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
Comparator.nullsLast(Comparator.reverseOrder()) -- null排在后面
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