hutool工具-----CollStreamUtil

忘是亡心i 2023-09-30 08:42 4阅读 0赞

### 文章预览： ###

*  介绍
 *  使用
 *   *  一、集合转Map
     *   *  1. 建立一个学生id和学生对象之间的map：
         *  2.自定义Map的key和value放的内容
     *  二、分组
     *   *  1. 按照班级分组
         *  2、将collection按照两个规则(比如有相同的年级id,班级id)分组成双层map（集合map）
         *  3、将collection按照两个规则(比如有相同的年级id,班级id)分组成双层map（单对象map）
         *  4.作为所有groupingBy的公共方法，更接近于原生，灵活性更强
     *  三、转换提取

[本篇博客来自hutool][hutool]

[Java8中Collectors详解][Java8_Collectors]

# 介绍 #

Java8中的新特性之一就是Stream，Hutool针对常用操作做了一些封装，本文将stream中collection和hutool工具类做了对比，同样的功能封装后是多么的简洁，之前本人都是手写工具，现在知道hutool还有这种功能，这用起来简直绝了

# 使用 #

Student

@Data
    @NoArgsConstructor
    @AllArgsConstructor
    @ToString
    public  class Student {
        
        private long termId;//学期id
        private long gradeId;//年级id
        private long classId;//班级id
        private long studentId;//学生id
        private String name;//学生名称
    
        public Student(long termId, long classId, long studentId, String name) {
        
            this.termId = termId;
            this.classId = classId;
            this.studentId = studentId;
            this.name = name;
        }
    }

## 一、集合转Map ##

### 1. 建立一个学生id和学生对象之间的map： ###

@Test
        void toIdentityMapTest() {
        
            List<Student> list = new ArrayList<>();
            list.add(new Student(1, 1, 1, "张三"));
            list.add(new Student(1, 1, 2, "李四"));
            list.add(new Student(1, 1, 3, "王五"));
            //手写方法
            Map<Long, Student> collect = list.stream().collect(Collectors.toMap(Student::getStudentId, s -> s));
    
            //使用封装的工具
            Map<Long, Student> map = CollStreamUtil.toIdentityMap(list, Student::getStudentId);
    
        }

结果  
手写方法  
![在这里插入图片描述][watermark_type_d3F5LXplbmhlaQ_shadow_50_text_Q1NETiBA5LyP5Yqg54m56YGH5LiK6KW_5p-a_size_20_color_FFFFFF_t_70_g_se_x_16]  
hutool工具  
![在这里插入图片描述][watermark_type_d3F5LXplbmhlaQ_shadow_50_text_Q1NETiBA5LyP5Yqg54m56YGH5LiK6KW_5p-a_size_20_color_FFFFFF_t_70_g_se_x_16 1]

### 2.自定义Map的key和value放的内容 ###

如我们可以将学生信息的id和姓名生成map：

@Test
        void toMapTest() {
        
            List<Student> list = new ArrayList<>();
            list.add(new Student(1, 1, 1, "张三"));
            list.add(new Student(1, 1, 2, "李四"));
            list.add(new Student(1, 1, 3, "王五"));
            //手写方法
            Map<Long, String> collect = list.stream()
                    .collect(Collectors.toMap(student -> student.getStudentId(),
                            Student::getName, (s1, s2) -> s2));
    
            //使用封装的工具
            Map<Long, String> map2 = CollStreamUtil.toMap(list, Student::getStudentId, Student::getName);
    
            System.out.println("map2 = " + map2);
    
        }

结果  
手写方法  
![在这里插入图片描述][watermark_type_d3F5LXplbmhlaQ_shadow_50_text_Q1NETiBA5LyP5Yqg54m56YGH5LiK6KW_5p-a_size_20_color_FFFFFF_t_70_g_se_x_16 2]  
工具  
![在这里插入图片描述][watermark_type_d3F5LXplbmhlaQ_shadow_50_text_Q1NETiBA5LyP5Yqg54m56YGH5LiK6KW_5p-a_size_20_color_FFFFFF_t_70_g_se_x_16 3]

## 二、分组 ##

### 1. 按照班级分组 ###

@Test
        void groupByKeyTest() {
        
            List<Student> list = new ArrayList<>();
            list.add(new Student(1, 1, 1, "张三"));
            list.add(new Student(1, 2, 2, "李四"));
            list.add(new Student(2, 1, 1, "擎天柱"));
            list.add(new Student(2, 2, 2, "威震天"));
            list.add(new Student(2, 3, 2, "霸天虎"));
            //手写方法
            Map<Long, List<Student>> collect = list.stream().collect(Collectors.groupingBy(Student::getClassId));
    
