Java8 - Collections.groupingBy()分组

旧城等待， 2023-09-28 20:49 76阅读 0赞

### 1、Collections.groupingBy() 单字段分组 ###

@ToString
    @Data
    @AllArgsConstructor
    public class People {
        
    
        private Integer id;
        private String name;
        private String address;
        private Integer age;
    }

测试类

public static void main(String[] args) {
        
            People people1 = new People(1, "only-qi1", "11", 11);
            People people2 = new People(2, "only-qi2", "12", 12);
            People people3 = new People(3, "only-qi3", "14", 13);
            People people4 = new People(1, "only-qi4", "14", 14);
            People people5 = new People(2, "only-qi5", "13", 15);
            People people6 = new People(1, "only-qi6", "11", 11);
            ArrayList<People> arrayList = new ArrayList<>();
            arrayList.add(people1);
            arrayList.add(people2);
            arrayList.add(people3);
            arrayList.add(people4);
            arrayList.add(people5);
            arrayList.add(people6);
            
            Map<String, List<People>> map = arrayList.stream().collect(Collectors.groupingBy(People::getAddress));
            for (String s : map.keySet()) {
        
                System.out.println("key值是：" + s + "=========" + "value的值是" + map.get(s));
            }
        }

测试结果：  
![在这里插入图片描述][869a3dee9f3d4a02b9c9c8ad53eba964.png]

#### 2、Collections.groupingBy() 多字段分组 ####

Map<String, List<People>> map1 = arrayList.stream().collect(Collectors.groupingBy(p->p.getAddress()+"#"+p.getAge()));
            for (String s : map1.keySet()) {
        
                System.out.println("key值是：" + s + "=========" + "value的值是" + map1.get(s));
            }

测试结果：  
![在这里插入图片描述][e1dc40e128834ad0b16c8bb18912bafb.png]

[869a3dee9f3d4a02b9c9c8ad53eba964.png]: https://img-blog.csdnimg.cn/869a3dee9f3d4a02b9c9c8ad53eba964.png
[e1dc40e128834ad0b16c8bb18912bafb.png]: https://img-blog.csdnimg.cn/e1dc40e128834ad0b16c8bb18912bafb.png