Java 集合按照多字段排序

以你之姓@ 2022-11-24 14:27 225阅读 0赞

> 以 Apple 实体为例，先按 name 升序排序，再按 size 降序排序

## 测试代码 ##

### Apple 类 ###

package com.me.entity;
    
    import lombok.Builder;
    import lombok.Data;
    
    /** * @author yanyg * @since 2020/8/5 */
    @Data
    @Builder
    public class Apple { 
        private String color;
        private String name;
        private Integer size;
    
    }

### AppleComparatorTest 类 ###

package cn.me.mybatis;
    
    import cn.yto.utils.JsonUtil;
    import com.me.entity.Apple;
    import org.assertj.core.util.Lists;
    import org.junit.Test;
    import org.junit.runner.RunWith;
    import org.springframework.boot.test.context.SpringBootTest;
    import org.springframework.test.context.junit4.SpringRunner;
    
    import java.util.Comparator;
    import java.util.List;
    
    /** * @author yanyg * @since 2020/8/5 */
    @RunWith(SpringRunner.class)
    @SpringBootTest(classes = SpringBootTest.class)
    public class AppleComparatorTest { 
    
        @Test
        public void comparatorApples() { 
            List<Apple> apples = buildApples();
    
            Comparator<Apple> byName = Comparator.comparing(Apple::getName);
            Comparator<Apple> bySizeDesc = Comparator.comparing(Apple::getSize).reversed();
            /** * 先按 name 升序排序，再按 size 降序排序， 但是 name 和 size 都不能为 null */
            apples.sort(byName.thenComparing(bySizeDesc));
            apples.stream().forEach(t -> System.out.println(JsonUtil.toJson(t)));
        }
    
        @Test
        public void comparatorApplesTwo() { 
            List<Apple> apples = buildApples();
            // name 为 null 时，排在最后面
            Comparator<Apple> byName = 
            	Comparator.comparing(apple -> apple.getName(), Comparator.nullsLast(String::compareTo));
            // size 为 null 时，排在最后面
            Comparator<Apple> bySizeDesc = 
            	Comparator.comparing(apple -> apple.getSize(),Comparator.nullsFirst(Integer::compareTo).reversed());
    
            /** * 先按 name 升序排序，再按 size 降序排序， name 和 size 可为 null */
            apples.sort(byName.thenComparing(bySizeDesc));
            // since 1.8
            //apples = apples.stream().sorted(byName.thenComparing(bySizeDesc)).collect(Collectors.toList());
            apples.stream().forEach(t -> System.out.println(JsonUtil.toJson(t)));
        }
    
    
        public List<Apple> buildApples() { 
            List<Apple> apples = Lists.newArrayList();
            apples.add(Apple.builder().name("red apple").size(180).build());
            apples.add(Apple.builder().name("red apple").size(150).build());
            // size 为 null
            apples.add(Apple.builder().name("red apple").build());
            apples.add(Apple.builder().name("big apple").size(260).build());
            apples.add(Apple.builder().name("small apple").size(150).build());
            apples.add(Apple.builder().name("big apple").size(300).build());
            apples.add(Apple.builder().name("green apple").size(310).build());
            // name 为 null
            apples.add(Apple.builder().size(260).build());
            return apples;
        }
    
    }

## 参考文档 ##

*  [java list 按照多字段排序][java list]

[java list]: https://www.cnblogs.com/wanglg629/p/10638954.html