Java prevent calling private or protected methods outside of class

Question

Let's supppose that I have created a Java library, called Foo and I have a class inside that library called Bar. Let's suppose further that in the Bar class I have a private method, called fooBar.

public class Bar {
    //...
    private Object fooBar() {
        //Do something
    }
    //...
}

One can run this method without any difficulties with a code written in a class, like this:

public static Object runMethod(Object object, String methodName) {
    Method method = object.getClass().getDeclaredMethod(methodName);
    method.setAccessible(true);
    return method.invoke(object);
}

However, let us suppose that we intend to discourage this habit for fooBar. How can we do something like that? Should we get the stack trace from somewhere and check where it was called? Or should we do something else?

Answer 1

You need a security manager...

https://docs.oracle.com/javase/tutorial/essential/environment/security.html

A security manager is an object that defines a security policy for an application. This policy specifies actions that are unsafe or sensitive. Any actions not allowed by the security policy cause a SecurityException to be thrown. An application can also query its security manager to discover which actions are allowed.

It supports disallowing setAccessible() to make private and protected methods invocable via reflection.