// .fetch("details.product","id")
.order().asc("id").findList();
Order order = orders.get(0);
JsonWriteOptions options = JsonWriteOptions.parsePath("*,details(id,orderQty,product(id))");
String jsonOrder = jsonContext.toJson(order, options);
System.out.println(jsonOrder);
Order o2 = jsonContext.toBean(Order.class, jsonOrder);