java8 stream流的使用

List<Paper> list = new ArrayList<>();
list.add(new Paper("m",2L));
list.add(new Paper("a",1L));
list.add(new Paper("j",3L));
list.add(new Paper("t",4L));
list.add(new Paper("b",5L));

遍历：
list.stream().forEach(item ->{

});

排序：　List<Paper> collect = list.stream().sorted(Comparator.comparing(Paper::getPaperName)).collect(Collectors.toList());

分组：Map<String, List<Paper>> collect =list.stream().collect(Collectors.groupingBy(Paper::getPY))

最大最小值：

Optional<Paper> max =list.stream().max(Comparator.comparing(Paper::getPaperName));

if (max.isPresent()) {//防止空指针
......
}

转换map：
Map<Long, String> collect2 = list.stream().collect(Collectors.toMap(Paper::getPaperId, Paper::getPaperName));

过滤：
Optional<Paper> min = x.getSchedulingList().stream().filter(s -> s.id()>=1).min(Comparator.comparing(Paper::getPaperName));

价格类属性累加：
orderList.stream().map(OrderEntity::getRealFee).reduce(BigDecimal.ZERO, BigDecimal::add);