Stream用法
GroupBy
Map<String, Set<String>> sourceTargetsMap = staticEdges.stream()
.collect(Collectors.groupingBy(EdgeModel::getSource, Collectors.mapping(EdgeModel::getTarget, Collectors.toSet())));
Map<String, Set<String>> sourceTargetsMap = staticEdges.stream()
.collect(Collectors.groupingBy(EdgeModel::getSource, Collectors.mapping(EdgeModel::getTarget, Collectors.toSet())));