            //使用封装的工具
            Map<Long, List<Student>> map = CollStreamUtil.groupByKey(list, Student::getClassId);
            System.out.println("map = " + map);
        }

结果  
手写方法  
![在这里插入图片描述][watermark_type_d3F5LXplbmhlaQ_shadow_50_text_Q1NETiBA5LyP5Yqg54m56YGH5LiK6KW_5p-a_size_20_color_FFFFFF_t_70_g_se_x_16 4]  
使用工具  
![在这里插入图片描述][watermark_type_d3F5LXplbmhlaQ_shadow_50_text_Q1NETiBA5LyP5Yqg54m56YGH5LiK6KW_5p-a_size_20_color_FFFFFF_t_70_g_se_x_16 5]

### 2、将collection按照两个规则(比如有相同的年级id,班级id)分组成双层map（集合map） ###

第二层value是集合，将符合条件的数据放入集合中

//将collection按照两个规则(比如有相同的年级id,班级id)分组成双层map
        @Test
        void groupBy2Key() {
        
            //将集合先按照年级分组，年级相同再按照班级分组
            List<Student> list = new ArrayList<>();
            list.add(new Student(1, 1,1, 1, "张三"));
            list.add(new Student(1, 1,1, 2, "李四"));
            list.add(new Student(1, 2,1, 3, "王五"));
            list.add(new Student(1, 2,1, 3, "王流"));
            list.add(new Student(1, 2, 2, 3, "汪一"));
            list.add(new Student(1, 2, 2, 3, "汪二"));
            //同年级，同班级的学生放入集合中
            Map<Long, Map<Long, List<Student>>> longMapMap = list.stream().collect(Collectors.groupingBy(Student::getGradeId, Collectors.groupingBy(Student::getClassId)));
            Map<Long, Map<Long, List<Student>>> longMapMap1 = CollStreamUtil.groupBy2Key(list, Student::getGradeId, Student::getClassId);
    
            //同年级，同班级的学生按照","拼接
            Map<Long, Map<Long, String>> sameGradeAndClassStudentMap = list.stream()
                            .collect(Collectors.groupingBy(Student::getGradeId,
                                                            Collectors.groupingBy(Student::getClassId, Collectors.mapping(Student::getName, Collectors.joining(",")))));
    
            //同年级，同班级的学生姓名放入集合中
            Map<Long, Map<Long, List<String>>> sameGradeAndClassStudentListMap = list.stream()
                    .collect(Collectors.groupingBy(Student::getGradeId, Collectors.groupingBy(Student::getClassId, Collectors.mapping(Student::getName, Collectors.toList()))));
    
            Map<Long, Map<Long, Student>> longMapMap2 = CollStreamUtil.group2Map(list, Student::getGradeId, Student::getClassId);
            System.out.println("longMapMap = " + longMapMap);
        }    //将collection按照两个规则(比如有相同的年级id,班级id)分组成双层map

**同年级，同班级的学生放入集合中 longMapMap结果**  
![在这里插入图片描述][watermark_type_d3F5LXplbmhlaQ_shadow_50_text_Q1NETiBA5LyP5Yqg54m56YGH5LiK6KW_5p-a_size_20_color_FFFFFF_t_70_g_se_x_16 6]  
**同年级，同班级的学生姓名按照","拼接 sameGradeAndClassStudentNameMap结果**

![在这里插入图片描述][c7c2fe46b9cf4df697fa0a16125deea4.png]

**同年级，同班级的学生姓名放入集合中结果**  
![在这里插入图片描述][be6861c5a16c4bc4889b609b5fd44228.png]

### 3、将collection按照两个规则(比如有相同的年级id,班级id)分组成双层map（单对象map） ###

@Test
        void group2Map() {
        
            List<Student> list = new ArrayList<>();
            list.add(new Student(1, 1, 1, 1, "张三"));
            list.add(new Student(1, 1, 1, 2, "李四"));
            list.add(new Student(1, 2, 1, 3, "王五"));
            list.add(new Student(1, 2, 1, 3, "王流"));
            list.add(new Student(1, 2, 2, 3, "汪一"));
            list.add(new Student(1, 2, 2, 3, "汪二"));
            Map<Long, Map<Long, Student>> longMapMap1 = CollStreamUtil.group2Map(list, Student::getGradeId, Student::getClassId);
        }

