BigDecimal 舍入模式（Rounding mode）介绍

[b]ROUND_CEILING[/b]
Rounding mode to round towards positive infinity.
向正无穷方向舍入

[b]ROUND_DOWN[/b]
Rounding mode to round towards zero.
向零方向舍入

[b]ROUND_FLOOR[/b]
Rounding mode to round towards negative infinity.
向负无穷方向舍入
[b]
ROUND_HALF_DOWN[/b]
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

[b]ROUND_HALF_EVEN[/b]
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


[b]ROUND_HALF_UP[/b]
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
[b]

ROUND_UNNECESSARY[/b]
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


[b]ROUND_UP[/b]
Rounding mode to round away from zero.
向远离0的方向舍入