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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naturalOrder Comparator.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; } 