JDK8的新特性--lambda表达式--分组管理

一. 测试对象

@Data
public class Grade {
    private String gradeName;   // 年级名称
    private String schoolName;  // 学校名称
    private Integer groupId;  // 学校年级属于某个分组
}

 

 

二. 测试方法

public List<Map<String, Object>> lambdaTest(){
        Grade gradeOne = new Grade();
        gradeOne.setGradeName("三年二班");
        gradeOne.setSchoolName("中国十中");
        gradeOne.setGroupId(1);
        Grade gradeTwo = new Grade();
        gradeTwo.setGradeName("二年级一班");
        gradeTwo.setSchoolName("中国十六中");
        gradeTwo.setGroupId(2);
        Grade gradeThree = new Grade();
        gradeThree.setGradeName("四年级三班");
        gradeThree.setSchoolName("中国一百零八中");
        gradeThree.setGroupId(1);
        Grade gradeFour = new Grade();
        gradeFour.setGradeName("六年级六班");
        gradeFour.setSchoolName("中国二十三中");
        gradeFour.setGroupId(2);

        List<Grade> gradeList = new ArrayList<>();
        gradeList.add(gradeOne);
        gradeList.add(gradeTwo);
        gradeList.add(gradeThree);
        gradeList.add(gradeFour);

        Map<Integer, List<Grade>> gradeMap = gradeList.stream().collect(Collectors.groupingBy(Grade::getGroupId));
        System.out.println(gradeMap.toString());

        List<Map<String, Object>> responseList = new ArrayList<>();
        gradeMap.forEach((key,value) -> {
            Map<String, Object> map = new HashMap<>();
            map.put("groupId", key);
            map.put("list", listConvertMap(value));
            responseList.add(map);
        });

        return responseList;
}

39 List<Map<String, Object>> listConvertMap(List<Grade> list){
        List<Map<String, Object>> responseList = new ArrayList<>();
        for (Grade grade : list) {
            Map<String, Object> map = new HashMap<>();
            map.put("schoolName", grade.getSchoolName());
            map.put("gradeName", grade.getGradeName());
            responseList.add(map);
        }
        return responseList;
}

 

 

三. 测试结果

 

四. 主要方法，lambda

/* 根据groupId进行一个区分 */
Map<Integer, List<Grade>> gradeMap = gradeList.stream().collect(Collectors.groupingBy(Grade::getGroupId));
// 结果 -> {1=[Grade(gradeName=三年二班, schoolName=中国十中, groupId=1), Grade(gradeName=四年级三班, schoolName=中国一百零八中, groupId=1)]
　　　　　　, 2=[Grade(gradeName=二年级一班, schoolName=中国十六中, groupId=2), Grade(gradeName=六年级六班, schoolName=中国二十三中, groupId=2)]}