Convert JSON String to POJO Class Object in Java

In this tutorial, we will show you two different methods to convert JSON String to a Java POJO Class object:

Using ObjectMapper

ObjectMapper provides methods for reading and writing JSON, either to and from basic POJOs (Plain Old Java Objects), or to and from a general-purpose JSON Tree Model (JsonNode), as well as related functionality for performing conversions.

To use ObjectMapper class, you need to install jackson-databind dependency to your project.

In a Spring Boot project, the jackson-databind dependency is by default included in spring-boot-starter-web starter library. The Jackson version included that comes with Spring Boot starter library allows you to write read/write JSON data. However, it is a good practice to specify this dependency because Spring update could change the functionality.

Let the JSON string that we need to convert to a Java Class object be as follows:

"{  
    \"id\": 1,
    \"firstName\": \"Danny\",
    \"lastName\": \"Brown\",
    \"active\": true
}"    

To convert the above data into a Java Class object, do the following:

1. Create a Java POJO class with fields whose names exactly match to the JSON key names:

public class User {
	private int id;
	private String firstName;
	private String lastName;
	private boolean active;

	public int getId() {
		return id;
	}

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

	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 boolean isActive() {
		return active;
	}

	public void setActive(boolean active) {
		this.active = active;
	}

}

2. Create an object of ObjectMapper class and use the readValue() method to convert JSON String data into a Java class object as shown in the example below:

import com.fasterxml.jackson.core.JsonProcessingException;
import com.fasterxml.jackson.databind.JsonMappingException;
import com.fasterxml.jackson.databind.ObjectMapper;

public class Example {

	public static void main(String[] args) {
		// example json string data
		String jsonStringExampleData = "{\"id\":1,\"firstName\":\"Danny\", \"lastName\":\"Brown\", \"active\":true}";

		// creating an object of ObjectMapper
		ObjectMapper objectMapper = new ObjectMapper();

		try {
			// converting from JSON string to Class object
			User user = objectMapper.readValue(jsonStringExampleData, User.class);

			// printing output
			System.out.println("Id = " + user.getId());
			System.out.println("First name = " + user.getFirstName());
			System.out.println("Last name = " + user.getLastName());
			System.out.println("Active = " + user.isActive());
		} catch (JsonMappingException e) {
			e.printStackTrace();
		} catch (JsonProcessingException e) {
			e.printStackTrace();
		}

	}

}

Using Gson Library

1. Add Gson dependency to your project.
2. Next, you can create an object of Gson and use fromJson() method to convert JSON String to POJO Class object as shown in the example below:

import com.google.gson.Gson;

public class Example {

	public static void main(String[] args) {
		// example json string data
		String jsonStringExampleData = "{\"id\":1,\"firstName\":\"Danny\", \"lastName\":\"Brown\", \"active\":true}";

		// creating an object of Gson
		Gson gson = new Gson();

		// converting from json string to User class object
		User user = gson.fromJson(jsonStringExampleData, User.class);
		
		// printing output
		System.out.println("Id = " + user.getId());
		System.out.println("First name = " + user.getFirstName());
		System.out.println("Last name = " + user.getLastName());
		System.out.println("Active = " + user.isActive());
	}

}