英文:
converting foreach to filter
问题
我想将代码从这样：
List<FlightPositionRoute> flightPositionRoutes = new ArrayList<>();
dtos.stream()
.map(a -> positions.getPositions(a.getId().getValue()))
.forEach(flightPositionRoute -> flightPositionRoute.ifPresent(flightPositionRoutes::add));
转换为这样：
List<FlightPositionRoute> flightPositionRoutes = dtos.stream()
.map(a -> positions.getPositions(a.getId().getValue()))
.filter(Optional::isPresent)
.map(Optional::get)
.collect(Collectors.toList());
我的意思是，我想使用 filter 代替 foreach，因为它更优雅 
不过，很遗憾，我遇到了这个问题：
Required type: List<FlightPositionRoute>
Provided: List<Optional<FlightPositionRoute>>
如何修复这个问题？
英文:
I would like to convert
List<FlightPositionRoute> flightPositionRoutes = new ArrayList<>();
dtos.stream()
.map(a-> positions.getPositions(a.getId()
.getValue()))
.forEach(flightPositionRoute ->
flightPositionRoute.ifPresent(flightPositionRoutes::add));
To this:
List<FlightPositionRoute> flightPositionRoutes = dtos.stream()
.map(a-> positions.getPositions(a.getId()
.getValue()))
.filter(Optional::isPresent)
.collect(Collectors.toList());
I mean I would like to use filter instead of foreach, because it's prettier
Unfortunately, I'm getting
Required type: List <FlightPositionRoute>
Provided: List <Optional<FlightPositionRoute>>
How can I repair it?
答案1
得分: 2
你只需要解开 Optional：
List<FlightPositionRoute> flightPositionRoutes = dtos.stream()
.map(a -> positions.getPositions(a.getId().getValue()))
.filter(Optional::isPresent)
.map(Optional::get)
.collect(Collectors.toList());
英文:
You just need to unpack the Optional:
List<FlightPositionRoute> flightPositionRoutes = dtos.stream()
.map(a-> positions.getPositions(a.getId().getValue()))
.filter(Optional::isPresent)
.map(Optional::get)
.collect(Collectors.toList());
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