We have already learnt to create JSON Object using Jackson API
If you download and add jackson-databind jar to build path, do not forget to download other two transitive dependencies as well.
Class ObjectMapper
This is the most powerful class provided by Jackson API and maximum time we will use this class. As of now just know that ObjectMapper provides functionalities for reading and writing JSON. We will learn more about it as we proceed further.
We will use Class ObjectMapper to create a JSON Array or ArrayNode.
Let’s start with our familiar JSON Array payload which we will create using ObjectMapper.
[
{
"firstname":"Jim",
"lastname":"Brown",
"totalprice":111,
"depositpaid":true,
"additionalneeds":"Breakfast",
"bookingdates":{
"checkin":"2021-07-01",
"checkout":"2021-07-01"
}
},
{
"firstname" : "Amod",
"lastname" : "Mahajan",
"totalprice" : 222,
"depositpaid" : true,
"additionalneeds" : "Breakfast",
"bookingdates" : {
"checkin" : "2022-07-01",
"checkout" : "2022-07-01"
}
}
]
Above JSON payload is a JSON array which holds two JSON Objects. Out approach will be :-
- Create an empty JSON Array.
- Create first JSON Object
- Create second JSON Object
- