json to Instant with a field "yyyy-MM-ddThh:mm:ss" using GSON but get java.lang.NumberFormatException: For input string: "1999-08-24T00:00:00"

Question

I am trying json parsing with gson in a small java applicaiton. I have a json string which comes from .Net business layer, has a field as "1999-08-24T00:00:00". In my model like User model, I have java.time.Instant birthDay field. With gson i am trying to get json string to my user model. Also I have a InstantDeserializer class. But when I try to convert it I got a message like java.lang.NumberFormatException.forInputString(NumberFormatException.java:65)..

Before the instant type I was using Date class. I wrote DateDeserializer class but I know Date class is deprecated. I googled to much page. I tried many things but i didn't how to figure out. So i just want to ask where I am making mistakes. What sould I do? How can I make my code more clear or what is the best approch? If you could give some code examples, I can understand better.

Any advice is appreciated..

Here is my code..

JSON String :

{
   "Value":{
      "ID":"123",
      "NAME":"John",
      "SURNAME":"Concept",
      "BIRTHDAY":"1999-08-24T00:00:00",
      "PAYMENTINFORMATION":[
         {
            "ID":"1",
            "PAYMENTINFO":"RECIEVED"
         }
      ]
   },
   "Succued": true
}

UserModel class

package Models;

import java.lang.reflect.Array;
import java.util.ArrayList;
import java.util.List;
import java.time.LocalDateTime;
import java.util.Date;
import com.google.gson.annotations.SerializedName;
import java.time.Instant;

public class UserModel {

    private long id;
    private String name;
    private String surname;
    private Instant birthday;
    private List<PaymentModel> paymentInformation;

    //GETTER SETTER

    public UserModel() {
        paymentInformation= new ArrayList<>();
    }
}

InstantDeserializer class

package Util;

import com.google.gson.JsonDeserializationContext;
import com.google.gson.JsonDeserializer;
import com.google.gson.JsonElement;
import com.google.gson.JsonParseException;
import java.lang.reflect.Type;
import java.time.Instant;
import java.time.LocalDateTime;
import java.time.ZoneId;

public class InstantDeSerializer implements JsonDeserializer<Instant> {

    @Override
    public Instant deserialize(JsonElement jelement, Type type, JsonDeserializationContext jdc) throws JsonParseException {
        Instant insObj= Instant.ofEpochMilli(jelement.getAsJsonPrimitive().getAsLong());
        return insObj;
    }

}

And Main class

public class JSONTryMe {
    public static void main(String[] args) throws Exception {

        JSONObject responseJSON = new JSONObject(jsonString);
        if (responseJSON.isNull("Value")) {
            return;
        }

        GsonBuilder build = new GsonBuilder();
        build.registerTypeAdapter(Instant.class, new InstantDeSerializer());
        Gson gObj = build.create();
        UserModel user = gObj.fromJson(responseJSON.getJSONObject("Value").toString(), UserModel.class);

        System.out.println(user.getBirthday().toString());    
    }
}

Ant the error stackTrace is

java.lang.NumberFormatException: For input string: "1999-08-24T00:00:00"
    at java.lang.NumberFormatException.forInputString(NumberFormatException.java:65)
    at java.lang.Long.parseLong(Long.java:589)
    at java.lang.Long.parseLong(Long.java:631)
    at com.google.gson.JsonPrimitive.getAsLong(JsonPrimitive.java:206)
    at Util.InstantDeSerializer.deserialize(InstantDeSerializer.java:25)
    at Util.InstantDeSerializer.deserialize(InstantDeSerializer.java:21)
    at com.google.gson.internal.bind.TreeTypeAdapter.read(TreeTypeAdapter.java:69)
    at com.google.gson.internal.bind.ReflectiveTypeAdapterFactory$1.read(ReflectiveTypeAdapterFactory.java:131)
    at com.google.gson.internal.bind.ReflectiveTypeAdapterFactory$Adapter.read(ReflectiveTypeAdapterFactory.java:222)
    at com.google.gson.Gson.fromJson(Gson.java:932)
    at com.google.gson.Gson.fromJson(Gson.java:897)
    at com.google.gson.Gson.fromJson(Gson.java:846)
    at com.google.gson.Gson.fromJson(Gson.java:817)
    at Source.JSONTryMe.main(JSONTryMe.java:85)

Answer 1

Here are several conceptual flaws:

• Birth dates should use LocalDate
• Your JSON input provides ISO datetime, but your deserializer tries to read milliseconds since epoch. Use LocalDate#parse() for this