There are cases where a fine-grained control of the string representation of logged objects in log messages would be useful.

When logging Class objects for instance, we would like to see the fully-qualified name of the given class in the log message. Currently we get (class|interface) com.acme.Foo, though, as per the implementation of j.l.Class#toString(), which prepends the type of the given class object.

As workaround, we currently define the log method to accept a String parameter and pass myClass.getName() to it. Having a strongly typed log method which takes the "real" object as parameter seems preferable, though.

A possible solution could be a mechanism which allows to register to-string converters for given types with a logger:

//Provided by JBoss Logging API
public interface StringConverter<T> {
    String createString(T object);
}

//A project-specific implementation
public class ClassStringConverter implements StringConverter<Class<?>> {
    public String createString(Class<?> object) {
        return object.getName();
    }
}

//Project-specific logger, references 1..n converters
@MessageLogger(projectCode = "HV", converters=ClassStringConverter.class)
public interface Log extends BasicLogger {

    //implementation uses converter to create string representation of given class
    @LogMessage(level = INFO)
    @Message(id = 1, value = "Illegal class %s")
    void illegalClass(Class<?> clazz);
}

Would such a feature make sense to you?