java8 List轉Map常用操作

public class Java8Demo {
    public static void main(String[] args) {
        List<Student> studentList = Lists.newArrayList();
        studentList.add(new Student(1, "張三", 10, "浙江杭州"));
        studentList.add(new Student(2, "李四", 12, "江蘇南京"));
        studentList.add(new Student(3, "王五", 15, "河南開封"));
        studentList.add(new Student(4, "趙六", 18, "江西南昌"));

        //提取id
        List<Integer> idList = studentList.stream().map(Student::getId).collect(Collectors.toList());
        System.out.println(idList);

        //按照id分組
        Map<Integer, List<Student>> integerListMap = studentList.stream().collect(Collectors.groupingBy(Student::getId));
        System.out.println(integerListMap);

        //按照id爲key,name爲value 分組
        Map<Integer, String> integerStringMap = studentList.stream().collect(Collectors.toMap(Student::getId, Student::getName, (key1, key2) -> key2));
        System.out.println(integerStringMap);


    }
}

@NoArgsConstructor
@AllArgsConstructor
@Data
public class Student {

    private Integer id;

    private String name;

    private Integer age;

    private String address;


}