OrderEntry Object:

@Data
public static class OrderEntry {
    private String entryNumber;
    // giftFlag=0 means the orderEntry is a normal entry
    // giftFlag=1 means the orderEntry is a gift entry
    private Integer giftFlag;
    private List<String> sourceEntryNumbers;
}

giftFlag=0 means the orderEntry is a normal entry

giftFlag=1 means the orderEntry is a gift entry

I have a list of orderEntry, it contains normal entry and gift entry. Now I want to sort the orderEntry list with specified order, normal entry firstly, if this normal entry have gift entry, then gift entry secondly.

It’s not the multiple fields sort and can not use Comparator’s compare and thenComparing methods

How to sort this list? Any help?

@Test
public void testSort() {
    OrderEntry orderEntry1 = new OrderEntry();
    orderEntry1.setEntryNumber("1");
    orderEntry1.setGiftFlag(0);
    OrderEntry orderEntry2 = new OrderEntry();
    orderEntry2.setEntryNumber("2");
    orderEntry2.setGiftFlag(0);
    OrderEntry orderEntry3 = new OrderEntry();
    orderEntry3.setGiftFlag(1);
    // it means this gift orderEntry created from orderEntry1 and orderEntry2
    orderEntry3.setSourceEntryNumbers(Arrays.asList("1", "2"));

    OrderEntry orderEntry4 = new OrderEntry();
    orderEntry4.setEntryNumber("3");
    orderEntry4.setGiftFlag(0);
    OrderEntry orderEntry5 = new OrderEntry();
    orderEntry5.setGiftFlag(1);
    // it means this gift orderEntry created from orderEntry3
    orderEntry5.setSourceEntryNumbers(Arrays.asList("3"));

    OrderEntry orderEntry6 = new OrderEntry();
    orderEntry6.setEntryNumber("4");
    orderEntry6.setGiftFlag(0);
    OrderEntry orderEntry7 = new OrderEntry();
    orderEntry7.setGiftFlag(1);
    // it means this gift orderEntry created from orderEntry3
    orderEntry7.setSourceEntryNumbers(Arrays.asList("4"));

    OrderEntry orderEntry8 = new OrderEntry();
    orderEntry8.setEntryNumber("8");
    orderEntry8.setGiftFlag(0);

    List<OrderEntry> list = new ArrayList<>();
    list.add(orderEntry1);
    list.add(orderEntry2);
    list.add(orderEntry4);
    list.add(orderEntry6);
    list.add(orderEntry3);
    list.add(orderEntry5);
    list.add(orderEntry7);
    list.add(orderEntry8);

    System.out.println(JSON.toJSONString(list));
    // output:
    // [{"entryNumber":"1","giftFlag":0},{"entryNumber":"2","giftFlag":0},{"entryNumber":"3","giftFlag":0},{"entryNumber":"4","giftFlag":0},{"giftFlag":1,"sourceEntryNumbers":["1","2"]},{"giftFlag":1,"sourceEntryNumbers":["3"]},{"giftFlag":1,"sourceEntryNumbers":["4"]},{"entryNumber":"8","giftFlag":0}]

    // expected output:
    // [{"entryNumber":"1","giftFlag":0},{"entryNumber":"2","giftFlag":0},{"giftFlag":1,"sourceEntryNumbers":["1","2"]},{"entryNumber":"3","giftFlag":0},{"giftFlag":1,"sourceEntryNumbers":["3"]},{"entryNumber":"4","giftFlag":0},{"giftFlag":1,"sourceEntryNumbers":["4"]},{"entryNumber":"8","giftFlag":0}]
}