter(Objects::nonNull).collect(Collectors.toList())

Stream<String> concat = Stream.concat(customerList.stream().map(Customer::getId1),
		customerList.stream().map(Customer::getId2));
List<String> ids = Stream.concat(concat, customerList.stream().map(Customer::getId3))
        .filter(Objects::nonNull)
        .collect(Collectors.toList());

List<String> ids = Stream.of(customerList.stream().map(Customer::getId1),
                             customerList.stream().map(Customer::getId2),
                             customerList.stream().map(Customer::getId3))
        .flatMap(idStream -> idStream)
        .filter(Objects::nonNull)
        .collect(Collectors.toList());