java_lambda.md

Conver list in list to single list

List<String> keyList = machineDataPayload.getMessages()
          .stream()
          .map(messages ->
                  messages.getParameters()
                          .stream()
                          .map(Parameter::getKey)
                          .collect(Collectors.toList()))
          .flatMap(Collection::stream)
          .collect(Collectors.toList());