Compare JSON Objects with Jackson

Jackson is one of the most used libraries for comparing JSON objects. Many times, we need to compare two JSON objects to find whether both are the same or different from each other.

In order to use Jakcson for comparing JSON objects, we add the following dependency in our POM.xml file:

<dependency>
    	<groupId>com.fasterxml.jackson.core</groupId>
    	<artifactId>jackson-databind</artifactId>
    	<version>2.13.0</version>
</dependency>

By using ObjectMapper class, we can compare:

Two simple JSON Objects.
Two JSON Objects with a nested element.
Two JSON Objects containing a list element.

Let's first understand the comparison of a simple JSON object.

Suppose we have a JSON string which is defined as the jsonString1:

{
	"student":
    	{
        		"stdId": "121",
        		"stdName": "Nicholas",
        		"passed": true,
		"fail": false
    	}
}

And, we need to compare it with another JSON string which is defined as jsonString2:

{
	"student":
    	{
        		"stdId": "122",
        		"stdName": "Brittany",
        		"passed": false,
		"fail": true
    	}
}

Let's take an example to understand how we can compare two simple JSON object by using Jackson:

CompareJSONObjectsExample1.java

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

//create class CompareJSONObjectsExample1 to compare two JSON Object
public class CompareJSONObjectsExample1 {
	
	//main() method start()
	public static void main(String args []) throws JsonProcessingException {
	
		int n = 2;
		
		// create an instance of ObjectMapper class
		ObjectMapper mapper = new ObjectMapper();
		
		// create Scanner class object
		Scanner sc = new Scanner(System.in);
		
		// create two Student objects
		Student std1 = new Student();
		Student std2 = new Student();
		
		// 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;
			}
			
			Student std = new Student(id, name, passed, fail);
			
			if(i == 0) {
				std1 = std;
			}else {
				std2 = std;
			}
		}
		
		// close Scanner class object
		sc.close();
		
		// serialize std1 and std2 into JSON object
		String jsonString1 = mapper.writeValueAsString(std1);
		String jsonString2 = mapper.writeValueAsString(std2);
		
		// read jsonString1 and jsonString2 as JsonNode
		JsonNode node1 = mapper.readTree(jsonString1);
		JsonNode node2 = mapper.readTree(jsonString2);
		
		// compare JSON Objects by using equals method of JsonNode
		if(node1.equals(node2)) {
			System.out.println("Both JSON Objects are identical.");
		}else {
			System.out.println("Both JSON Objects are not identical.");
		}
		
	}
	
	
}

//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:

We use the same techniques for comparing the JSON Objects having nested elements or a list of elements.

Compare JSON Objects with Custom Comparator

The JsonNode.equals() method works fine for most of the cases in comparing two objects. However, Jackson provides one more variant of the equals() method, i.e., JsonNode.equals(comparator, JsonNode) for configuring the custom Java Comparator object.

So, we can also use this variant of the equals() method for comparing two JSON objects. Let's first create a custom comparator, and later on, we will use it for comparing two JSON objects in an example.

Note: Standard equals() method considers values 121 and 121.0 as different.

NameNodeComparator.java

//import required classes and package
import java.util.Comparator;
import com.fasterxml.jackson.databind.JsonNode;
import com.fasterxml.jackson.databind.node.TextNode;

//create class IdNodeComparator to construct custom comparator
public class NameNodeComparator implements Comparator<JsonNode> 
{
	// override compare() method of Comparator class
	@Override
	public int compare(JsonNode node1, JsonNode node2)
	{
		// compare node1 and node2 by using equals() method
		if (node1.equals(node2)){
			return 0;
		}
     
		// check whether node1 and node2 is of type TextNode 
		if ((node1 instanceof TextNode) && (node2 instanceof TextNode)){
         
			// get JsonNode value as String
			String value1 = ((TextNode) node1).asText();
			String value2 = ((TextNode) node2).asText(); 
         
			// use compareTo() method to compare values
			if (value1.equalsIgnoreCase(value2)) {
				return 0;
			}
		}
		return 1;
	}
}

CompareJSONObjectsExample2.java

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

//create class CompareJSONObjectsExample1 to compare two JSON Object using custom comparator
public class CompareJSONObjectsExample2 {
	
	//main() method start()
	public static void main(String args []) throws JsonProcessingException {
	
		int n = 2;
		
		// create an instance of ObjectMapper class
		ObjectMapper mapper = new ObjectMapper();
		
		// create Scanner class object
		Scanner sc = new Scanner(System.in);
		
		// create two Student objects
		Student std1 = new Student();
		Student std2 = new Student();
		
		// 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;
			}
			
			Student std = new Student(id, name, passed, fail);
			
			if(i == 0) {
				std1 = std;
			}else {
				std2 = std;
			}
		}
		
		// close Scanner class object
		sc.close();
		
		// serialize std1 and std2 into JSON object
		String jsonString1 = mapper.writeValueAsString(std1);
		String jsonString2 = mapper.writeValueAsString(std2);
		
		// read jsonString1 and jsonString2 as JsonNode
		JsonNode node1 = mapper.readTree(jsonString1);
		JsonNode node2 = mapper.readTree(jsonString2);
		
		// create an instance of a custom comparator
		NameNodeComparator cmp = new NameNodeComparator();
		
		// compare JSON Objects by using custom comparator
		if(node1.equals(cmp, node2)) {
			System.out.println("Both JSON Objects are identical.");
		}else {
			System.out.println("Both JSON Objects are not identical.");
		}
		
	}
	
	
}

//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: