How to Convert Java POJO to JSON Using Jackson Library

JSON or JavaScript Object Notation has become a fundamental component in modern programming, enabling easy data interchange between systems. In Java, handling JSON involves various libraries, and one of the most popular ones is Jackson.

In this guide, we'll explore how to leverage the Jackson library to convert Java objects to JSON effortlessly.

What is Jackson Library

Jackson is a Java-based library designed to serialize Java objects to JSON and vice versa. It provides robust functionality for converting objects to JSON strings and parsing JSON back into Java objects. With Jackson, developers can seamlessly integrate JSON handling into their Java applications.

Converting Java Object to JSON

The key class in Jackson for converting Java objects to JSON is ObjectMapper. This class provides methods to perform serialization. Here's a step-by-step guide to converting a Java object to JSON using Jackson:

Add Jackson Dependency – Begin by adding the Jackson dependency to your project's pom.xml file:

<dependency>
    <groupId>com.fasterxml.jackson.core</groupId>
    <artifactId>jackson-databind</artifactId>
    <version>2.10.0.pr2</version>
</dependency>

Create a Java Bean (POJO) – Define a Java class with private variables and corresponding getter and setter methods. This class represents the structure of the object you want to convert to JSON.

Instantiate ObjectMapper – Create an instance of the ObjectMapper class provided by Jackson.

Convert Object to JSON – Use the writeValueAsString() method of the ObjectMapper class to convert the Java object to a JSON string.

Implementation

Let's consider a simple example where we have a Student class with attributes like id, name, age, and phone. We'll convert an instance of this class to JSON.

import com.fasterxml.jackson.databind.ObjectMapper;

public class JacksonExample {
    public static void main(String[] args) throws Exception {
        Student student = new Student();
        student.setId(001);
        student.setName("Krishna");
        student.setAge(30);
        student.setPhone(9848022338L);

        // Creating the ObjectMapper object
        ObjectMapper mapper = new ObjectMapper();

        // Converting the Object to JSONString
        String jsonString = mapper.writeValueAsString(student);
        System.out.println(jsonString);
    }
}

Output:

{"id":1, "name":"Krishna", "age":30, "phone":9848022338}

If you want to pretty print the JSON of the instance of java class, you can use the method writerWithDefaultPrettyPrinter() of the ObjectMapper, like this.

// ...
// Converting the Object to JSONString
   String jsonString = mapper.writerWithDefaultPrettyPrinter().writeValueAsString(student);
   System.out.println(jsonString);
// ...

Output:

{
	"id":1,
	"name":"Krishna",
	"age":30,
	"phone":9848022338
}

Ending

In conclusion, the Jackson library simplifies the process of converting Java objects to JSON strings. By following the steps outlined in this guide, developers can seamlessly integrate JSON serialization into their Java applications, facilitating efficient data interchange between systems.