JsonMappingException while deserializing Object from mongodb by jackson lib

I have documents saved in mongodb and Im fetching data as I show below. I am deserializing DBObject(json string) to object by jackson. However Im getting this exception org.codehaus.jackson.map.JsonMappingException: Can not deserialize instance of java.util.Date out of START_OBJECT token. The date field is like that in the json string. Any help would be appreciated.

"eventStartDate" : { "$date" : "2015-02-27T21:48:04.452Z"}

BasicDBObject bdo = new BasicDBObject("$near", location);
        bdo.put("$maxDistance", 100);
        bdo.put("$minDistance", 1);

        final BasicDBObject query = new BasicDBObject("event.address.location", bdo);

        List<Events> ads = mo.execute("evt", new CollectionCallback<List<Events>>() {
            @Override
            public List<Events> doInCollection(DBCollection collection) throws MongoException, DataAccessException {
                DBCursor c = collection.find(query);
                ObjectMapper oom = new ObjectMapper();
                List<Events> ads = new ArrayList<Events>();
                for(DBObject dos : c){
                    Events a = null;
                    try {
                        a = oom.readValue(dos.toString(), Events.class);
                        ads.add(a);
                    } catch (Exception e) {
                        logger.error(e);
                    } 
                }
                return ads;
            }
        });