Collectors.groupingBy妙用

赵哥窟

发布于 2022-07-28 05:42:01

65300

代码可运行

文章被收录于专栏：日常技术分享日常技术分享

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代码可运行

Collectors.groupingBy根据一个或多个属性对集合中的项目进行分组

@Data
public class Student {
    private String name;
    private String sex;
    private int age;
    private String className;

    public Student(String name,String sex,int age,String className){
        this.name = name;
        this.sex = sex;
        this.age = age;
        this.className = className;
    }
}

按照性别分组

public static void main(String[] args) {
        Student student1 = new Student("张三","1",10,"三班");
        Student student2 = new Student("张三","1",11,"三班");
        Student student3 = new Student("李四","0",12,"三班");
        Student student4 = new Student("王二","0",12,"三班");
        Student student5 = new Student("麻子","0",11,"三班");
        List<Student> studentList = Lists.newArrayList(student1, student2, student3, student4, student5);

        Map<Object, List<Student>> newList = studentList.stream().collect(Collectors.groupingBy(student -> student.getSex()));
        log.info(newList.toString());
    }

也可以多个属性分组,按照性别和班级

public static void main(String[] args) {
         Student student1 = new Student("张三","1",10,"三班");
        Student student2 = new Student("张三","1",11,"三班");
        Student student3 = new Student("李四","0",12,"三班");
        Student student4 = new Student("王二","0",12,"三班");
        Student student5 = new Student("麻子","0",11,"三班");
        List<Student> studentList = Lists.newArrayList(student1, student2, student3, student4, student5);

        Map<Object, List<Student>> newList = studentList.stream().collect(Collectors.groupingBy(student -> student.getName() + ":" + student.getSex()+ ":" + student.getAge()));
        log.info(newList.toString());

    }

另外一个用法就是判断入参数组里面是否有重复数据这个时候就可以用

 long distinctCount = studentList.stream().collect(Collectors.groupingBy(student -> student.getName() + ":" + student.getSex()+ ":" + student.getAge()));
  if (paramList.size() != distinctCount) {
            throw new BizException("xxxxxx重复");
  }