如何轉換清單 <Object> 到地圖 <String , List<String> &gt;使用Java 8流？

Question

我有Employee對象，其中具有rowId，skillId和Student如下

[0, 20,"John"],

[1, 30,"Amy"],

[2, 20,"Tom"]

我需要這樣的回應：

Map<skillId, List<student>>

20 , ["John","Tom"]

30 , [Amy]

有人可以幫忙嗎？

Answer 1

嘗試使用groupingBy和mapping

list.stream()
     .collect(Collectors.groupingBy(Employee::getSkillId,
                    Collectors.mapping(Employee:getStudent, Collectors.toList())));

Answer 2

請使用以下內容，

Map<Integer, List<Employee>> collect = employeeList.stream()
                .collect(Collectors.groupingBy(Employee::getSkillId, Collectors.toList()));

Answer 3

Map<Integer, List<String>> skillAndList = list.stream().collect(Collectors.groupingBy(Employee::getSkillId, Collectors.mapping(Employee::getStudent, Collectors.toList())));
System.out.println(skillAndList);

輸出與您預期的相同-

{30=[Amy], 20=[John,Tom]}