Question

I am working on a project, and am currently working on implementing some logging with log4j and I was curious about how I should go about implementing the logs. The two implementations I am kicking around are as follows:

First Option

Use single log from super class for that class and all sub classes:

public abstract class AbstractFoo {
    protected static Log LOG = LogFactory.getLog(AbstractFoo.class);

    ...
}

public class Foo extends AbstractFoo {
    public void someMethod() {
        LOG.info("Using abstract log");
    }
}

Second Option

Use individual logs for each class, super and subs:

public abstract class AbstractFoo {
    private static Log LOG = LogFactory.getLog(AbstractFoo.class);

    ...
}

public class Foo extends AbstractFoo {
    private static Log LOG = LogFactory.getLog(Foo.class);        

    public void someMethod() {
        LOG.info("Using own log");
    }
}

What makes more sense and why?

Answer 1

I wouldn’t do either. Instead I would make it use the correct class in both cases.

public abstract class AbstractFoo {
    protected final Log log = LogFactory.getLog(getClass());

    ...
}

public class Foo extends AbstractFoo {
    public void someMethod() {
        log.info("Using abstract log");
    }
}

If you are not doing lots of logging (which is a good idea anyway) you can use a method instead.

public abstract class AbstractFoo {
    protected Log log() { return LogFactory.getLog(getClass()); }

    ...
}

If there is a class which calls this a lot you can override it to give you a cached instance.