Java根据某一个字段分组

• 利用java 8新特性进行分组

 Map<Integer, List<SlhEvaluationAssignment>> collect = list.stream()
                    .collect(Collectors.groupingBy(SlhEvaluationAssignment::getTeamId));

• 然后循环得到对应的key和value

 for (Map.Entry<Integer, List<SlhEvaluationAssignment>> entry : collect.entrySet()) {
    Integer teamId = entry.getKey();
    List<SlhEvaluationAssignment> slhEvaluationAssignmentList = entry.getValue();
}

• 根据某个字段转为Map

Map<Integer, Apple> appleMap = appleList.stream().collect(Collectors.toMap(Apple::getId, a -> a,(k1,k2)->k1));