Custom date serialization - Object to JSON (GSON & example)

Given the user defined object or POJO, having Date field, we would like to serialize the POJO to JSON.
During serialization, we would like save Date as timestamp.
We will use the Google gson library to achieve the POJO to JSON conversion and vice versa.
We will create Person class and we will perform the following operations with Person class
1. Convert Person Object to JSON string
  - Serialize the date as timestamp
2. Convert the JSON string to corresponding person object
  - DeSerialize the timestamp as Date

GSON maven dependency:

<dependency>
    <groupId>com.google.code.gson</groupId>
    <artifactId>gson</artifactId>
    <version>2.5</version>
</dependency>

Program – Date to / from timestamp conversion (POJO <->JSON)

1.) Person Class:

The person class containing date data member.
We have overloaded toString method to print person information.

package org.learn.gson;
import java.util.Date;
 
public class Person {
    public String firstName;
    public String lastName;
    public Date date;
    public String contact;
    public Person(String firstName, String lastName,
                Date date, String contact) {
        this.firstName = firstName;
        this.lastName = lastName;
        this.date = date;
        this.contact = contact;
    }
    public String toString() {
        return "[" + firstName + " " + lastName +
               " \"" + date.toString() + "\" " +contact +"]";
    }
}

2.) Date2Json Class:

Date2Json is responsible for performing following operations.

Convert person object to JSON (serialization).
- We have written custom DateSerializer class, to serialize date as timestamp.
Convert JSON to person object (Deserialization).
- We have written custom DateSerializer class, to deserialize timestamp as Date.

package org.learn.gson;
import java.lang.reflect.Type;
import java.util.Date;
 
import com.google.gson.Gson;
import com.google.gson.GsonBuilder;
import com.google.gson.JsonDeserializationContext;
import com.google.gson.JsonDeserializer;
import com.google.gson.JsonElement;
import com.google.gson.JsonParseException;
import com.google.gson.JsonPrimitive;
import com.google.gson.JsonSerializationContext;
import com.google.gson.JsonSerializer;
import com.google.gson.reflect.TypeToken;
 
class DateDeserializer implements JsonDeserializer {
         
    public Date deserialize(JsonElement json, Type typeOfT,
                                    JsonDeserializationContext context)
            throws JsonParseException {
        return json == null ? null : new Date(json.getAsLong());
    }
}
 
class DateSerializer implements JsonSerializer {    
    public JsonElement serialize(Date date, Type typeOfSrc,
                                    JsonSerializationContext context) {
        return date == null ? null : new JsonPrimitive(date.getTime());
    }
}
 
public class Date2Json {
    public static void main(String[] args) {
        GsonBuilder gson = new GsonBuilder();
        gson.registerTypeAdapter(Date.class, new DateDeserializer());
        gson.registerTypeAdapter(Date.class, new DateSerializer());
         
        Gson objGson = gson.setPrettyPrinting().create();
        Person objPerson = new Person("Mike","harvey",new Date(),"00186");
        // Convert Person object to json
        String json = objGson.toJson(objPerson);
        System.out.println("1. Convert Person object to Json");
        System.out.println(json);
 
        // Convert to json to person object
        Type listType = new TypeToken() {}.getType();
        System.out.println("2. Convert JSON to person object");
        Person objFromJson = objGson.fromJson(json, listType);
        System.out.println(objFromJson);
    }
}

Download Sample Code – GSON Object to JSON

Output – Date serialization & deserialization (POJO <-> JSON)

1. <strong>Convert Person object to Json</strong>
{
"firstName": "Mike",
"lastName": "harvey",
<strong>"date": 1454426955623,</strong>
"contact": "00186"
}
2. <strong>Convert JSON to person object</strong>
[Mike harvey <strong>"Tue Feb 02 20:59:15 IST 2016" </strong>00186]

GSON maven dependency:

Program – Date to / from timestamp conversion (POJO <->JSON)

1.) Person Class:

2.) Date2Json Class:

Output – Date serialization & deserialization (POJO <-> JSON)

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