数学公式解析和计算

JEP
http://www.singularsys.com/jep/
https://sourceforge.net/projects/jep/
http://rabbit8.bokee.com/3936531.html
http://suneca.com/article.asp?id=28

http://www.javaeye.com/topic/58422里办法多

关于jexl
1,jexl1.1计算分母为0的表达式时，竟然算出来的值为0，被某人说没有逻辑https://issues.apache.org/jira/browse/JEXL-45
2,jexl2解决了这个问题，但jexl2依赖jdk5
https://issues.apache.org/jira/browse/JEXL-58
handles ArithmeticException (divide by zero)
division by zero ignored only if JexlEngine.isSilent()

JexlEngine jexl  =   new  JexlEngine();
jexl.setCache( 512 ); // 有何用
jexl.setLenient( false ); // 什么意思
jexl.setSilent( false );

String calculate  =   " (G1 + G2)/2 " ;
Expression e  = jexl.createExpression(calculate);
//  populate the context
JexlContext context  =   new  MapContext();
context.set( " G1 " ,  " 3 " );
context.set( " G2 " ,  " 5 " );
Object res  =  e.evaluate(context); //silent 为false时evaluate方法会抛异常，为true不抛异常但res为null

           
另外，利用oracle计算,如果分母为0会报ORA-01476: divisor is equal to zero