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);

判断重复重：

if(partitionCamera.stream().anyMatch(item->
        item.getChannelNo().compareTo(deviceCamera.getChannelNo())==0 && item.getDeviceSerial().equals(deviceCamera.getDeviceSerial()))){
}

转map避免控指针

Map<String, String> map = xdsList.stream().collect(Collectors.toMap(XdsDtuEntity::getXMac, e->e.getXDtuDescribe()==null?"":e.getXDtuDescribe()));

将集合转为map  属性做键  对象做值
hutool 5.5.2版本
CollStreamUtil.toIdentityMap(hzOptionList, HzOption::getId)