How to create JSON Array Payload using POJO – Jackson API

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In the previous tutorial, I have explained the creation of JSON Object using POJO. In this tutorial, will create a JSON Array Payload using POJO.

To know about POJO, please refer to this tutorial.

You can refer these tutorials to understand various ways of using Jackson API

Serialization – How to create JSON Payload from Java Object – Jackson API

How to create JSON Array Payload using POJO – Jackson API

How to create Nested JSON Object using POJO – Jackson API

Serialization – How to convert Map to JSON string using Jackson API

JSON Array is a collection of JSON Objects. In the below example, will create a list of employees.

The sample JSON Array structure looks like the image as shown below:-

{
  "firstName" : "Vibha",
  "lastName" : "Singh",
  "age" : 30,
  "salary" : 75000.0,
  "designation" : "Manager",
  "contactNumber" : "+919999988822",
  "emailId" : "abc@test.com"
  
  "firstName" : "Neha",
  "lastName" : "Verma",
  "age" : 25,
  "salary" : 60000.0,
  "designation" : "Lead",
  "contactNumber" : "+914442266221",
  "emailId" : "xyz@test.com"
  
  "firstName" : "Rajesh",
  "lastName" : "Gupta",
  "age" : 20,
  "salary" : 40000.0,
  "designation" : "Intern",
  "contactNumber" : "+919933384422",
  "emailId" : "pqr@test.com"
}

We need to create an Employee class that contains private data members and corresponding getter and setter methods of these data members.

Below is an Employee Class with private data members, as well as the corresponding getter and setter methods of these data members. Every IDE provides a shortcut to create these getter and setter methods.

public class Employee {

	// private variables or data members of POJO class
	private String firstName;
	private String lastName;
	private int age;
	private double salary;
	private String designation;
	private String contactNumber;
	private String emailId;

	// Getter and setter methods
	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 int getAge() {
		return age;
	}

	public void setAge(int age) {
		this.age = age;
	}

	public double getSalary() {
		return salary;
	}

	public void setSalary(double salary) {
		this.salary = salary;
	}

	public String getDesignation() {
		return designation;
	}

	public void setDesignation(String designation) {
		this.designation = designation;
	}

	public String getContactNumber() {
		return contactNumber;
	}

	public void setContactNumber(String contactNumber) {
		this.contactNumber = contactNumber;
	}

	public String getEmailId() {
		return emailId;
	}

	public void setEmailId(String emailId) {
		this.emailId = emailId;
	}

}

Serialization – Serialization is a process where you convert an Instance of a Class (Object of a class) into a Byte Stream. Here, we are converting Employee class object to JSON Array representation or Object.

Deserialization – It is the reverse of serializing. In this process, we will read the Serialized byte stream from the file and convert it back into the Class instance representation. Here, we are converting a JSON Array to an Employee class object.

We are using Jackson API for Serialization and Deserialization. So, add the Jackson dependency to the project.

<!-- https://mvnrepository.com/artifact/com.fasterxml.jackson.core/jackson-databind -->
<dependency>
    <groupId>com.fasterxml.jackson.core</groupId>
    <artifactId>jackson-databind</artifactId>
    <version>2.13.0</version>
</dependency>

Below is the class where we will assign values to the data members by using getter methods (Serialization).

public class EmployeeArrayTest {

	@Test
	public void createEmployeeArray() {

		Employee emp1 = new Employee();
		emp1.setFirstName("Vibha");
		emp1.setLastName("Singh");
		emp1.setAge(30);
		emp1.setSalary(75000);
		emp1.setDesignation("Manager");
		emp1.setContactNumber("+919999988822");
		emp1.setEmailId("abc@test.com");

		Employee emp2 = new Employee();
		emp2.setFirstName("Neha");
		emp2.setLastName("Verms");
		emp2.setAge(35);
		emp2.setSalary(60000);
		emp2.setDesignation("Lead");
		emp2.setContactNumber("+914442266221");
		emp2.setEmailId("xyz@test.com");

		Employee emp3 = new Employee();
		emp3.setFirstName("Rajesh");
		emp3.setLastName("Gupta");
		emp3.setAge(20);
		emp3.setSalary(40000);
		emp3.setDesignation("Intern");
		emp3.setContactNumber("+919933384422");
		emp3.setEmailId("pqr@test.com");

		// Creating a List of Employees
		List<Employee> employeeList = new ArrayList<Employee>();
		employeeList.add(emp1);
		employeeList.add(emp2);
		employeeList.add(emp3);

