jdk8 stream filter()的特殊用法及与map()比较

1.简单的filter和map的单独形式

List newlist = list.stream().map(Person::getName).collect(toList());

list = list.stream().filter(person -> person.getAge() == 20).collect(toList());

2.map与filter的位置互换

List cidList = userInfoEntities.stream().map(SisTspUserInfoEntity::getCid).filter(StringUtils::isNotBlank).distinct().collect(Collectors.toList());

 List cidList1 = userInfoEntities.stream().filter(x->x.getUserId() != 1).map(SisTspUserInfoEntity::getCid).distinct().collect(Collectors.toList());

3.distinct的一般过滤形式

 List phoneList5 = entities.stream().distinct().collect(Collectors.toList());

4.StreamEx过滤  合并多个stream

   List phoneList6 = StreamEx.of(entities).distinct(SisTspVehicleOwnerRecordEntity::getPhoneNumber).collect(Collectors.toList());

5.distinctByKey在使用filter时需要重定义

   List obj = refactorList.stream().filter(distinctByKey(basePlatFormReport::getVin)).collect(Collectors.toList());

    private static  Predicate distinctByKey(Function keyExtractor) {
        Map seen = new ConcurrentHashMap<>();
        return t -> seen.putIfAbsent(keyExtractor.apply(t), Boolean.TRUE) == null;
    }