Convert /Serialize array of objects to / from json in java (Gson /example)

• Given an array of user defined objects , we need to convert array of POJOs to JSON String.
  • Also, we will convert the JSON String to array of POJOs.
• We will use the Google gson library for serialization and deserialization process.
• We will create Person class and we will perform the following operations with Person class
  • Convert Person[] array to JSON string
  • Convert the JSON string to Person[] array

GSON Maven dependency:

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

Program – Convert/ Serialize array of objects to/from json (Gson & example)

1.) Person Class:

• Person class containing firstName, lastName, age etc.
• We have overloaded toString method to print person information.

package org.learn.gson;
public class Person {
	public String firstName;
	public String lastName;
	public int age;
	public String contact;
	public Person(String firstName, String lastName,
				int age, String contact) {
		this.firstName = firstName;
		this.lastName = lastName;
		this.age = age;
		this.contact = contact;
	}
	public String toString() {
	    return "[" + firstName + " " + lastName +
		       " " + age + " " +contact +"]";
	}
}

2.) JSONArrayConverter Class:

JSONArrayConverter is responsible for performing following operations.

1. Convert Person[] array to JSON string
2. Convert the JSON string to Person[] array

package org.learn.gson;
import java.util.Arrays;
import java.util.stream.Stream;

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

public class JSONArrayConverter 
{
    public static void main( String[] args )
    {
    	Gson objGson = new GsonBuilder().setPrettyPrinting().create();
    	    
    	Person[] personList = Stream.of(
				new Person("Mike", "harvey", 34, "001894536"),
			  	new Person("Nick", "young", 75,  "005425676"),
				new Person("Jack", "slater", 21 ,"009654153"),
				new Person("gary", "hudson", 55,"00564536"))
				.toArray(Person[]::new);
    	//Array to JSON
    	String mapToJson = objGson.toJson(personList);
    	System.out.println("1. Person array to JSON conversion is : \n");
    	System.out.println(mapToJson);
    	
    	//JSON to Array
    	Person[] arrayPerson = objGson.fromJson(mapToJson, Person[].class);
    	System.out.println("2. JSON to Array of persons conversion is :\n");
    	Arrays.stream(arrayPerson).forEach(System.out::println);
    }
}

Download code – Serialize array of objects to/from JSON (GSON)

Output – convert array of objects to/from json (Gson & example)

1. Person array to JSON conversion is :

[
{
"firstName": "Mike",
"lastName": "harvey",
"age": 34,
"contact": "001894536"
},
{
"firstName": "Nick",
"lastName": "young",
"age": 75,
"contact": "005425676"
},
{
"firstName": "Jack",
"lastName": "slater",
"age": 21,
"contact": "009654153"
},
{
"firstName": "gary",
"lastName": "hudson",
"age": 55,
"contact": "00564536"
}
]
2. JSON to Array of persons conversion is :

[Mike harvey 34 001894536]
[Nick young 75 005425676]
[Jack slater 21 009654153]
[gary hudson 55 00564536]