Java 集合按照多字段排序

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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 {@Testpublic 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)));}@Testpublic 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 nullapples.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 nullapples.add(Apple.builder().size(260).build());return apples;}}