Java中找出List对象集合某个字段的重复值以及对该字段进行排重

1、 找出List对象集合某个字段的重复值

public static void main(String[] args) {
	List orderList = new ArrayList<>();
	for (int i=0;i<10;i++){
		OrderViewModel model = new OrderViewModel();
		model.setPcno("1111"+i);
		model.setProductQty(22+i);
		orderList.add(model);
	}
	OrderViewModel model1 = new OrderViewModel();
	model1.setPcno("11118");
	model1.setProductQty(955);
	orderList.add(model1);
	List list =orderList.stream().
			collect(Collectors.groupingBy(OrderViewModel::getPcno,Collectors.counting()))
			.entrySet().stream()
			.filter(entry->entry.getValue()>1)
			.map(Map.Entry::getKey)
			.collect(Collectors.toList());
	if(list.size()>0){
		System.out.println("groupingBy的字段有"+list.size()+"个重复，分别为：");
		list.forEach(System.out::println);
	}else{
		System.out.println("groupingBy的字段没有重复。");
	}
	List newOrder = removeDuplicateOrder(orderList);
	System.out.println(newOrder);
}

2、对List对象集合某个字段进行排重

private static List removeDuplicateOrder(List orderList) {
	Set set = new TreeSet<>(Comparator.comparing(OrderViewModel::getPcno));
	set.addAll(orderList);
	return new ArrayList<>(set);
}