带数字键的MVEL表达式

Question

We are using MVEL to evaluate the expression by passing the map in the context object. The map contains SNMP trap information such as OID and its values. eg sample Map contains following Keys and values.

    Map<String,String> trapMap = new HashMap();
    trapMap.put("1.3.6.1.4.1.9.9.311.1.1.2.1.3", "(7362915) 20:27:09.15");
    trapMap.put("1.3.6.1.4.1.9.9.311.1.1.2.1.2", "2.2");
    trapMap.put("1.3.6.1.4.1.9.9.311.1.1.2.1.19", "0");
    trapMap.put("1.3.6.1.4.1.9.9.311.1.1.2.1.16", "SIMPLE TRAP --Port Down due to Admin Status down");
    trapMap.put("errorStatus", "0");
    trapMap.put("IPAddress", "10.127.34.219");

When we evaluate the expression using MVEL.eval() it either fails or return False. Following is the MVEL expression used and its result.

    System.out.println("----------########### = "+(MVEL.eval("1.3.6.1.4.1.9.9.311.1.1.2.1.19 == '0'", trapMap)));
    //Throws error as 
    //Exception in thread "main" [Error: invalid number literal: 1.3.6.1.4.1.9.9.311.1.1.2.1.19]
    //      [Near : {... 1.3.6.1.4.1.9.9.311.1.1.2.1.19 == '0 ....}]

    System.out.println("----------########### = "+(MVEL.eval("\"1.3.6.1.4.1.9.9.311.1.1.2.1.19\" == '0'", trapMap)));
    //Enclosed trap OID in double quotes and compared with String value then it returns false

    System.out.println("----------########### = "+(MVEL.eval("\"1.3.6.1.4.1.9.9.311.1.1.2.1.19\" == 0", trapMap)));
    //Enclosed trap OID in double quotes and compared with number then it returns false

Our Map will always contain such OID and values and we want to validate their values using MVEL. Based on this, we need to know

1. if the expression mentioned is a valid expression if not then what changes are required to make it work.
2. Do we need to add any additional escape characters to the keys mentioned in expression OR
3. This is not possible as the key mentioned in the expression is not valid property/identifier.

Answer 1

DOT(.) will create a problem in above expression. MVEL internally calls getter after each . property .

we can replace . with _ operator. Also need to add _ in the starting.

public static void main(String args[]) throws Exception {
        String s = "1.3.6.1.4.1.9.9.311.1.1.2.1.19 == 0";

        Map<String, String> trapMap = new HashMap();
        trapMap.put(convertDot("1.3.6.1.4.1.9.9.311.1.1.2.1.3"), "(7362915) 20:27:09.15");
        trapMap.put(convertDot("1.3.6.1.4.1.9.9.311.1.1.2.1.2"), "2.2");
        trapMap.put(convertDot("1.3.6.1.4.1.9.9.311.1.1.2.1.19"), "0");
        trapMap.put(convertDot("1.3.6.1.4.1.9.9.311.1.1.2.1.16"), "SIMPLE TRAP --Port Down due to Admin Status down");
        trapMap.put("errorStatus", "0");
        trapMap.put("IPAddress", "10.127.34.219");
        System.out.println(MVEL.eval(convertDot(s), trapMap));

    }

    public static String convertDot(String input) {
        input = "_" + input.replaceAll("\\.", "_");
        return input;
    }

output

true

Answer 2

If you are using Java Map, you can implicitly call the get method. The below code will evaluate the correct expression.

System.out.println("----------########### = "+(MVEL.eval("get(\"1.3.6.1.4.1.9.9.311.1.1.2.1.19\") == '0'", trapMap)));