BigDecimal 舍入模式（Rounding mode）介绍

*ROUND_CEILING*
Rounding mode to round towards positive infinity.
向正无穷方向舍入

*ROUND_DOWN*
Rounding mode to round towards zero.
向零方向舍入

*ROUND_FLOOR*
Rounding mode to round towards negative infinity.
向负无穷方向舍入

*ROUND_HALF_DOWN*
Rounding mode to round towards "nearest neighbor" unless both neighbors are equidistant, in which case round down.
向（距离）最近的一边舍入，除非两边（的距离）是相等,如果是这样，向下舍入, 例如1.55 保留一位小数结果为1.5

*ROUND_HALF_EVEN*
Rounding mode to round towards the "nearest neighbor" unless both neighbors are equidistant, in which case, round towards the even neighbor.
向（距离）最近的一边舍入，除非两边（的距离）是相等,如果是这样，如果保留位数是奇数，使用ROUND_HALF_UP ，如果是偶数，使用*ROUND_HALF_DOWN*

*ROUND_HALF_UP*
Rounding mode to round towards "nearest neighbor" unless both neighbors are equidistant, in which case round up.
向（距离）最近的一边舍入，除非两边（的距离）是相等,如果是这样，向上舍入, 1.55保留一位小数结果为1.6

*ROUND_UNNECESSARY*
Rounding mode to assert that the requested operation has an exact result, hence no rounding is necessary.
计算结果是精确的，不需要舍入模式

*ROUND_UP*
Rounding mode to round away from zero.
向远离0的方向舍入

BigDecimal a = new BigDecimal("1.123141241");
BigDecimal b = new BigDecimal("0.1243521");
BigDecimal c = a.divide(b,new TextContent(20,RoundingMode.ROUND_HALF_UP));
//TextContent表示两者相除后结果的数学环境，第一个参数用来表示结果的小数位数，第二个参数即用来指定相应的舍入模式