Mvel动态表达式

Question

你知道是否可以用Mvel动态计算一个表达式。例如：

VariableResolverFactory functionFactory = new MapVariableResolverFactory();
MVEL.eval("def SUM(op1,op2,op3) { result=0B; if(op1) result+=op2; else result+=op3; }  return result; ",functionFactory);

ParserContext ctx = new ParserContext()
Serializable s = MVEL.compileExpression("SUM(op1,op2,op3)", ctx);
contextMapFct.put("op1", "5 > 3"); // just as an example if it's useless
contextMapFct.put("op2", new BigDecimal(10));
contextMapFct.put("op3", new BigDecimal(30));
Object obj= MVEL.executeExpression(s, contextMapFct, this.functionFactory);

Answer 1

做了很少的改变

1.)Brace在最后一次添加，是在return result;之前关闭。

(2) int result=0，添加了声明。

3. if(op1 == 'true')，它不是以boolean的形式出现，而是以String的形式出现

VariableResolverFactory functionFactory = new MapVariableResolverFactory();
MVEL.eval(
        "def SUM(op1,op2,op3) { int result=0; if(op1 == 'true') result+=op2; else result+=op3;   return result; }",
        functionFactory);

ParserContext ctx = new ParserContext();
Serializable s = MVEL.compileExpression("SUM(op1,op2,op3)", ctx);
Map contextMapFct = new HashMap();
contextMapFct.put("op1", "5 > 3"); // just as an example if it's useless
contextMapFct.put("op2", new BigDecimal(10));
contextMapFct.put("op3", new BigDecimal(30));
Object obj = MVEL.executeExpression(s, contextMapFct, functionFactory);
System.out.println(obj);

输出

30