How to access the value of a private attribute in a Java class without a public method?

Question

How can I access the value of a private attribute in a class, a class in another package, without using an access method, such as a getter?

class Person{
   private String name = "Someone";
}

Why would anyone do that?

One of the reasons is that you may need to serialize objects such as the Jackson makes, transforming the values of class fields into JSON. I can access using field getters, but in case I don’t have them, or they don’t follow the Javabeans pattern, in the example getName, how I access the value of the field directly. Jackson itself allows you to set up if you want to access through setters and getters, or with the fields directly. There is a real performance gain.

Answer 1

You can use Reflection:

import java.lang.reflect.Field;

public class Expose {

    public static void main(String[] args) {
        Person person = new Person();
        Field secretField = null;
        try {
            secretField = Person.class.getDeclaredField("name");
        }
        catch (NoSuchFieldException e) {
            System.err.println(e);
            System.exit(1);
        }
        secretField.setAccessible(true); // break the lock!
        try {
            String wasHidden = (String) secretField.get(person);
            System.out.println("person.name = " + wasHidden);
        }
        catch (IllegalAccessException e) { 
            // this will not happen after setAcessible(true)
            System.err.println(e);
        }   
    }
}

Adapted example of https://github.com/fluentpython/example-code/blob/master/09-pythonic-obj/private/Expose.java