How to call Java method that stored in string variable

Question

first, this is not similar to other questions because expressions contains parameters.

assume we have this method:

 public static int test(int x, Double y) {
    return somthing
}

and we have string expression like this:

 String expression = "test(1, 2)";

so how can we run this expression ?

I want to write a method with parameter and call it from a expression .

I can't find any library to solve this problem.

please help

Do you know what input you are going to have? For example if you are creating a calculator you can enter some expressions like: sum, divide, minus which are limited number and you know them all. Or your use case should cover any kind of method name given in the expression? — Aethernite, May 20 '21 at 13:40
Your basically talking about writing a parser here. https://stackoverflow.com/questions/34432136/writing-parser-of-a-simple-language — markspace, May 20 '21 at 13:42
@Aethernite I know that. I edit the question. I want to write a method with parameter and call it as a expression — meis, May 20 '21 at 13:45
@markspace thanks. I think you right. can you give a good example? — meis, May 20 '21 at 13:49
for simple things like this, you can even get it by using simple String operations, what have you tried so far? — Stultuske, May 20 '21 at 13:49
Check this thread -> https://stackoverflow.com/questions/160970/how-do-i-invoke-a-java-method-when-given-the-method-name-as-a-string You can use reflection the get the method using its name but for the parameters you have to parse the string to get them. For example you can use a regex to extract them and then parse them into the wanted format. — Aethernite, May 20 '21 at 13:51
@Stultuske assume this expression ` "func_round(func_areaUnderCurve(x) * y + 10000)"` — meis, May 20 '21 at 13:52

score 2 · Accepted Answer · answered May 20 '21 at 13:55

You can use the Script Engine with a scripting language, such as JavaScript, to handle your expressions.

package expression;

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

public class App 
{
    public static void main( String[] args )
    {
        ScriptEngineManager manager = new ScriptEngineManager();
        ScriptEngine engine = manager.getEngineByName("nashorn");
        try {
            engine.eval("var test = Packages.expression.App.test");
            Object result = engine.eval("test(1,2)");
            System.out.println(result);
        } catch (ScriptException e) {
            //TODO: handle exception
            e.printStackTrace();
        }
    }

    public static int test(int x, Double y) {
        return x;
    }
}

The line "var test = Packages.expression.App.test" creates an alias to your method.

The line Object result = engine.eval("test(1,2)"); calls your method.

You need to include the following dependency to your maven pom.xml:

<dependency>
  <groupId>org.openjdk.nashorn</groupId>
  <artifactId>nashorn-core</artifactId>
  <version>15.1</version>
</dependency>

How to call Java method that stored in string variable

1 Answers1