Deserialize to Collection/Array in Jackson

Deserializing the JSON Array to a Java Array or Collection is one of the most important tasks when we work with APIs in Java. We can easily deserialize the JSON Array into Java Array or Collection by using Jackson.

Let's understand how we can deserialize the JSON array into both the Java Array and the Collection one by one:

Deserialize JSON Array to Java Array

We can easily deserialize JSON Array into Java Array by using the readValue() method of the ObectMapper class. In the readValue() method, we pass two parameters, i.e., jsonString and Student[].class.

Let's take an example to understand how we can deserialize JSON Array into Java Array by using ObjectMapper class:

DeserializeJSONArrayToJavaArrayExample.java

// import required classes and package if any
import java.util.ArrayList;
import java.util.List;
import java.util.Scanner;
import com.fasterxml.jackson.core.JsonProcessingException;
import com.fasterxml.jackson.databind.ObjectMapper;

public class DeserializeJSONArrayToJavaArrayExample {
	
	//main() method start()
	public static void main(String args []) throws JsonProcessingException {
	
		int n;
		
		// create an instance of ObjectMapper class
		ObjectMapper mapper = new ObjectMapper();
		
		// create Scanner class object
		Scanner sc = new Scanner(System.in);
		
		// create an empty list of Student
		List<Student> students = new ArrayList<Student>();
		
		// take input from user and get student records from user
		System.out.println("How many student records you have?");
		n = Integer.valueOf(sc.nextLine());
		
		// use for loop to fill Student ArrayList
		for(int i = 0; i < n; i++) {
			
			String id, name, status;
			Boolean passed = false, fail = false;
			
			System.out.println("Enter id of "+(i+1)+" Student");
			id = sc.nextLine();
			System.out.println("Enter name of "+(i+1)+" Student");
			name = sc.nextLine();
			
			System.out.println("Is "+name+ " pass in exams(Yes/No)?: ");
			status = sc.nextLine();
			
			if(status.equals("Yes")) {
				passed = true;
			}
			
			if(status.equals("No")) {
				fail = false;
			}
			students.add(new Student(id, name, passed, fail));
		}
		// close Scanner class object
		sc.close();
		// serialize students into JSONArray
		String jsonArray = mapper.writeValueAsString(students);
		
		// deserialize JSON array into Java Array
		Student[] data = mapper.readValue(jsonArray, Student[].class);
		
		// use for each to iterate Student array
		for(Student std : data) {
			System.out.println("Student Id: "+std.getStdId());
			System.out.println("Student Name: "+std.getStdName());
			System.out.println("Is "+std.getStdName()+ "pass in exams(Yes/No)?: "+std.getPassed());
		}
		
	}
	
	
}

// create class Student
class Student {

	private String stdId;
	private String stdName;
	private Boolean passed;
	private Boolean fail;
	
	public Student() {
		this.stdId = null;
		this.stdName = null;
		this.passed = null;
		this.fail = null;
	}

	public Student(String stdId, String stdName, Boolean passed, Boolean fail) {
		this.stdId = stdId;
		this.stdName = stdName;
		this.passed = passed;
		this.fail = fail;
	}

	public String getStdId() {
		return stdId;
	}

	public String getStdName() {
		return stdName;
	}

	public Boolean getPassed() {
		return passed;
	}

	public Boolean getFail() {
		return fail;
	}

}

Output:

Deserialize to Collection/Array in Jackson

Deserialize JSON Array to Collection

Just like Java Array, we can also deserialize JSON Array to Java Collection by using the readValue() method of the ObjectMapper class.

Let's take an example to understand how we can deserialize JSON Array into java Collection by using Jackson:

DeserializeJSONArrayToJavaCollectionExample.java

//import required classes and package, if any
import java.util.ArrayList;
import java.util.List;
import java.util.Scanner;

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

// create class DeserializeJSONArrayToJavaArrayExample to deserialize JSONArray to Java Collection
public class DeserializeJSONArrayToJavaCollectionExample {
	
	//main() method start()
	public static void main(String args []) throws JsonProcessingException {
	
		int n;
		
		// create an instance of ObjectMapper class
		ObjectMapper mapper = new ObjectMapper();
		
		// create Scanner class object
		Scanner sc = new Scanner(System.in);
		
		// create an empty list of Student
		List<Student> students = new ArrayList<Student>();
		
		// take input from user and get student records from user
		System.out.println("How many student records you have?");
		n = Integer.valueOf(sc.nextLine());
		
		// use for loop to fill Student ArrayList
		for(int i = 0; i < n; i++) {
			
			String id, name, status;
			Boolean passed = false, fail = false;
			
			System.out.println("Enter id of "+(i+1)+" Student");
			id = sc.nextLine();
			System.out.println("Enter name of "+(i+1)+" Student");
			name = sc.nextLine();
			
			System.out.println("Is "+name+ " pass in exams(Yes/No)?: ");
			status = sc.nextLine();
			
			if(status.equals("Yes")) {
				passed = true;
			}
			
			if(status.equals("No")) {
				fail = false;
			}
			
			students.add(new Student(id, name, passed, fail));
			
		}
		
		// close Scanner class object
		sc.close();
		
		// serialize students into JSONArray
		String jsonArray = mapper.writeValueAsString(students);
		
		// deserialize JSON array into Java Array
		@SuppressWarnings("unchecked")
		List<Student> data = mapper.readValue(jsonArray, List.class);
		
		// use for each to iterate Student array
		for(int i = 0; i < data.size(); i++) {
			System.out.println("JSONArray after deserialize "+(Object) data.get(i));
		}
		
	}
	
	
}

//create class Student
class Student {

	private String stdId;
	private String stdName;
	private Boolean passed;
	private Boolean fail;
	
	public Student() {
		this.stdId = null;
		this.stdName = null;
		this.passed = null;
		this.fail = null;
	}

	public Student(String stdId, String stdName, Boolean passed, Boolean fail) {
		this.stdId = stdId;
		this.stdName = stdName;
		this.passed = passed;
		this.fail = fail;
	}

	public String getStdId() {
		return stdId;
	}

	public String getStdName() {
		return stdName;
	}

	public Boolean getPassed() {
		return passed;
	}

	public Boolean getFail() {
		return fail;
	}

}

Output: