Java字段Stream排序常用方式
這篇博客簡單記錄下 Java 字段 Stream 排序常用方式,歡迎閱讀斧正。
用到的類如下:
public class OrderTest {
private String channelCode;
private BigDecimal rate;
// 省略 getter、setter、toString()、constructor
}準備數(shù)據(jù):
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"));
// 演示給 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);單字段
升序使用 .sorted(Comparator.Comparing(YourClass::Class's Field) 就行,降序使用 .sorted(Comparator.Comparing(YourClass::Class's Field, Comparator.reverseOrder())。
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);
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);輸出:
----------------------------------------------
只按照 channelCode 升序排序:
OrderTest{channelCode='ALL', rate=4.3137}
OrderTest{channelCode='ALL', rate=4.5137}
OrderTest{channelCode='B2C', rate=5.6666}
OrderTest{channelCode='Z04', rate=4.3137}
OrderTest{channelCode='Z09', rate=7.6677}
OrderTest{channelCode='Z09', rate=7.6671}
----------------------------------------------
只按照 channelCode 降序排序:
OrderTest{channelCode='Z09', rate=7.6677}
OrderTest{channelCode='Z09', rate=7.6671}
OrderTest{channelCode='Z04', rate=4.3137}
OrderTest{channelCode='B2C', rate=5.6666}
OrderTest{channelCode='ALL', rate=4.3137}
OrderTest{channelCode='ALL', rate=4.5137}
多字段
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() 的時候要注意排序要求,如果先按照 A 字段升序 B 字段升序的話,使用 reversed() 之后的結果是對 A 降序 B 降序。
不對 null 值處理
先按照 channelCode 升序,再按照 rate 升序排序:
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);輸出:
----------------------------------------------
先按照 channelCode 升序,再按照 rate 升序排序:
OrderTest{channelCode='ALL', rate=4.3137}
OrderTest{channelCode='ALL', rate=4.5137}
OrderTest{channelCode='B2C', rate=5.6666}
OrderTest{channelCode='Z04', rate=4.3137}
OrderTest{channelCode='Z09', rate=7.6671}
OrderTest{channelCode='Z09', rate=7.6677}
先按照 channelCode 升序,再按照 rate 升序排序,使用 reversed():
System.out.println("----------------------------------------------");
System.out.println("先按照 channelCode 升序,再按照 rate 升序排序,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);輸出:
----------------------------------------------
先按照 channelCode 升序,再按照 rate 升序排序,使用 reversed():
OrderTest{channelCode='Z09', rate=7.6677}
OrderTest{channelCode='Z09', rate=7.6671}
OrderTest{channelCode='Z04', rate=4.3137}
OrderTest{channelCode='B2C', rate=5.6666}
OrderTest{channelCode='ALL', rate=4.5137}
OrderTest{channelCode='ALL', rate=4.3137}
先按照 channelCode 升序,再按照 rate 降序排序:
System.out.println("----------------------------------------------");
System.out.println("先按照 channelCode 升序,再按照 rate 降序排序:");
List<OrderTest> channelCodeAscRateDescList =
orderTestList.stream()
.sorted(Comparator.comparing(OrderTest::getChannelCode)
.thenComparing(OrderTest::getRate, Comparator.reverseOrder()))
.collect(Collectors.toList());
channelCodeAscRateDescList.forEach(System.out::println);輸出:
----------------------------------------------
先按照 channelCode 升序,再按照 rate 降序排序:
OrderTest{channelCode='ALL', rate=4.5137}
OrderTest{channelCode='ALL', rate=4.3137}
OrderTest{channelCode='B2C', rate=5.6666}
OrderTest{channelCode='Z04', rate=4.3137}
OrderTest{channelCode='Z09', rate=7.6677}
OrderTest{channelCode='Z09', rate=7.6671}
對 null 值處理
只演示第二個字段,排序方式為倒序,用到了 Comparator.nullsLast(Comparator.reverseOrder()) 以及 Comparator.nullsLast(Comparator.reverseOrder())。
添加對照數(shù)據(jù)
orderTestList.add(z092);
orderTestList.add(B2C1);
orderTestList.add(Z041); 先按照 channelCode 升序,再按照 rate 降序并且 null 值放前面排序:
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);輸出:
----------------------------------------------
先按照 channelCode 升序,再按照 rate 降序并且 null 值放前面排序:
OrderTest{channelCode='ALL', rate=4.5137}
OrderTest{channelCode='ALL', rate=4.3137}
OrderTest{channelCode='B2C', rate=5.6666}
OrderTest{channelCode='B2C', rate=5.6666}
OrderTest{channelCode='Z04', rate=null}
OrderTest{channelCode='Z04', rate=4.3137}
OrderTest{channelCode='Z09', rate=null}
OrderTest{channelCode='Z09', rate=7.6677}
OrderTest{channelCode='Z09', rate=7.6671}
先按照 channelCode 升序,再按照 rate 降序并且 null 值放后面排序:
System.out.println("----------------------------------------------");
System.out.println("先按照 channelCode 升序,再按照 rate 降序并且 null 值放后面排序:");
List<OrderTest> channelCodeAscRateDescNullLastList = orderTestList.stream()
.sorted(Comparator.comparing(OrderTest::getChannelCode)
.thenComparing(OrderTest::getRate, Comparator.nullsLast(Comparator.reverseOrder())))
.collect(Collectors.toList());
channelCodeAscRateDescNullLastList.forEach(System.out::println);輸出:
----------------------------------------------
先按照 channelCode 升序,再按照 rate 降序并且 null 值放后面排序:
OrderTest{channelCode='ALL', rate=4.5137}
OrderTest{channelCode='ALL', rate=4.3137}
OrderTest{channelCode='B2C', rate=5.6666}
OrderTest{channelCode='B2C', rate=5.6666}
OrderTest{channelCode='Z04', rate=4.3137}
OrderTest{channelCode='Z04', rate=null}
OrderTest{channelCode='Z09', rate=7.6677}
OrderTest{channelCode='Z09', rate=7.6671}
OrderTest{channelCode='Z09', rate=null}
總結
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