【求助】JAVA8 List<Map<>>中过滤出重复元素问题

Question

问题描述如下所示List数据结构：Listlist=newArrayList();Mapmap1=newHashMap();map1.put("order_no","123");map1.put("quantity",10);map1.put("amount",100);Mapmap2=newHashMap();map2.put("order_no","223");map2.put("quantity",15);map2.put("amount",150);Mapmap3=newHashMap();map3.put("order_no","123");map3.put("quantity",5);map3.put("amount",50);Mapmap4=newHashMap();map4.put("order_no","124");map4.put("quantity",6);map4.put("amount",60);Mapmap5=newHashMap();map5.put("order_no","223");map5.put("quantity",7);map5.put("amount",70);list.add(map1);list.add(map2);list.add(map3);list.add(map4);list.add(map5);有个需求是判断上述list中，是否存在有Map.key=order_no，其value重复，并将重复的项取出，如例子所示最后应该会抓到order_no=123,223,这两笔订单，我目前的写法是：//定义一个过渡用的list2与list一致Listlist2=newArrayList();list2.addAll(list);Listcollect=list.stream().filter(x->{longcount=list2.stream().filter(x2->x2.get("order_no").equals(x.get("order_no"))).count();if(count>1){//判断是否重复returntrue;}returnfalse;}).collect(Collectors.groupingBy(x->x.get("order_no"))).entrySet().stream().map(x->{Maptmp=newHashMap();tmp.put("key_order",x.getKey());tmp.put("order_list",x.getValue());returntmp;//分组展示重复的订单数据}).collect(Collectors.toList());目前虽然功能是实现的，但是考虑到订单量有数万笔乃至更多，重新定义了一个一样的过渡用list这样的写法比较粗糙，效能也不高，想请教下大家有没有更简洁高效优雅些的方式可以实现功能呢？

Answer 1

...你用set检查重复不就好了吗一遍循环就好了你这个太吓人
Setset=newHashSet<>();
Map>>valMap=newHashMap<>();
for(Mapitem:list){
Stringid=item.get("order_no").toString();
if(set.contains(id)){
List>l=valMap.computeIfAbsent(id,k->newArrayList<>());
l.add(item);
}
set.add(id);
}
for(Map.Entry>>entry:valMap.entrySet()){
System.out.println(JSON.toJSONString(entry.getValue()));
}
//print
//[{"order_no":"123","amount":50,"quantity":5}]
//[{"order_no":"223","amount":70,"quantity":7}]