CalculatorHandler.java

@Component
public class CalculatorHandler {
  public Mono<ServerResponse> add(final ServerRequest request) {
    return calculate(request, (v1, v2) -> v1 + v2);
  }
  public Mono<ServerResponse> subtract(final ServerRequest request) {
    return calculate(request, (v1, v2) -> v1 - v2);
  }
  public Mono<ServerResponse> multiply(final ServerRequest request) {
    return calculate(request, (v1, v2) -> v1 * v2);
  }
  public Mono<ServerResponse> divide(final ServerRequest request) {
    return calculate(request, (v1, v2) -> v1 / v2);
  }
  private Mono<ServerResponse> calculate(final ServerRequest request,
      final BiFunction<Integer, Integer, Integer> calculateFunc) {
    final Tuple2<Integer, Integer> operands = extractOperands(request);
    return ServerResponse
        .ok()
        .body(Mono.just(calculateFunc.apply(operands.getT1(), operands.getT2())), Integer.class);
  }
  private Tuple2<Integer, Integer> extractOperands(final ServerRequest request) {
    return Tuples.of(parseOperand(request, "v1"), parseOperand(request, "v2"));
  }
  private int parseOperand(final ServerRequest request, final String param) {
    try {
      return Integer.parseInt(request.queryParam(param).orElse("0"));
    } catch (final NumberFormatException e) {
      return 0;
    }
  }
}