Custom deserialization in GSON?

Question

I need to create a custom deserializer so I can correctly deserialize a date that I'm receiving in this format: 2011-10-19T23:30:00-04:00. My Date object is one of many fields, contained one of many nested classes of the Object that I'm deserializing. Everything works fine except for the Date. My class looks like this:

public class OfferContainer{

    public Offer offer;

    public OfferContainer(){}   

    @Override
    public String toString()
    {
        return this.getID() +  offer.toString();
    }

    public String getDescription() {
        return offer.description;
    }

    public String getBusinessName() {
        return offer.business.name;
    }



    public class Offer
    {
        public Category category;
        public String description;
        public String discount;
        public Date expiration;
        public Date published;
        public String rescinded_at;
        public String title;
        public String hook;
        public Date valid_from;
        public Date valid_to;
        public String id;
        public Business business;
        public Location location;
        public String image_270x155;


        @Override
        public String toString()
        {
            return String.format(
                    "[Offer: category=%1$s, description=%2$s, discount=%3$s, expiration=%4$s, published=%5$s, rescinded_at=%6$s, title=%7$s, valid_from=%8$s, valid_to=%9$s, id=%10$s, business=%11$s, location=%12$s]",
                    category, description, discount, expiration, published, rescinded_at, title, valid_from, valid_to, id,
                    business, location);
        }

    }

   public enum Category
    {
        Salon, Spa, Restaurant, Other
    }



    public class Business
    {
        public String name;
        public String phone;
        public Address address;


        @Override
        public String toString()
        {
            return String.format(
                    "[Business: name=%1$s, phone=%2$s, address=%3$s]",
                    name, phone, address);
        }
    }


    public  class Address
    {
        public String address_1;
        public String address_2;
        public String city;
        public String cross_streets;
        public String state;
        public String zip;



        @Override
        public String toString()
        {
            return String.format(
                    "[Address: address_1=%1$s, address_2=%2$s, city=%3$s, cross_streets=%4$s, state=%5$s, zip=%6$s]",
                    address_1, address_2, city, cross_streets, state, zip);
        }
    }

    public class Location {
        public double latitude;
        public double longitude;



        public String toString() {
            return String.format("[Location: longitude=%1$s, latitude=%2$s]", longitude, latitude);
        }

    }

}

How do I use registerTypeAdapter in this scenario and how do I correctly implement a custom deserializer for this?

Thanks in advance!

Also, if it matters, here's how I'm actually getting my POJO:

  OfferContainer[] offers = gson.fromJson(json, OfferContainer[].class);

Here's the JSON:

{
    "offer":{
        "category":"Salon",
        "description":"Use this offer now to enjoy this great Salon at a 20% discount. ",
        "discount":"20",
        "expiration":"2011-04-08T02:30:00Z",
        "published":"2011-04-07T12:00:33Z",
        "rescinded_at":null,
        "title":"20% off at Jun Hair Salon",
        "valid_from":"2011-04-07T12:00:31Z",
        "valid_to":"2011-04-08T02:00:00Z",
        "id":"JUN_HAIR_1302177631",
        "business":{
            "name":"Jun Hair Salon",
            "phone":"2126192989",
            "address":{
                "address_1":"12 Mott St",
                "address_2":null,
                "city":"New York",
                "cross_streets":"Chatham Sq & Worth St",
                "state":"NY",
                "zip":"10013"
            }
        },
        "location":{
            "latitude":"40.714021",
            "longitude":"-73.998663"
        },
        "distance":619.8162766744034,
        "draws":[
            "Hair Cut",
            "Blow Dry",
            "Blow Dry Treatment"
        ],
        "claim_link":"http://m-s.com/offers/JUN_HAIR_1302177631?app_id=SavIMg",
        "mobile_claim_link":"http://m-s.com/offers/JUN_HAIR_1302177631?app_id=SavIMg"
    }
}

Answer 1

You need to implement JSONDeserializer<OfferContainer> and then override the deserialize method to achieve this. Have a look at this SO question GSON deserializing key-value to custom object

You can also try setting the dateformat in the GsonBuilder like this

 Gson gson = new GsonBuilder()
     .setDateFormat("yyyy-MM-dd'T'HHmmss.SSS'Z'")
     .create();
 OfferContainer [] offers = gson.fromJson(json, OfferContainer[].class);