Convert JSON Array to ArrayList in Java

In this guide, you will learn how to convert JSON array to ArrayList in Java. To parse the given JSON data, you can use org.json package of Java. Let’s start step by step guide:

1. Add the JSON Library: In order to parse the JSON data, make sure that you have org.json library in your project. In case you are using Maven, add the following dependency to your pom.xml:

<dependency>
    <groupId>org.json</groupId>
    <artifactId>json</artifactId>
    <version>20230227</version>
</dependency>

2. Parse the JSON Array and Convert to ArrayList: Let’s write the code to convert the JSON array to ArrayList.

import org.json.JSONArray;
import org.json.JSONObject;
import java.util.ArrayList;

public class JsonToArrayList {
    public static void main(String[] args) {
        // This is our JSON array contains name and age
        String jsonArrayString = "[{\"name\":\"Chaitanya\", \"age\":37}, {\"name\":\"Rahul\", \"age\":34}]";

        // Convert JSON array to JSONArray
        JSONArray jsonArray = new JSONArray(jsonArrayString);

        // Convert JSONArray to ArrayList
        ArrayList<JSONObject> arrayList = new ArrayList<>();
        for (int i = 0; i < jsonArray.length(); i++) {
            arrayList.add(jsonArray.getJSONObject(i));
        }

        // Print the ArrayList
        for (JSONObject obj : arrayList) {
            System.out.println(obj.toString());
        }
    }
}

Explanation:

• JSONArray and JSONObject belong to org.json package. You must include this package in your code.
• The jsonArrayString is the JSON array in string form.
• The object of JSONArray is created by passing jsonArrayString in the constructor of JSONArray class.
• The ArrayList that we have created is of JSONObject type, each element of this ArrayList represents the element of JSONArray.
• Finally, the ArrayList is printed which contains the same elements that are present in JSONArray.

Example with Custom Objects

If you want the ArrayList of custom objects as output then you need to create a custom class to map the JSON object. In previous example, the JSON array contain the person name and age data. Let’s create a custom class Person with name and age as instance variables to map JSON object.

import org.json.JSONArray;
import org.json.JSONObject;
import java.util.ArrayList;

class Person {
    private String name;
    private int age;

    // Constructor
    public Person(String name, int age) {
        this.name = name;
        this.age = age;
    }

    @Override
    public String toString() {
        return "Person{name='" + name + "', age=" + age + "}";
    }
}

public class JsonToArrayList {
    public static void main(String[] args) {
        // This is our JSON array contains name and age
        String jsonArrayString = "[{\"name\":\"Chaitanya\", \"age\":37}, {\"name\":\"Rahul\", \"age\":34}]";

        // Convert JSON array to JSONArray
        JSONArray jsonArray = new JSONArray(jsonArrayString);

        // Convert JSONArray to ArrayList of Person type
        ArrayList<Person> arrayList = new ArrayList<>();
        for (int i = 0; i < jsonArray.length(); i++) {
            JSONObject jsonObject = jsonArray.getJSONObject(i);
            String name = jsonObject.getString("name");
            int age = jsonObject.getInt("age");
            arrayList.add(new Person(name, age));
        }

        // Print the ArrayList
        for (Person person : arrayList) {
            System.out.println(person);
        }
    }
}