一、数据准备

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

		List 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 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 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 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 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 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 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 getComparingByDictCd(String dictCd,  Comparator 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; 		}