If you don't mind a third party dependency, there is a class named Collectors2 in Eclipse Collections which contains methods returning Collectors for summing and summarizing BigDecimal and BigInteger. These methods take a Function as a parameter so you can extract a BigDecimal or BigInteger value from an object.
List<BigDecimal> list = mList(
BigDecimal.valueOf(0.1),
BigDecimal.valueOf(1.1),
BigDecimal.valueOf(2.1),
BigDecimal.valueOf(0.1));
BigDecimal sum =
list.stream().collect(Collectors2.summingBigDecimal(e -> e));
Assert.assertEquals(BigDecimal.valueOf(3.4), sum);
BigDecimalSummaryStatistics statistics =
list.stream().collect(Collectors2.summarizingBigDecimal(e -> e));
Assert.assertEquals(BigDecimal.valueOf(3.4), statistics.getSum());
Assert.assertEquals(BigDecimal.valueOf(0.1), statistics.getMin());
Assert.assertEquals(BigDecimal.valueOf(2.1), statistics.getMax());
Assert.assertEquals(BigDecimal.valueOf(0.85), statistics.getAverage());
Note: I am a committer for Eclipse Collections.