public class Source {
    private String sourceText;
    private NestedSource nestedSource;
    // Getters, Setters and toString()
}
public class NestedSource {
    private String nestedSourceText;
    // Getters, Setters and toString()
}
public class Destination {
    @JMap(value = "sourceText", classes = Source.class)
    private String destinationText;
    @JMap(value = "nestedSource", classes = Source.class)
    private NestedDestination nestedDestination;
    // Getters, Setters and toString()
}
public class NestedDestination {
    @JMap(value = "nestedSourceText", classes = NestedSource.class)
    private String nestedDestinationText = "Default Destination Text";
    // Getters, Setters and toString()
}
final Source source = new Source();
source.setSourceText("Source text");
source.setNestedSource(new NestedSource());
System.out.println(source);
final JMapper<Destination, Source> mapper = new JMapper<Destination, Source>(Destination.class, Source.class);
final Destination destination = mapper.getDestination(source, NullPointerControl.ALL, MappingType.ONLY_VALUED_FIELDS);
System.out.println(destination);

Source{sourceText='Source text', nestedSource=NestedSource{nestedSourceText='null'}}
Destination{destinationText='Source text', nestedDestination=NestedDestination{nestedDestinationText='null'}}

Source{sourceText='null', nestedSource=NestedSource{nestedSourceText='null'}}
Destination{destinationText='Default Destination Text', nestedDestination=NestedDestination{nestedDestinationText='null'}}