Java8 : Map list of objects by key

Question

Map<A, List<B>> xFunction() {    
    Map<A, List<B>> mapList = new HashMap<>();
    List<A> aList = x.getAList();
    for (A a : aList) {
        List<B> bList = getBList(a.getId());
        mapList.put(a, bList);
    }
    return mapList;
}

如何在 java 8 中使用收集和分组或映射来转换它？

我尝试使用类似的东西:

x.getAList
.stream()
.map(a -> getBList(a.getId)) //return a list of B
.collect(Collectors.groupingBy (...) )

干杯

Answer 1

您需要Collectors.toMap:

Map<A, List<B>> map =
    x.getAList()
     .stream()
     .collect(Collectors.toMap (Function.identity(), a -> getBList(a.getId())));