GSON - Null Object Support

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Gson by default generates optimized JSON content ignoring the NULL values. But GsonBuilder provides flags to show NULL values in the JSON output using the GsonBuilder.serializeNulls() method.

GsonBuilder builder = new GsonBuilder(); 
builder.serializeNulls(); 
Gson gson = builder.create(); 

Example without serializeNulls Call

package net.javaguides.gson;

import com.google.gson.Gson;
import com.google.gson.GsonBuilder;

/**
 * 
 * @author Ramesh Fadatare
 *
 */
public class GSONNullSupport {
    public static void main(String[] args) {
        Gson gson = new GsonBuilder().setPrettyPrinting().create();

        User user = new User();
        user.setId(100);
        user.setLastName("Fadatare");
        user.setAge(28);

        String userJson = gson.toJson(user);
        System.out.println(userJson);
    }
}

class User {

    private int id;
    private String firstName;
    private String lastName;
    private int age;
    private String gender;
    private String password;

    public int getId() {
        return id;
    }

    public void setId(int i) {
        this.id = i;
    }

    public String getFirstName() {
        return firstName;
    }

    public void setFirstName(String firstName) {
        this.firstName = firstName;
    }

    public String getLastName() {
        return lastName;
    }

    public void setLastName(String lastName) {
        this.lastName = lastName;
    }

    public int getAge() {
        return age;
    }

    public void setAge(int age) {
        this.age = age;
    }

    public String getGender() {
        return gender;
    }

    public void setGender(String gender) {
        this.gender = gender;
    }

    public String getPassword() {
        return password;
    }

    public void setPassword(String password) {
        this.password = password;
    }

    @Override
    public String toString() {
        return "User [id=" + id + ", firstName=" + firstName + ", lastName=" + lastName + ", age=" + age + ", gender=" +
            gender + "]";
    }
}

Output:

{
  "id": 100,
  "lastName": "Fadatare",
  "age": 28
}

Note that in the above JSON, the fields id, lastName, and gender are ignored because these fields were not set to null in the User object.

Example with a serializeNulls call

package net.javaguides.gson;

import com.google.gson.Gson;
import com.google.gson.GsonBuilder;

/**
 * 
 * @author Ramesh Fadatare
 *
 */
public class GSONNullSupport {
    public static void main(String[] args) {
        GsonBuilder builder = new GsonBuilder();
        builder.serializeNulls();
        builder.setPrettyPrinting();
        Gson gson = builder.create();

        User user = new User();
        user.setId(100);
        user.setLastName("Fadatare");
        user.setAge(28);

        String userJson = gson.toJson(user);
        System.out.println(userJson);

        User user2 = gson.fromJson(userJson, User.class);
        System.out.println(user2);
    }
}

class User {

    private int id;
    private String firstName;
    private String lastName;
    private int age;
    private String gender;
    private String password;

    public int getId() {
        return id;
    }

    public void setId(int i) {
        this.id = i;
    }

    public String getFirstName() {
        return firstName;
    }

    public void setFirstName(String firstName) {
        this.firstName = firstName;
    }

    public String getLastName() {
        return lastName;
    }

    public void setLastName(String lastName) {
        this.lastName = lastName;
    }

    public int getAge() {
        return age;
    }

    public void setAge(int age) {
        this.age = age;
    }

    public String getGender() {
        return gender;
    }

    public void setGender(String gender) {
        this.gender = gender;
    }

    public String getPassword() {
        return password;
    }

    public void setPassword(String password) {
        this.password = password;
    }

    @Override
    public String toString() {
        return "User [id=" + id + ", firstName=" + firstName + ", lastName=" + lastName + ", age=" + age + ", gender=" +
            gender + "]";
    }
}

Output:

{
  "id": 100,
  "firstName": null,
  "lastName": "Fadatare",
  "age": 28,
  "gender": null,
  "password": null
}
User [id=100, firstName=null, lastName=Fadatare, age=28, gender=null]

Reference

GSON User Guide

GSON Java DOC

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Google GSON Tutorial

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