Convert POJO Class Object to JSON String in Java

In this tutorial, we will show you two different ways for converting POJO Class object to JSON string in Java:

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 POJO Class that we need to convert to a JSON string be as follows:

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;
	}

}

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

public class Example {

	public static void main(String[] args) {
		User user = new User();
		user.setId(1);
		user.setFirstName("Danny");
		user.setLastName("Brown");
		user.setActive(true);

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

		// converting from pojo class object to json string
		String jsonString = "";
		try {
			jsonString = objectMapper.writeValueAsString(user);
		} catch (JsonProcessingException e) {
			e.printStackTrace();
		}
		System.out.println("User = " + jsonString);
	}

}

Using Gson Library

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

import com.google.gson.Gson;

public class Example {

	public static void main(String[] args) {
        //creating pojo class object with data
		User user = new User();
		user.setId(1);
		user.setFirstName("Danny");
		user.setLastName("Brown");
		user.setActive(true);

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

		// converting from pojo class object to json string
		String jsonStringData = gson.toJson(user);

		// printing output
		System.out.println("User = " + jsonStringData);

	}

}