java 8 lambda 표현 식 집합 처리

선별 시리즈

//          
List pList = classImagePraiseService.list(lambdaQueryWrapperTow);
//           name    
List name= list.stream().map(p -> p.getName()).collect(Collectors.toList());
//           name            Id   333
List teacherIds = pList.stream().filter(s -> s.getId().equals("333")).map(p -> p.getUserId()).collect(Collectors.toList());
//     sort        (  )
pList .sort(Comparator.comparing(ClassImagePraise::getSort));
//     sort         (  )
pList .sort(Comparator.comparing(ClassImagePraise::getSort).reversed());

정렬 시리즈 상세

	List list = getMessageList();
    if (list != null && !list.isEmpty()){
        System.out.println("===     ===");
        list.stream().forEach(item -> System.out.println(item));

        //         ,   msg(  ),   id(  )
        list.sort(Comparator.comparing(Message:: getMsg).thenComparing(Message::getId));

        //         ,   msg(  ),   id(  )
        list.sort(Comparator.comparing(Message:: getMsg).thenComparing(Comparator.comparing(Message::getId).reversed()));

        //         ,   msg(  ),   id(  )
        list.sort(Comparator.comparing(Message:: getMsg).thenComparing(Message::getId).reversed());

        //         ,   msg(  ),   id(  )
        list.sort(Comparator.comparing(Message:: getMsg).reversed().thenComparing(Message::getId));

        System.out.println("===     ===");
        list.stream().forEach(item -> System.out.println(item));

List 구 화, 최대 치, 평균 값 구하 기

private static void statisticsList(){
        List list = getMessageList();
        //  
        Long sum= list.stream().mapToLong(Message::getId).sum();
        System.out.println("sum = " + sum);

        //    
        Optional maxMassage = list.stream().collect(Collectors.maxBy(Comparator.comparing(Message::getId)));
        Long maxId = maxMassage.get().getId();
        System.out.println("maxId = " + maxId);


        LongSummaryStatistics lss = list.stream().collect(Collectors.summarizingLong(Message::getId));
        System.out.println("sum = " + lss.getSum());
        System.out.println("max = " + lss.getMax());
        System.out.println("min = " + lss.getMin());
        System.out.println("avg = " + lss.getAverage());
}