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();
}