ObjectWriter ow = new ObjectMapper().writer().withDefaultPrettyPrinter();
System.out.println("Map of Object[0]: " + ow.writeValueAsString(v.getAccessor().getObject(0)));
System.out.println("Map of Object[1]: " + ow.writeValueAsString(v.getAccessor().getObject(1)));
ByteArrayOutputStream stream = new ByteArrayOutputStream();
JsonWriter jsonWriter = new JsonWriter(stream, true);
FieldReader reader = v.get("col", MapVector.class).getAccessor().getReader();