Jackson serialize only interface methods
You have two options:
1) put @JsonSerialize
annotation on your interface (see @broc.seib answer)
2) or use specific writer for the serialization (as of Jackson 2.9.6):
ObjectMapper mapper = new ObjectMapper();
String str = mapper.writerFor(Interf.class).writeValueAsString(interf);
Just annotate your interface such that Jackson constructs data fields according to the interface's class and not the underlying object's class.
@JsonSerialize(as=Interf.class)
public interface Interf {
public boolean isNo();
public int getCountI();
public long getLonGuis();
}