BigDecimal除法运算报错，错误如下：
Non-terminating decimal expansion; no exact representable decimal result
原因是：
BigDecimal divide(BigDecimal divisor, int scale, int roundingMode)
if divisor is zero, roundingMode==ROUND_UNNECESSARY and the specified scale is insufficient to represent the result of the division exactly
所以应该指定scale和roundingMode，保证对于无限小数有足够的范围来表示结果。