list 根据某个字段分组

Posted 2021-11-22 AresCarry

java8之前List分组
假设有个student类，有id、name、score属性，list集合中存放所有学生信息，现在要根据学生姓名进行分组。

public Map<String, List<Student>> groupList(List<Student> students) {
	Map<String, List<Student>> map = new Hash<>();
	for (Student student : students) {
		List<Student> tmpList = map.get(student.getName());
		if (tmpList == null) {
			tmpList = new ArrayList<>();
			tmpList.add(student);
			map.put(student.getName(), tmpList);
		} else {
			tmpList.add(student);
		}
	}
	return map;
}

java8的List分组

public Map<String, List<Student>> groupList(List<Student> students) {
	Map<String, List<Student>> map = students.stream().collect(Collectors.groupingBy(Student::getName));
	return map;
}