How to make a class configurable without adding any code?

Question

I would like to be able to write (in Java) something like the following:

public class A implements MagicallyConfigurable {

    @configuration_source_type{"xml"}
    @configuration_dir{"some/rel/path/"}

    /* or maybe some other annotations specifying a db-based configuration etc. */

    int length = 4 /* some kind of default */;
    char c = '*' /* some kind of default */;

    @do_not_configure
    String title;

    A(String title) {

        /* possibly, but hopefully no need to, something like:
        configure();
        call here. */

        this.title = title;
    }

    void goForIt() {
        System.out.println(title);
        for(int i=0; i < length; i++) {
            System.out.print(c);
        }
    }
}

and for it to work as expected. That is, the only thing I would need to initialize fields based on a configuration would be adding some annotations, implementing an interface and possibly making a single function call (but hopefully without it).

I'm sure this is theoretically doable, the question is whether there's an existing library/framework/add-on/thingie which enables it. (Maybe Apache commons.configuration somehow? Haven't worked with it before.)

Answer 1

What you can do, is to use Spring 3.0 EL. An example can be found here, but what it basically boils down to is that you can do the following:

@Value("#{systemProperties.databaseName}")
public void setDatabaseName(String dbName) { ... }

And your properties will be automatically set. This will work on setters and on properties.