结果  
![在这里插入图片描述][watermark_type_d3F5LXplbmhlaQ_shadow_50_text_Q1NETiBA5LyP5Yqg54m56YGH5LiK6KW_5p-a_size_20_color_FFFFFF_t_70_g_se_x_16 7]

### 4.作为所有groupingBy的公共方法，更接近于原生，灵活性更强 ###

@Test
        void groupBy() {
        
            List<Student> list = new ArrayList<>();
            list.add(new Student(1, 1, 1, "张三"));
            list.add(new Student(1, 1, 2, "李四"));
            list.add(new Student(1, 2, 3, "王五"));
            //手动
            Map<Long, Long> collect = list.stream()
                    .collect(Collectors.groupingBy(Student::getClassId, Collectors.counting()));
    
            //统计每个班的人数
            Map<Long, Long> longLongMap = CollStreamUtil.groupBy(list, Student::getClassId, Collectors.counting());
            System.out.println("longMapMap = " + longLongMap);
        }

结果  
![在这里插入图片描述][watermark_type_d3F5LXplbmhlaQ_shadow_50_text_Q1NETiBA5LyP5Yqg54m56YGH5LiK6KW_5p-a_size_20_color_FFFFFF_t_70_g_se_x_16 8]

## 三、转换提取 ##

我们可以将学生信息列表转换提取为姓名的列表：

@Test
        void toList() {
        
            List<Student> list = new ArrayList<>();
            list.add(new Student(1, 1, 1, "张三"));
            list.add(new Student(1, 1, 2, "李四"));
            list.add(new Student(1, 1, 3, "王五"));
            List<String> list2 = CollStreamUtil.toList(list, Student::getName);
        }

结果  
![在这里插入图片描述][watermark_type_d3F5LXplbmhlaQ_shadow_50_text_Q1NETiBA5LyP5Yqg54m56YGH5LiK6KW_5p-a_size_20_color_FFFFFF_t_70_g_se_x_16 9]

