How do I get a variable value from a String in Java?

Question

So I am writing a debugger plugin for Minecraft bukkit and I was wondering how to get a public static variable value from a String. Here is some example code:

package example.package;

public class Ex {
 public static String foo = "bar";
}

If I were to give it the string "example.package.Ex.foo" it should return "bar", how do I do this?

Answer 1

using java 11(Reflection API) - you can do this in older java versions too

public class Main {
    public static void main(String[] args) {
        var _this = new Main();
        _this.doJob();
    }
    
    void doJob() {
        var classLoader = this.getClass().getClassLoader();
        try {
            var loaded = classLoader.loadClass("example.package.Ex");
            var obj = new Object();
            var field = loaded.getField("foo");
            System.out.println(field.get(obj));
        } catch (ClassNotFoundException | NoSuchFieldException | IllegalAccessException e) {
            e.printStackTrace();
        }
    }
}

Edit A generic approach would be like this:

<T> T getFieldValueAtRuntime(String field) throws ClassNotFoundException, NoSuchFieldException, IllegalAccessException {
    var classLoader = this.getClass().getClassLoader();
    final var endIndex = field.lastIndexOf('.');
    final var fullClassName = field.substring(0, endIndex);
    final var fieldName = field.substring(endIndex + 1);
    var loadedClass = classLoader.loadClass(fullClassName);
    var obj = new Object();
    var fieldOfLoadedClass = loadedClass.getField(fieldName);
    return (T) fieldOfLoadedClass.get(obj);
}
-------------------------
try {
    String fieldValue = _this.getFieldValueAtRuntime("example.package.Ex.foo");
    System.out.println(fieldValue);
} catch (ClassNotFoundException | NoSuchFieldException | IllegalAccessException e) {
    e.printStackTrace();
}