@Converter(autoApply = true)
public class AttributeListConverter implements AttributeConverter<List<Attribute>, String> {
 ...
}

@Converter(autoApply = true)
public class StringListConverter implements AttributeConverter<List<String>, String> {
 ...
}

@Entity
public class Sample {
 ...

private List<String> list = new ArrayList<String>(0);
 ...
}