Deserializing JSON into typed class - json

Question

I have a base class and two sublcasses:
public /*abstract*/ class TargetPoi {
private String poiId;
...
}
public class TargetSub1Poi extends TargetPoi {
private String oneMoreId;
...
}
public class TargetSub2Poi extends TargetPoi {
...
}
Is it possible to declare the base class abstract? ...I always get an exception when a JSON is send with the request if I use the abstract keyword...
Exception Description: This class does not define a public default constructor, or the constructor raised an exception.
Internal Exception: java.lang.InstantiationException
Descriptor: XMLDescriptor(com.foo.bar.TargetPoi --> [])
When the POST request with its JSON in the request body is coming into the Jersy Resource I want to deserialize the JSON into the proper TargetPoi subclasses.
The JSON:
{
"requestId": "84137f1ab38f4bf585d13984fc07c621",
"startTime": "2013-10-30T18:30:00+02:00",
"endTime": "2013-10-30T18:45:00+02:00",
"targetPoi":
{
"poiId": "0000000602",
"oneMoreId": "1"
},
"type": "Block",
"notification": true
}
My Resource hast a method defined this way...
#POST
#Produces(MediaType.APPLICATION_JSON)
#Consumes(MediaType.APPLICATION_JSON)
public Response doReservation(final ReservationDO reservationDO
, #QueryParam("serviceType") final String serviceType) {
...
}
The JSON shall be deserialized in this class:
#XmlRootElement
public class ReservationDO<T extends TargetPoi>
{
public String requestId;
public String startTime;
public String endTime;
public String serviceType;
public T targetPoi;
...
}
How can I tell Jackson to bind the JSON for the targetPoi properly to the correct subtype (TargetSub1Poi)? The serviceType could tell me to which subtype the targetPoi is to bind to...but I think this information can't be used from Jackson, does it? When I print out the deserialized JSON in th edoreservation method the oneMoreId part coming with the original JSON is lost.
Do I have to provide any TypeInfo or can I achieve it without?

Answer 1

It is possible to declare your parent class abstract and have a generic field. You just need to tell Jackson which sub-type to use to create an instance of you object. It can be done by using #JsonTypeInfo annotation as described at the Jackson polymorphic deserialization wiki page.
Here is an example:
public class JacksonPoi {
#JsonTypeInfo(use = JsonTypeInfo.Id.NAME,
include = JsonTypeInfo.As.PROPERTY, property = "type")
public static abstract class TargetPoi {
public String poiId;
}
#JsonTypeName("sub1")
public static class TargetSub1Poi extends TargetPoi {
public String oneMoreId;
#Override
public String toString() {
return "TargetSub1Poi{" +
"poiId='" + poiId + '\'' +
"oneMoreId='" + oneMoreId + '\'' +
'}';
}
}
#JsonTypeName("sub2")
public static class TargetSub2Poi extends TargetPoi {
public String twoMoreId;
#Override
public String toString() {
return "TargetSub2Poi{" +
"poiId='" + poiId + '\'' +
"twoMoreId='" + twoMoreId + '\'' +
'}';
}
}
public static class Bean<T extends TargetPoi> {
public String field;
public T poi;
#Override
public String toString() {
return "Bean{" +
"field='" + field + '\'' +
", poi=" + poi +
'}';
}
}
public static final String JSON = "{\n" +
"\"poi\": \n" +
"{\n" +
" \"type\": \"sub1\",\n" +
" \"poiId\": \"0000000602\",\n" +
" \"oneMoreId\": \"1\"\n" +
"},\n" +
"\"field\": \"value1\"\n" +
"}";
public static final String JSON2 = "{\n" +
"\"poi\": \n" +
"{\n" +
" \"type\": \"sub2\",\n" +
" \"poiId\": \"0000000602\",\n" +
" \"twoMoreId\": \"13\"\n" +
"},\n" +
"\"field\": \"value2\"\n" +
"}";
public static void main(String[] args) throws IOException {
ObjectMapper mapper = new ObjectMapper();
mapper.registerSubtypes(TargetSub1Poi.class, TargetSub2Poi.class);
Bean<TargetSub1Poi> poi1 = mapper.readValue(JSON, new TypeReference<Bean<TargetSub1Poi>>() {});
System.out.println(poi1);
Bean<TargetSub2Poi> poi2 = mapper.readValue(JSON2, new TypeReference<Bean<TargetSub2Poi>>() {});
System.out.println(poi2);
}
}
Output:
Bean{field='value1', poi=TargetSub1Poi{poiId='0000000602'oneMoreId='1'}}
Bean{field='value2', poi=TargetSub2Poi{poiId='0000000602'twoMoreId='13'}}