java 对List集合中元素对象按字段分组,并收集指定字段的值

一、实现:对已有对象集合List ,需要获取Persion对象的字段 name分组, 并对年龄age字段值做收集

二、字段分组收集方法

 注:由于实际业务只有String类型跟数字类型,所以只对String跟Object两种类型判空

        public static  Map> groupAndCollectionField(List list, Function groupFunction, Function getFiledFunction) {        if (Objects.isNull(list)) {            return new HashMap<>();        }        //按寄收类型分组, 并收集区号(机场)        Map> setMap = list.stream().filter(r-> {                    K groupValue = groupFunction.apply(r);                    V filedValue = getFiledFunction.apply(r);                    //分组判空                    boolean groupNull = Objects.isNull(groupValue);                    if (!groupNull && groupValue instanceof String) {                        groupNull = ((String) groupValue).length() == 0;                    }                    //字段判空                    boolean filedNull = Objects.isNull(filedValue);                    if (filedValue instanceof String) {                        filedNull = ((String) filedValue).length() == 0;                    }                    //分组非空 and 字段非空 返回true; 否则返回false                    return !groupNull && !filedNull;                })                .collect(Collectors.groupingBy(groupFunction, Collectors.mapping(getFiledFunction, Collectors.toSet())));        return setMap;    }

三、测试代码

        //场景1        System.out.println("场景1");        List persionList = new ArrayList<>();        persionList.add(new Persion(1, "李二", null));        persionList.add(new Persion(2, null, 30));        persionList.add(new Persion(3, "王五", 15));        persionList.add(new Persion(4, "陈十一", 11));        //分组并收集字段        Map> setMap = Main.groupAndCollectionField(persionList, Persion::getName, Persion::getAge);        //遍历        setMap.entrySet().stream().forEach(r-> System.out.println(String.format("name:%s; age:%s",r.getKey(),r.getValue())));        System.out.println("");                //场景2        System.out.println("场景2");        persionList = new ArrayList<>();        persionList.add(new Persion(1, "李二", 22));        persionList.add(new Persion(2, "李二", 30));        persionList.add(new Persion(3, "王五", 15));        persionList.add(new Persion(4, "陈十一", 11));        //分组并收集字段        setMap = Main.groupAndCollectionField(persionList, Persion::getName, Persion::getAge);        //遍历        setMap.entrySet().stream().forEach(r-> System.out.println(String.format("name:%s; age:%s",r.getKey(),r.getValue())));    }

四、结果

来源地址：https://blog.csdn.net/tingyesiyu/article/details/130803702