Java Stream - 如何将BigDecimal映射为双精度并计算平均值

import java.math.BigDecimal;
import java.util.stream.Stream;

public class Main {

  public static void main(String[] args) throws Exception {

    Stream.of(new BigDecimal("1.2"), new BigDecimal("3.7"))
        .mapToDouble(BigDecimal::doubleValue).average()
        .ifPresent(System.out::println);
  }
}