Java中 List 集合，通过 Stream 流进行排序总结

一、数据准备

public class OrderTest {private String channelCode;private BigDecimal rate;// 省略 getter、setter、toString()、constructor
}

		List<OrderTest> orderTestList = new ArrayList<>();OrderTest z09 = new OrderTest("Z09", new BigDecimal("7.6677"));OrderTest B2C = new OrderTest("B2C", new BigDecimal("5.6666"));OrderTest Z04 = new OrderTest("Z04", new BigDecimal("4.3137"));OrderTest ALL = new OrderTest("ALL", new BigDecimal("4.3137"));OrderTest ALL1 = new OrderTest("ALL", new BigDecimal("4.5137"));// 演示多字段排序使用OrderTest z091 = new OrderTest("Z09", new BigDecimal("7.6671"));// 演示给 null 值排序用OrderTest z092 = new OrderTest("Z09", null);OrderTest B2C1 = new OrderTest("B2C", new BigDecimal("5.6666"));OrderTest Z041 = new OrderTest("Z04", null);orderTestList.add(z09);orderTestList.add(z091);orderTestList.add(B2C);orderTestList.add(Z04);orderTestList.add(ALL);orderTestList.add(ALL1);

二、单字段排序

2.1、升序

 list.stram().sorted(Comparator.Comparing(YourClass::Class's Field)

System.out.println("----------------------------------------------");System.out.println("只按照 channelCode 升序排序：");List<OrderTest> channelAsc =orderTestList.stream().sorted(Comparator.comparing(OrderTest::getChannelCode)).collect(Collectors.toList());channelAsc.forEach(System.out::println);

结果：

2.2、降序

 list.stram().sorted(Comparator.Comparing(YourClass::Class's Field, Comparator.reverseOrder())

System.out.println("----------------------------------------------");System.out.println("只按照 channelCode 降序排序：");List<OrderTest> channelDesc =orderTestList.stream().sorted(Comparator.comparing(OrderTest::getChannelCode, Comparator.reverseOrder())).collect(Collectors.toList());channelDesc.forEach(System.out::println);

结果：

二、多字段排序

利用的是 thenComparing()：
升序 thenComparing(YourClass::Class's Field)，
降序 thenComparing(YourClass::Class's Field, Comparator.reverseOrder())。注意： 使用 thenComparing(YourClass::Class's Field).reversed() 的时候要注意排序要求，
如果先按照 A 字段升序 B 字段升序的话，使用 reversed() 之后的结果是对 A 降序 B 降序。

System.out.println("----------------------------------------------");System.out.println("先按照 channelCode 升序，再按照 rate 升序排序：");List<OrderTest> channelCodeAscRateAscList =orderTestList.stream().sorted(Comparator.comparing(OrderTest::getChannelCode).thenComparing(OrderTest::getRate)).collect(Collectors.toList());channelCodeAscRateAscList.forEach(System.out::println);

结果

先按照 channelCode 将序，再按照 rate 升序将序，使用 reversed()：

System.out.println("----------------------------------------------");System.out.println("先按照 channelCode 将序，再按照 rate 将序排序，使用 reversed()：");List<OrderTest> channelCodeAscRateAscWithReversedList =orderTestList.stream().sorted(Comparator.comparing(OrderTest::getChannelCode).thenComparing(OrderTest::getRate).reversed()).collect(Collectors.toList());channelCodeAscRateAscWithReversedList.forEach(System.out::println);

结果

三、对 null 值处理

 Comparator.nullsFirst(Comparator.reverseOrder())  -- null排在前面，reverseOrder是倒序，升序用naturalOrderComparator.nullsLast(Comparator.reverseOrder())   -- null排在后面，reverseOrder是倒序，升序用naturalOrder

orderTestList.add(new OrderTest(("Z09")));orderTestList.add(new OrderTest(("B2C")));orderTestList.add(new OrderTest(("Z04")));System.out.println("----------------------------------------------");System.out.println("先按照 channelCode 升序，再按照 rate 降序并且 null 值放前面排序：");List<OrderTest> channelCodeAscRateDescNullFirstList = orderTestList.stream().sorted(Comparator.comparing(OrderTest::getChannelCode).thenComparing(OrderTest::getRate, Comparator.nullsFirst(Comparator.reverseOrder()))).collect(Collectors.toList());channelCodeAscRateDescNullFirstList.forEach(System.out::println);

结果

四、对排序字段个数不固定的情况，如何排序

需求：排序字段个数不确定，如何实现动态排序？

伪代码示例：

		Comparator<SurgUnArrangeResponse> comparing = null;for (int i = 0; i < dictItemList.size(); i++) {String cd = dictItemList.get(i).getCd();if (i == 0) {// 首次排序comparing = getComparingByDictCd(cd, null);} else {// 第二次排序及以上comparing = getComparingByDictCd(cd, comparing);}}// comparing 比较器，保存了排序的规则，responseList 是被排序的集合responseList = responseList.stream().sorted(comparing).collect(Collectors.toList());// getComparingByDictCd 方法private Comparator<SurgUnArrangeResponse> getComparingByDictCd(String dictCd, 
Comparator<SurgUnArrangeResponse> result = null;switch (dictCd) {case "age":result = comparing == null ? Comparator.comparing(SurgUnArrangeResponse::getAge, Comparator.nullsLast(Comparator.reverseOrder())) :comparing.thenComparing(SurgUnArrangeResponse::getAge, Comparator.nullsLast(Comparator.reverseOrder()));break;....}return result;}