		// Converting a Java class object to a JSON Array Payload as string
		ObjectMapper mapper = new ObjectMapper();
		try {
			String allEmployeeJson = mapper.writeValueAsString(employeeList);
			String employeeListPrettyJson = mapper.writerWithDefaultPrettyPrinter().writeValueAsString(employeeList);
			System.out.println(allEmployeeJson);
			System.out.println(employeeListPrettyJson);
		} catch (JsonProcessingException e) {
			e.printStackTrace();
		}
	}

ObjectMapper is imported from:-

import com.fasterxml.jackson.databind.ObjectMapper;

In the below example, we are deserializing the JSON Array Payload to Java objects.

    @Test
	public void getEmployeeArray() {

		Employee emp1 = new Employee();
		emp1.setFirstName("Vibha");
		emp1.setLastName("Singh");
		emp1.setAge(30);
		emp1.setSalary(75000);
		emp1.setDesignation("Manager");
		emp1.setContactNumber("+919999988822");
		emp1.setEmailId("abc@test.com");

		Employee emp2 = new Employee();
		emp2.setFirstName("Neha");
		emp2.setLastName("Verms");
		emp2.setAge(35);
		emp2.setSalary(60000);
		emp2.setDesignation("Lead");
		emp2.setContactNumber("+914442266221");
		emp2.setEmailId("xyz@test.com");

		Employee emp3 = new Employee();
		emp3.setFirstName("Rajesh");
		emp3.setLastName("Gupta");
		emp3.setAge(20);
		emp3.setSalary(40000);
		emp3.setDesignation("Intern");
		emp3.setContactNumber("+919933384422");
		emp3.setEmailId("pqr@test.com");

		// Creating a List of Employees
		List<Employee> employeeList = new ArrayList<Employee>();
		employeeList.add(emp1);
		employeeList.add(emp2);
		employeeList.add(emp3);

		// Converting a Java class object to a JSON Array Payload as string

		ObjectMapper mapper = new ObjectMapper();
		String allEmployeeJson = null;

		try {
			allEmployeeJson = mapper.writerWithDefaultPrettyPrinter().writeValueAsString(employeeList);
		} catch (JsonProcessingException e) {
			e.printStackTrace();
		}

		List<Employee> allEmployeeDetails = null;
		try {
			allEmployeeDetails = mapper.readValue(allEmployeeJson, new TypeReference<List<Employee>>() {
			});
		} catch (JsonMappingException e) {
			e.printStackTrace();
		} catch (JsonProcessingException e) {
			e.printStackTrace();
		}

		for (Employee emp : allEmployeeDetails) {

			System.out.println("===================================");

			System.out.println("First Name of employee : " + emp.getFirstName());
			System.out.println("Last Name of employee : " + emp.getLastName());
			System.out.println("Age of employee : " + emp.getAge());
			System.out.println("Salary of employee : " + emp.getSalary());
			System.out.println("Designation of employee : " + emp.getDesignation());
			System.out.println("Contact Number of employee : " + emp.getContactNumber());
			System.out.println("EmailId of employee : " + emp.getEmailId());
		}
	}

If you want to read the data from a file placed on Desktop, below is the sample code for the same.

@Test
	public void readArrayJsonFromFile() throws IOException {

		ObjectMapper mapper = new ObjectMapper();

		// Converting Employee json string to Employee class object
		List<Employee> allEmployeeDetails = null;
		try {
			allEmployeeDetails = mapper.readValue(new File(
					"C:\\Users\\Vibha\\Desktop\\EmployeeList.json"),
					new TypeReference<List<Employee>>() {
					});
		} catch (StreamReadException e) {
			e.printStackTrace();
		} catch (DatabindException e) {
			e.printStackTrace();
		} catch (IOException e) {
			e.printStackTrace();
		}


		for (Employee emp : allEmployeeDetails) {

			System.out.println("######################################");

			System.out.println("First Name of employee : " + emp.getFirstName());
			System.out.println("Last Name of employee : " + emp.getLastName());
			System.out.println("Age of employee : " + emp.getAge());
			System.out.println("Salary of employee : " + emp.getSalary());
			System.out.println("Designation of employee : " + emp.getDesignation());
			System.out.println("Contact Number of employee : " + emp.getContactNumber());
			System.out.println("EmailId of employee : " + emp.getEmailId());
		}
	}

We are done! Congratulations on making it through this tutorial and hope you found it useful! Happy Learning!!

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