java8 使用stream进行排序(多字段排序、升序、降序)

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所属分类：Java

文章包含“标题”、“发布时间”、“是否推荐”、“是否置顶”四个属性。

import lombok.AllArgsConstructor;import lombok.Data;import lombok.NoArgsConstructor;@Data@NoArgsConstructor@AllArgsConstructorpublic class Article {
    /**     * 文章标题     */
    private String title;
    /**     * 发布时间     */
    private String releaseTime;
    /**     * 是否推荐：Y 推荐；N 不推荐     */
    private String recommend;
    /**     * 是否置顶: Y 置顶；N 不置顶     */
    private String top;}

测试代码

import java.util.ArrayList;import java.util.Comparator;import java.util.List;import java.util.stream.Collectors;public class Demo {

    public static void main(String[] args) {
        List<Article> list = init();
        sort(list);
        sort2(list);
    }

    /**     * 初始化数据     * @return     */
    private static List<Article> init(){
        List<Article> list = new ArrayList<>();
        list.add(new Article("文章一","2021-11-01","Y","Y"));
        list.add(new Article("文章二","2021-11-02","Y","Y"));
        list.add(new Article("文章三","2021-11-01","Y","N"));
        list.add(new Article("文章一","2021-11-02","Y","N"));
        list.add(new Article("文章一","2021-11-01","N","Y"));
        list.add(new Article("文章一","2021-11-02","N","Y"));
        list.add(new Article("文章一","2021-11-01","N","N"));
        list.add(new Article("文章一","2021-11-02","N","N"));
        return list;
    }
    ....}

排序方法

/**
     * 按照推荐、置顶、发布时间来排序
     * @param list
     */
private static void sort(List<Article> list){
    List<Article> sortList = list.stream()
            // 【X】
            .sorted(Comparator.comparing(Article::getRecommend,Comparator.reverseOrder())
                    // 【Y】
                    .thenComparing(Article::getTop,Comparator.reverseOrder())
                    // 【Z】
                    .thenComparing(Article::getReleaseTime,Comparator.reverseOrder()))
            .collect(Collectors.toList());
    sortList.stream().forEach(System.out::println);
}
//        运行结果：
//        Article(title=文章二, releaseTime=2021-11-02, recommend=Y, top=Y)
//        Article(title=文章一, releaseTime=2021-11-01, recommend=Y, top=Y)
//        Article(title=文章一, releaseTime=2021-11-02, recommend=Y, top=N)
//        Article(title=文章三, releaseTime=2021-11-01, recommend=Y, top=N)
//        Article(title=文章一, releaseTime=2021-11-02, recommend=N, top=Y)
//        Article(title=文章一, releaseTime=2021-11-01, recommend=N, top=Y)
//        Article(title=文章一, releaseTime=2021-11-02, recommend=N, top=N)
//        Article(title=文章一, releaseTime=2021-11-01, recommend=N, top=N)

【X】：优先使用recommend字段排序，并且使用降序排列(Comparator.reverseOrder()),在结果中的体现是前四篇文章的recommend为‘Y’,后四篇的recommend为‘N’
【Y】：之后再使用top字段排序，并且使用降序排列(Comparator.reverseOrder()), 在结果中的体现是recommend相同的文章中，前两篇文章的top为‘Y’, 后两篇文章的top为‘N’
【Z】：最后使用发布时间字段进行排序，并且使用降序排列(Comparator.reverseOrder())

两种倒序方式

Comparator.comparing(类::属性,Comparator.reverseOrder()）

/**
     * 按照推荐、置顶、发布时间来排序
     * @param list
     */
private static void sort(List<Article> list){
    List<Article> sortList = list.stream()
            // 【X】
            .sorted(Comparator.comparing(Article::getRecommend,Comparator.reverseOrder())
                    // 【Y】
                    .thenComparing(Article::getTop,Comparator.reverseOrder())
                    // 【Z】
                    .thenComparing(Article::getReleaseTime,Comparator.reverseOrder()))
            .collect(Collectors.toList());
    sortList.stream().forEach(System.out::println);
}
//        运行结果：
//        Article(title=文章二, releaseTime=2021-11-02, recommend=Y, top=Y)
//        Article(title=文章一, releaseTime=2021-11-01, recommend=Y, top=Y)
//        Article(title=文章一, releaseTime=2021-11-02, recommend=Y, top=N)
//        Article(title=文章三, releaseTime=2021-11-01, recommend=Y, top=N)
//        Article(title=文章一, releaseTime=2021-11-02, recommend=N, top=Y)
//        Article(title=文章一, releaseTime=2021-11-01, recommend=N, top=Y)
//        Article(title=文章一, releaseTime=2021-11-02, recommend=N, top=N)
//        Article(title=文章一, releaseTime=2021-11-01, recommend=N, top=N)

以传入的字段进行倒序排列

【X】：这里就类似于mysql中的 order by recommend desc
【Y】：结合【X】就是order by recommend desc, top desc

Comparator.comparing(Article::getRecommend,Comparator.reverseOrder()).reversed()

private static void sort2(List<Article> list){
    List<Article> sortList = list.stream()
            .sorted(Comparator.comparing(Article::getRecommend,Comparator.reverseOrder())
                    .thenComparing(Article::getTop,Comparator.reverseOrder())
                    .thenComparing(Article::getReleaseTime,Comparator.reverseOrder()).reversed()) // 【X】
            .collect(Collectors.toList());
    sortList.stream().forEach(System.out::println);
}
//        运行结果：
//        Article(title=文章一, releaseTime=2021-11-01, recommend=N, top=N)
//        Article(title=文章一, releaseTime=2021-11-02, recommend=N, top=N)
//        Article(title=文章一, releaseTime=2021-11-01, recommend=N, top=Y)
//        Article(title=文章一, releaseTime=2021-11-02, recommend=N, top=Y)
//        Article(title=文章三, releaseTime=2021-11-01, recommend=Y, top=N)
//        Article(title=文章一, releaseTime=2021-11-02, recommend=Y, top=N)
//        Article(title=文章一, releaseTime=2021-11-01, recommend=Y, top=Y)
//        Article(title=文章二, releaseTime=2021-11-02, recommend=Y, top=Y)