http://download.oracle.com/technetwork/java/javase/6/docs/zh/api/java/math/class-use/BigDecimal.html
http://jingyan.baidu.com/article/6d704a130a500f28db51ca09.html
http://jeelee.iteye.com/blog/652003/
金融工具类
原文：http://my.oschina.net/httpssl/blog/468734
