CodeRule Object:

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

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

How to sort this list? Any help?

    @Test
    public void testSort() {
        OrderEntry orderEntry1 = new OrderEntry();
        orderEntry1.setEntryNumber("1");
        OrderEntry orderEntry2 = new OrderEntry();
        orderEntry2.setEntryNumber("2");
        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");
        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");
        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");

        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"},{"entryNumber":"2"},{"entryNumber":"3"},{"entryNumber":"4"},{"giftFlag":1,"sourceEntryNumbers":["1","2"]},{"giftFlag":1,"sourceEntryNumbers":["3"]},{"giftFlag":1,"sourceEntryNumbers":["4"]},{"entryNumber":"8"}]

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