如何使用收集器,以转化的DAO的列表,到 Map<String, List<Pojo>>
daoList看起来是这样的:
[0] : id = "34234", team = "gools", name = "bob", type = "old"
[1] : id = "23423", team = "fool" , name = "sam", type = "new"
[2] : id = "34342", team = "gools" , name = "dan", type = "new"
我想GROUPBY“团队”属性,并为每个团队名单,具体如下:
"gools":
["id": 34234, "name": "bob", "type": "old"],
["id": 34342, "name": "dan", "type": "new"]
"fool":
["id": 23423, "name": "sam", "type": "new"]
POJO看起来是这样的:
@Data
@NoArgsConstructor
@AllArgsConstructor(access = AccessLevel.PUBLIC)
public class Pojo{
private String id;
private String name;
private String type;
}
这是我正在努力做到这一点,显然是错误的方法:
public Team groupedByTeams(List<? extends GenericDAO> daoList)
{
Map<String, List<Pojo>> teamMap= daoList.stream()
.collect(Collectors.groupingBy(GenericDAO::getTeam))
}
您当前的集电极- .collect(Collectors.groupingBy(GenericDAO::getTeam))
-正在生成Map<String,List<? extends GenericDAO>>
。
为了产生一个Map<String, List<Pojo>>
,你有你的转换GenericDAO
的实例为Pojo
通过链接一个实例Collectors.mapping()
收集到Collectors.groupingBy()
集电极:
Map<String, List<Pojo>> teamMap =
daoList.stream()
.collect(Collectors.groupingBy(GenericDAO::getTeam,
Collectors.mapping (dao -> new Pojo(...),
Collectors.toList())));
这是假设你有一些Pojo
接收一个构造函数GenericDAO
实例或相关GenericDAO
性。
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