How to write into a private fiald from the outer world?

Question

Hello,
I have just got some strange rerults and want to share them with you.
I'm writing a bean class. Each field of the bean conforms to a column in a table of the database. The bean is filled with a record of database from database by Entity Factory and is returned to me. I have not seen the sources of the Entity Factory system. The beans are entities that have setter and getters.
All my colegues use a standard scheme with private field (named as a column in the database) and setter/getter for it. I have deriviated from this scheme creating a virtual property; that is only setter and getter with no private field. And the Entity Factory started crushing! It cannot find the private field anymore to write data from a table into it!
I had an experiment adding the private field with the final modifier. And what do you think I've got in effect? The entity Factory started complaining that it CANNOT SET A PRIVATE FIELD BECAUSE IT IS MARKED WITH FINAL! Removing the final has solved the problem.
Can you beleive this story? As the system is Enterprise, I would think that application server would sublass my implementation. But the privates should be inaccessible anyway. I'm going to look into source codes tomorrow.

Answer 1

As Kayaman says, you can get around the restriction described in the JLS by use of Reflection.
Consider the following example:
class SimpleKeyPair {
    private String privateKey = "original"; // private field
public class ReflectionChecker {
    public static void main(String[] args) throws Exception {
        SimpleKeyPair keyPair = new SimpleKeyPair();
        Class c = keyPair.getClass();
        // get the reflected object
        Field field = c.getDeclaredField("privateKey");
        // set accessible true
        field.setAccessible(true);
        System.out.println("Value of privateKey: " + field.get(keyPair)); // prints "original"
        // modify the member varaible
        field.set(keyPair, "altered");
        System.out.println("Value of privateKey: " + field.get(keyPair)); // prints "altered"
}