Java8--小念頭

實際生產中遇到的問題

list -------轉化爲 Map<String,List<>>
BiPredicate----巧用，用於過濾不滿足的條件

 public void checkAmount(String mainId,List<PromItemAReq> promItemListReq,String status){ 
         // 規則設置的 限制數量
        List<TProductGroupBuyingSelectRuleDO> dbUserGrouplist = selectRuleDBTunnel.findModelByMainId(mainId); 
        dbUserGrouplist=dbUserGrouplist.stream().collect(Collectors.toList());
        Map<String, Integer>  dbugLimitMap = dbUserGrouplist.stream()
                .collect(toMap(TProductGroupBuyingSelectRuleDO::getUserGroupID,TProductGroupBuyingSelectRuleDO::getLimitCount));
        // Map <用戶選中的 用戶組- 商品list>
        Map<String, List<PromItemAReq>>  ugProductMap = promItemListReq.stream().collect(Collectors.groupingBy(PromItemAReq::getUserGroupID));
        // 如果limitcount = =傳入的count-------true
        BiPredicate<Integer,Integer> pricePred = (x,y) -> (ModelConvertorUtil.compareInt(x,y));
        for (String userGroupId : dbugLimitMap.keySet()) {
            // 如果傳入的用戶組的
            Check.check(isEmpty(ugProductMap.get(userGroupId)),"提交失敗，活動商品不滿足限制數量。");
            int limitCountDb = dbugLimitMap.get(userGroupId);
            int reqCount = ugProductMap.get(userGroupId).size();
            Check.check(!pricePred.test(limitCountDb,reqCount),"提交失敗，活動商品不滿足限制數量。");
        }
    }

怎麼去重

List<Student> list = Students.stream()
.collect(collectingAndThen(toCollection(() -> new TreeSet<>(comparingLong(Student::getId))), ArrayList::new));

List<ClassEntity> distinctClass = classEntities.stream().
collect(Collectors.collectingAndThen(Collectors.toCollection(() -> new TreeSet<>(Comparator.comparing(o -> o.getProfessionId() + ";" + o.getGrade()))),

 ArrayList::new));