List集合的stream流处理
1.List取出某个属性的集合 limit取前num条
List<T> list = list.stream().map(Bean::getField).limit(num)..List());
2.List转Map
Map<T,Bean> map =list.stream().Map(Bean::getField, Function.identity()));
Map<T,T> map =list.stream().Map(Bean::getField, Bean::getField()));
sortedlist3.List<Integer>转Llist<String>
list.stream().map(x -> x + "").List());
4.List根据某个属性分组
Map<Long, List<Long>> map3= list.stream().upingBy(Bean::getField,Collectors.mapping(Bean::List())));
5.List根据某个属性去重(两种写法均可)
list.stream().Collection(() -> new TreeSet<>(Comparatorparing(Bean::getField))), ArrayList::new));
list.stream().Map(x -> x.getSkuId(), x -> x, (x, y) -> x)).values().stream().List());
6.List将某个属性值累加
list.stream().map(Bean::getFiled).reduce(BigDecimal.ZERO, BigDecimal::add);
list.stream().collect(Collectors.summingLong(Bean::getFiled))；适⽤于Long、Int、Double
list.stream().Map(x-&SkuId(),x->x,(x, y)->{x.Field().Field()));return x;})).values().stream().List());
7.List过滤某个属性
List<T> list = list.stream().filter(x -> x.getField().equals("")...业务逻辑).map(y ->{..业务逻辑，可省略此部分}).List());
8.List<Map<String, String>>合并为Map<String,String>
Map<String, String> map = listMap.stream().filter(e -> !CollectionUtils.isEmpty(e)).reduce(map, (x, y) -> {x.putAll(y); return x;});
9.List分组
Lists.partition(list,num(代表分成num条数据为⼀组))
10.List根据某个属性排序
list.stream().sorted(Comparatorparing(Bean::getField)).List())；正序
list.stream().sorted(Comparatorparing(Bean::getField).reversed()).List())；倒序
list.stream().sorted(Comparatorparing(Bean::getField).thenComparing(Bean::getField)).List())；多个字段排序
11.List根据逗号分割为字符串不适⽤于中间有空字符的场景，分割后为：123,,567
<(",").join(list);
list.stream().map(Bean::getField).collect(Collectors.joining(","));
...待补充