Convert Java object to JSON

JSON stands for JavaScript Object Notation that is a very small weighted format to store and transport data. The JSON format is very easy to understand because it has a self-describing nature. JSON is mainly used to transmit data between a server and a web application.

The details of an employee written in the JSON format looks like:

 {  
    "Employee": {  
        "name":       "Emma Watson",   
        "salary":      40000,   
        "married":    false  
    }  
}

Java object is an instance of a class or a self-contained component having properties and methods for making a certain type of data useful. Java object has a state, behavior and identity.

Java object of an employee is written in the following way:

//Defining an Employee class  
class Employee{  
	//Defining properties  
	String name;
	int salary;
	Boolean married;
	//creating main() method of teh Employee class  
	public static void main(String args[]){  
		//Creating object of Employee class  
		Employee emp =new Employee();
		emp.name = "Emma Watson";
		emp.salary = 40000;
		emp.married = false;
		//Printing values of the object  
		System.out.println(emp.name);  
		System.out.println(emp.salary);
		System.out.println(emp.married);
	}  
}  

Many times we need to convert Java objects into JSON so that we can easily understand them. To convert a Java object into a JSON object, we have the following two methods or way:

Using GSON library
Using Jackson API

Let's understand both of them one by one.

Using GSON library

The GSON library plays an important role in converting a Java object into JSON. GSON library not only converts Java object into JSON but also uses it to convert the JSON string into its equivalent Java object.

These are the following steps to convert a Java object into JSON:

Create a Maven project.
Add GSON dependency in xml file.
Create Plain Old Java Object to convert into JSON.
Create a Java class to convert the Java object to JSON.

Step 1: Create a Maven project

In the first step, we need to create a maven project using eclipse IDE. Converting Java objects into JSON is an advanced Java concept, so we recommend you to use an IDE like eclipse to easily understand the programs.

Step 2: Add GSON dependency in pom.xml

In the next step, we need to add the following GSON dependency in the pom.xml file to use the GSON library.

<dependency>   
<groupId>com.google.code.gson</groupId>   
<artifactId>gson</artifactId>   
<version>2.8.6</version>   
</dependency>  

After adding the dependency, the pom.xml file look like the following:

Step 3: Create POJO to convert into JSON

In the next step, we need to create a POJO, which we want to convert into a JSON object. In our example, we create a class MobilePhone with getter and setters for brand, name, ram, and rom.

MobilePhone.java

package javaTpoint.JavaObjectToJSON;
//Creating MobilePhone class
public class MobilePhone {
	//Creating properties of the class
	private String brand;  
	private String name;  
	private int ram;
	private int rom;
	//Setter and Getters
	public String getBrand() {
		return brand;
	}
	public void setBrand(String brand) {
		this.brand = brand;
	}
	public String getName() {
		return name;
	}
	public void setName(String name) {
		this.name = name;
	}
	public int getRam() {
		return ram;
	}
	public void setRam(int ram) {
		this.ram = ram;
	}
	public int getRom() {
		return rom;
	}
	public void setRom(int rom) {
		this.rom = rom;
	}
	Overriding the toString() method
	@Override  
	public String toString() {  
		// TODO Auto-generated method stub  
		return "\"MobilePhone [MobileBrand "+ brand + ", MobileName = " + name + ", RAM = " + ram + ", ROM = " + rom + "]";  
	}
}

Step 4: Create a Java class to convert the Java object into JSON

We need to create a new Java class that uses GSON to convert the MobilePhone object to JSON. In this class, we will create the getMobile() method. Inside the method, we set the values to the MobilePhone class's properties and return the MobilePhone object.

In the main method, we will create an object of the MobilePhone class and store the geMobile() method's returned value. After that, we will use the Gson().toJson() method to convert that object into a JSON object.

