public class JexlEngineUtils {

   public static BigDecimal evaluateExpression (
         Map <String, Object> map, String[] elementArr, String expression, int margin
   ){

      JexlEngine jexl = new JexlEngine ();
      JexlContext jexlContext = new MapContext ();

      //需要set源代碼Math，否則報錯
 
      jexlContext.set("Math", Math.class);

      //需要set源代碼 BigDecimal，否則報錯

      jexlContext.set("BigDecimal",BigDecimal.class);

        for (String key : elementArr) {
         Object p = map.get ( key );
         Double val = 0.0;
         if (null != p) {
            if (p instanceof BigDecimal) {
               BigDecimal temp = (BigDecimal) p;
               val = temp.doubleValue ();
            } else {
               if (RegexUtils.isNumberWithDot ( p.toString () )) {
                  val = Double.valueOf ( p.toString () );
               }
            }
         }
         jexlContext.set ( key, val );
      }
      Expression e = jexl.createExpression ( expression );
      Object obj = e.evaluate ( jexlContext );
      BigDecimal result = new BigDecimal ( null == obj ? "0" : obj.toString () );
      return result.setScale ( margin, BigDecimal.ROUND_HALF_UP );
   }

   //因為精度問題引入BigDecimal

   public static void main(String[] args) {
      Map<String, Object> individualIncomeTaxMap = new HashMap<>(16);
      individualIncomeTaxMap.put("cashRate",5334.4);
      individualIncomeTaxMap.put("yearPremium",200000);
      String[] te = {"cashRate","yearPremium"};
      System.out.println(evaluateExpression(individualIncomeTaxMap,te,"Math.floor(BigDecimal.valueOf(cashRate).multiply(BigDecimal.valueOf(yearPremium).divide(BigDecimal.valueOf(1000))))",0));
   }
}

利用Jexl實現數據庫的計算公式在Java中執行