How to Convert JSON Array Object to Java Object?

JSON arrays are useful for storing multiple values together that are related or part of the same set. For example, storing a list of items, user profiles, product catalog, etc. JSON arrays allow ordered access to the values using indices like in regular arrays in other languages (0 indexed).

Conversion Methods:

• Using a JSON parsing library: Jackson & GSON
• Iterating and parsing manually.

Steps to Convert JSON Array Object to Java Object

Below are the steps and implementation to convert JSON Array object to Java object using Jackson library.

Step 1: Create a Maven Project

Open any preferred IDE and create a new Maven project. Here we will be using IntelliJ IDEA, we can do this by selecting File -> New -> Project.. -> Maven and following the wizard.

Step 2: Add Jackson Dependency to POM.xml

Now, we will add Jackson dependency to the pom.xml file.

XML

<?xml version="1.0" encoding="UTF-8"?>
<project xmlns="http://maven.apache.org/POM/4.0.0"
         xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
         xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 http://maven.apache.org/xsd/maven-4.0.0.xsd">
    <modelVersion>4.0.0</modelVersion>

    <groupId>org.example</groupId>
    <artifactId>Java-Object</artifactId>
    <version>1.0-SNAPSHOT</version>
    <dependencies>
        <dependency>
            <groupId>com.fasterxml.jackson.core</groupId>
            <artifactId>jackson-databind</artifactId>
            <version>2.13.0</version> <!-- Use the latest version available -->
        </dependency>

    </dependencies>
    <properties>
        <maven.compiler.source>21</maven.compiler.source>
        <maven.compiler.target>21</maven.compiler.target>
        <project.build.sourceEncoding>UTF-8</project.build.sourceEncoding>
    </properties>

</project>

Step 3: Create the Java POJO Class

The User class defines a POJO to map JSON data with name and age properties. Getters and setters are provided for Jackson to populate objects.

User.java

Java

package org.example;

public class User
{
    private String firstName;
    private String lastName;

    private String email;

    public User() {}
    // Constructor Declaration
    public User(String firstName, String lastName,
                String email)
    {
        this.firstName = firstName;
        this.lastName = lastName;
        this.email = email;
    }
    // generate getters and setters
    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 String getEmail()
    {
      return email;
    }

    public void setEmail(String email)
    {
        this.email = email;
    }
}

Step 4: In the Main class add logic of Conversion JSON Array Object to Java Object

Now, we will add the logic to convert JSON Array Object to Java Object in the main class.

Java

package org.example;

import com.fasterxml.jackson.databind.ObjectMapper;

public class Main {
    public static void main(String[] args)
    {
        try {
            // JSON string representing an array of user objects
            String jsonString = "[{\"firstName\":\"User1\",\"lastName\":\"XYZ\",\"email\":\"user1@example.com\"},"
                  + "{\"firstName\":\"User2\",\"lastName\":\"PQR\",\"email\":\"user2@example.com\"}]";

            // Create an ObjectMapper instance
            ObjectMapper objectMapper = new ObjectMapper();

            // Deserialize the JSON string into an array of User objects
            User[] users = objectMapper.readValue(jsonString, User[].class);

            // Print the details of each user
            for (User user : users) {
                System.out.println(
                    "First Name: " + user.getFirstName()
                    + ", Last Name: " + user.getLastName()
                    + ", Email: " + user.getEmail());
            }
        }
        catch (Exception e) {
            e.printStackTrace();
        }
    }
}

Output:

First Name: User1, Last Name: XYZ, Email: user1@example.com
First Name: User2, Last Name: PQR, Email: user2@example.com

Explanation of the Code:

• In the above code, we have a JSON string jsonString representing an array of user objects.
• We have created an ObjectMapper instance from the Jackson library, which helps with JSON processing.
• We have used the readValue() method of the ObjectMapper to convert the JSON string into an array of User objects. We specify the type of the target array using User class.
• Then we iterate over the array of User objects and print the details of each user.