I have a problem where I want to convert a list of POJOs into DTOs and pass them into a wrapper object which is then returned. Consider this working piece of code:
List<Device> devices = dbService.getDevices(...);
List<DeviceDTO> devicesDTO = new ArrayList<DeviceDTO>();
for (Device d : devices) {
devicesDTO.add(convertToDTO(d));
}
WrapperDTO wrapper = new WrapperDTO(devicesDTO);
I am looking for a way to rewrite this into smaller, maybe more elegant, piece of code using Java lambda expressions. This is what I have done so far. I can do the conversion from POJOs to DTOs but I am struggling to pass the list of DTOs to the constructor of a new wrapper object.
List<Device> devices = dbService.getDevices(...);
List<DeviceDTO> devicesDTO = devices.stream().map(d -> convertToDTO(d)).collect(Collectors.toList());
WrapperDTO wrapper = new WrapperDTO(devicesDTO);
How could I get it even shorter a one-liner, something like this?
WrapperDTO wrapper = devices.stream()........collect( () -> WrapperDTO:new);
Obviously, the last piece is not working but that is something I would like to achieve. Any suggestions? Thank you my friends:)
You may use collectingAndThen collector to solve it in one fell swoop. Use the toList collector as the downstream collector and pass the WrapperDTO::new constructor reference as the finisher function. Here's how it looks.
final WrapperDTO wrapper = devices.stream()
.map(d -> convertToDTO(d))
.collect(Collectors.collectingAndThen(Collectors.toList(), WrapperDTO::new));