ConvertJSON.java

package JavaTpoint.JavaObjectToJSON;
import com.google.gson.Gson;  
public class ConvertJSON {
	public static MobilePhone getMobile(MobilePhone mobile) {  
		mobile.setBrand("SAMSUNG");  
		mobile.setName("J2 Core");  
		mobile.setRam(2);
		mobile.setRom(4);  
		return mobile;  
		} 
	public static void main(String[] args) {
		// TODO Auto-generated method stub
		MobilePhone mobilePhone = new MobilePhone();  
		mobilePhone = getMobile(mobilePhone);  
		System.out.println("The JSON representation of Object mobilePhone is ");  
		System.out.println(new Gson().toJson(mobilePhone));  
	}
}

When we run the ConvertJSON.java file, we will see the JSON object of the MobilePhone class object.

Using Jackson library

Jackson library is one of the simplest Java-based libraries. The Jackson library is used to serialize the Java object to JSON and vice versa. The ObjectMapper class of the Jackson API provides methods to convert the Java object to JSON format or object. The ObjectMapper class writeValueAsString() method takes the JSON object as a parameter and returns its respective JSON string.

These are the following steps to convert the Java object into a JSON object using Jackson API:

Create a Maven project
Add Jackson dependency to the pom.xml file.
Create a POJO object.
Create a new class to convert Java object to JSON object.

Step 1: Create a Maven project

In the first step, we need to create a maven project using eclipse IDE. Just like GSON, Jackson API is also supported by the Eclipse.

Step 2: Add Jackson dependency in pom.xml

In the next step, we need to add the following Jackson dependency in our pom.xml file to use the Jackson library.

<dependency>
     <groupId>com.fasterxml.jackson.core</groupId>
     <artifactId>jackson-databind</artifactId>
     <version>2.12.1</version>
</dependency>

Step 3: Create POJO to convert into JSON

In the next step, we need to create a POJO, which we want to convert into a JSON object. In this example, we create a class Product having getter and setters for the properties like id, name, and price.

Product.java

package JavaTpoint.JavaObjectToJSON;
//Creating Product class
public class Product {
	//Creating properties of Product class
	private int id;  
	private String name;  
	private int price;
	//Getter and Setters
	public int getId() {
		return id;
	}
	public void setId(int id) {
		this.id = id;
	}
	public String getName() {
		return name;
	}
	public void setName(String name) {
		this.name = name;
	}
	public int getPrice() {
		return price;
	}
	public void setPrice(int price) {
		this.price = price;
	}
	@Override  
	public String toString() {  
		// TODO Auto-generated method stub  
		return "\"Product [ProductId "+ id + ", ProductName = " + name + ", ProductPrice = " + price + "]";  
	}
}

Step 4: Create a Java class to convert the Java object into JSON

Just like our previous example of GSON, we will also create a new Java class ObjectToJson. Inside the method, we have created the getObjectData() method to set the values to the Product object and return that object of the Product class.

In the main() method, we have created an object of the Product class and the ObjectMapper class. After that, we will use the writeValueAsString() method of the ObjectMapper class to covert the Java object into a JSON object.

ObjectToJson.java

package JavaTpoint.JavaObjectToJSON;
import java.io.IOException;
import com.fasterxml.jackson.databind.ObjectMapper;
public class ObjectToJson {
	    public static void main(String[] a)
	    {
	        // Creating object of Product
	        Product product = new Product();
	        // Inserting the data into the object
	        product = getObjectData(product);
	        // Creating Object of ObjectMapper define in Jackson API
	        ObjectMapper Obj = new ObjectMapper();
	        try {
	            // Converting the Java object into a JSON string
	            String jsonStr = Obj.writeValueAsString(product);
	            // Displaying Java object into a JSON string
	            System.out.println(jsonStr);
	        }
	        catch (IOException e) {
	            e.printStackTrace();
	        }
	    }
	    // Getting data that we want to insert into an object
	    public static Product getObjectData(Product product)
	    {
	        // Insert the data
	    	product.setId(101);
	    	product.setName("Spark 131");
	    	product.setPrice(10000);
	        // Returning the product object
	        return product;
	    }
}

When we run the ObjectToJson.java file, we will see the JSON string of the Product class object.