Evaluate String as a condition Java

Question

I have to retrieve a set of column values from D/B and check it as a condition.

For example, I will have strings like "value > 2", "4 < value < 6" in a D/B column. (value is the one which is compared all the time). I will have a variable value declared in my code and I should evaluate this condition.

int value = getValue();
if (value > 2)  //(the string retrieved from the D/B)
  doSomething();

How can I do this?? Any help is muceh appreciated. Thanks.

Answer 1

Here is an example using the standard (Java 1.6+) scripting library:

import javax.script.ScriptEngine;
import javax.script.ScriptEngineManager;

public class Test {

    public static void main(String[] args) throws Exception {
        ScriptEngineManager factory = new ScriptEngineManager();
        ScriptEngine engine = factory.getEngineByName("JavaScript");

        engine.eval("value = 10");
        Boolean greaterThan5 = (Boolean) engine.eval("value > 5");
        Boolean lessThan5 = (Boolean) engine.eval("value < 5");

        System.out.println("10 > 5? " + greaterThan5); // true
        System.out.println("10 < 5? " + lessThan5); // false
    }
}