GSON tutorials with code examples

Introduction

This post explains how to use GSON library in java.In my previous post I explained the process deserialization. Now lets see how to use google’s GSON library.Its one of the most popular libraries to manipulate JSON to java and vice versa.Gson uses reflection, so it does not require classes being serialized or de-serialized to be modified

GSON dependency:

Add below dependency in the application’s pom.xml . At the time of this post 2.8.6 was the latest version.Find the latest version here.

<dependency>
    <groupId>com.google.code.gson</groupId>
    <artifactId>gson</artifactId>
    <version>2.8.6</version>
  </dependency>

Code examples:

Json to Pojo :

In the below example, I am reading json as a string. And then using gson.fromJson method , I am converting it to a java object.

package com.codingbrains.gson;

import com.google.gson.Gson;
import java.nio.file.Files;
import java.nio.file.Paths;
import lombok.SneakyThrows;

/**
 * Reads JSON from file and parses it to a POJO
 */
public class jsonToPojo {

//SneakyThrows annotation will internally declare all checked exceptions.
  @SneakyThrows
  public static void main(String[] args) {
    //Read a Json from file and convert it to a string
    String strJson = new String(Files.readAllBytes(Paths.get("src/main/resources/json/Person.json")));
    //Create new GSON object
    Gson gson = new Gson();

    //Parse the JSON string to Person object
    Person person = gson.fromJson(strJson, Person.class);

    //Print required information from POJO
    System.out.println("Person Name is " + person.getName());
  }
}

Output:

Person Name is Dhoni

POJO to Json:

I have an object called Person . Using gson.toJson method , we can convert the POJO to a json.

package com.codingbrains.gson;

import com.google.gson.Gson;
import java.util.Arrays;
import java.util.List;

/**
 * Creates an object and then converts it to a JSON.
 * Uses GSON library
 */
public class PojoToJson {

  public static void main(String[] args) {
    //Create a Person object
    Person person = initializePerson();
    //Create a GSON object
    Gson gson = new Gson();
    //Convert Object to JSON string
    String strVirat = gson.toJson(person);
    //Print the result
    System.out.println(strVirat);

  }

  private static Person initializePerson() {
    Person virat = new Person();
    virat.setName("Virat Kohli");
    virat.setAge("30");
    virat.setPlace("Bangalore");
    virat.setTitle("Mr");
    List<String> hobbies = Arrays.asList("cricket", "Running", "travelling", "Sledging");
    virat.setMyHobbies(hobbies);
    return virat;

  }
}

Output:

{"name":"Virat Kohli","age":"30","place":"Bangalore","title":"Mr","myHobbies":["cricket","Running","travelling","Sledging"]}

How to Pretty print a json?

Whenever we print a json using gson library , it looks pretty ugly. To make it pretty we can enable setPrettyPrinting() on the gson object.

package com.codingbrains.gson;

import com.google.gson.Gson;
import com.google.gson.GsonBuilder;
import java.nio.file.Files;
import java.nio.file.Paths;
import java.util.Arrays;
import java.util.List;
import lombok.SneakyThrows;

public class PrettyPrintExample {
  //SneakyThrows annotation will internally declare all checked exceptions.
  @SneakyThrows
  public static void main(String[] args) {
    List<String> cars= Arrays.asList("Fiat","BMW","Lamborghini");
    //Create new GSON object
    Gson gson = new GsonBuilder().setPrettyPrinting().create();
    String prettyJson=gson.toJson(cars);
    System.out.println("pretty "+prettyJson);
  }
}

Output:

The output json looks pretty.

pretty [
"Fiat",
"BMW",
"Lamborghini"
]

Download this code:

You can download the code examples mentioned in this post from here.