Java------Stream流式编程高级API【groupingBy、flatMap】(六)
Java------Stream流式编程高级API【groupingBy、flatMap】(六)
groupingBy 分组分类
groupingBy分组分类,可以通过单个属性字段进行分组分类,
此时的key就是单个属性字段。
比如:
list.stream().
collect(Collectors.groupingBy(x -> x.getAreaId()));
案例:
List list = new ArrayList<>();
for (int i = 0; i < 10; i++) {
PmAreasT pmAreasT = new PmAreasT();
pmAreasT.setAreaId(“i”+i);
list.add(pmAreasT);
}
for (int i = 0; i < 10; i++) {
PmAreasT pmAreasT = new PmAreasT();
pmAreasT.setAreaId(“i”+i);
list.add(pmAreasT);
}
Map<String, List> collect = list.stream().
collect(Collectors.groupingBy(x -> x.getAreaId()));
Set<Map.Entry<String, List>> entries2 = collect.entrySet();
for (Map.Entry<String, List> entry : entries2) {
entry.getValue().forEach(x->x.setAreaDesc(“asd”));
}
groupingBy分组分类,可以通过多个属性字段联合属性进行分组分类
比如:
list.stream().
collect(Collectors.groupingBy(x -> x.getAreaId()+x.getAreaCode()+x.getItmId()));
此时的key是多个属性字段拼接而成。案例:
List list = new ArrayList<>();
for (int i = 0; i < 10; i++) {
PmAreasT pmAreasT = new PmAreasT();
pmAreasT.setAreaId(“i”+i);
list.add(pmAreasT);
}
for (int i = 0; i < 10; i++) {
PmAreasT pmAreasT = new PmAreasT();
pmAreasT.setAreaId(“i”+i);
list.add(pmAreasT);
}
Map<String, List> collect = list.stream().
collect(Collectors.groupingBy(x -> x.getAreaId()+x.getAreaCode()+x.getItmId()));
Set<Map.Entry<String, List>> entries2 = collect.entrySet();
for (Map.Entry<String, List> entry : entries2) {
entry.getValue().forEach(x->x.setAreaDesc(“asd”));
}