[hutool]: https://www.hutool.cn/docs/#/core/%E9%9B%86%E5%90%88%E7%B1%BB/%E9%9B%86%E5%90%88%E4%B8%B2%E8%A1%8C%E6%B5%81%E5%B7%A5%E5%85%B7-CollStreamUtil
[Java8_Collectors]: https://blog.csdn.net/qq_43842093/article/details/122136492
[watermark_type_d3F5LXplbmhlaQ_shadow_50_text_Q1NETiBA5LyP5Yqg54m56YGH5LiK6KW_5p-a_size_20_color_FFFFFF_t_70_g_se_x_16]: https://img-blog.csdnimg.cn/3e8bd3fd06784df29f8db8ec1a8bea3e.png?x-oss-process=image/watermark,type_d3F5LXplbmhlaQ,shadow_50,text_Q1NETiBA5LyP5Yqg54m56YGH5LiK6KW_5p-a,size_20,color_FFFFFF,t_70,g_se,x_16
[watermark_type_d3F5LXplbmhlaQ_shadow_50_text_Q1NETiBA5LyP5Yqg54m56YGH5LiK6KW_5p-a_size_20_color_FFFFFF_t_70_g_se_x_16 1]: https://img-blog.csdnimg.cn/2485cf1ff480463185ec71c0ee957f56.png?x-oss-process=image/watermark,type_d3F5LXplbmhlaQ,shadow_50,text_Q1NETiBA5LyP5Yqg54m56YGH5LiK6KW_5p-a,size_20,color_FFFFFF,t_70,g_se,x_16
[watermark_type_d3F5LXplbmhlaQ_shadow_50_text_Q1NETiBA5LyP5Yqg54m56YGH5LiK6KW_5p-a_size_20_color_FFFFFF_t_70_g_se_x_16 2]: https://img-blog.csdnimg.cn/34fc14ba7a18486ea00c87290a8558f2.png?x-oss-process=image/watermark,type_d3F5LXplbmhlaQ,shadow_50,text_Q1NETiBA5LyP5Yqg54m56YGH5LiK6KW_5p-a,size_20,color_FFFFFF,t_70,g_se,x_16
[watermark_type_d3F5LXplbmhlaQ_shadow_50_text_Q1NETiBA5LyP5Yqg54m56YGH5LiK6KW_5p-a_size_20_color_FFFFFF_t_70_g_se_x_16 3]: https://img-blog.csdnimg.cn/1dc6a239fba4457db15c5c7cf5cd73d6.png?x-oss-process=image/watermark,type_d3F5LXplbmhlaQ,shadow_50,text_Q1NETiBA5LyP5Yqg54m56YGH5LiK6KW_5p-a,size_20,color_FFFFFF,t_70,g_se,x_16
[watermark_type_d3F5LXplbmhlaQ_shadow_50_text_Q1NETiBA5LyP5Yqg54m56YGH5LiK6KW_5p-a_size_20_color_FFFFFF_t_70_g_se_x_16 4]: https://img-blog.csdnimg.cn/f9b67dc032c64d189bafbf2e65821bb6.png?x-oss-process=image/watermark,type_d3F5LXplbmhlaQ,shadow_50,text_Q1NETiBA5LyP5Yqg54m56YGH5LiK6KW_5p-a,size_20,color_FFFFFF,t_70,g_se,x_16
[watermark_type_d3F5LXplbmhlaQ_shadow_50_text_Q1NETiBA5LyP5Yqg54m56YGH5LiK6KW_5p-a_size_20_color_FFFFFF_t_70_g_se_x_16 5]: https://img-blog.csdnimg.cn/8695b43dd56844c3a0baa8e6a5cc6bdb.png?x-oss-process=image/watermark,type_d3F5LXplbmhlaQ,shadow_50,text_Q1NETiBA5LyP5Yqg54m56YGH5LiK6KW_5p-a,size_20,color_FFFFFF,t_70,g_se,x_16
[watermark_type_d3F5LXplbmhlaQ_shadow_50_text_Q1NETiBA5LyP5Yqg54m56YGH5LiK6KW_5p-a_size_20_color_FFFFFF_t_70_g_se_x_16 6]: https://img-blog.csdnimg.cn/827075367c0c4c91ae66e46b9e5abdfb.png?x-oss-process=image/watermark,type_d3F5LXplbmhlaQ,shadow_50,text_Q1NETiBA5LyP5Yqg54m56YGH5LiK6KW_5p-a,size_20,color_FFFFFF,t_70,g_se,x_16
[c7c2fe46b9cf4df697fa0a16125deea4.png]: https://img-blog.csdnimg.cn/c7c2fe46b9cf4df697fa0a16125deea4.png
[be6861c5a16c4bc4889b609b5fd44228.png]: https://img-blog.csdnimg.cn/be6861c5a16c4bc4889b609b5fd44228.png
[watermark_type_d3F5LXplbmhlaQ_shadow_50_text_Q1NETiBA5LyP5Yqg54m56YGH5LiK6KW_5p-a_size_20_color_FFFFFF_t_70_g_se_x_16 7]: https://img-blog.csdnimg.cn/ee263b5dac5742d684e2d3d62d319974.png?x-oss-process=image/watermark,type_d3F5LXplbmhlaQ,shadow_50,text_Q1NETiBA5LyP5Yqg54m56YGH5LiK6KW_5p-a,size_20,color_FFFFFF,t_70,g_se,x_16
[watermark_type_d3F5LXplbmhlaQ_shadow_50_text_Q1NETiBA5LyP5Yqg54m56YGH5LiK6KW_5p-a_size_20_color_FFFFFF_t_70_g_se_x_16 8]: https://img-blog.csdnimg.cn/a005e87b0c674076a7ba8d0f0df5f6a5.png?x-oss-process=image/watermark,type_d3F5LXplbmhlaQ,shadow_50,text_Q1NETiBA5LyP5Yqg54m56YGH5LiK6KW_5p-a,size_20,color_FFFFFF,t_70,g_se,x_16
[watermark_type_d3F5LXplbmhlaQ_shadow_50_text_Q1NETiBA5LyP5Yqg54m56YGH5LiK6KW_5p-a_size_20_color_FFFFFF_t_70_g_se_x_16 9]: https://img-blog.csdnimg.cn/7307c0e4e21c4b2d857bb6064676f912.png?x-oss-process=image/watermark,type_d3F5LXplbmhlaQ,shadow_50,text_Q1NETiBA5LyP5Yqg54m56YGH5LiK6KW_5p-a,size_20,color_FFFFFF,t_70,g_se,x_16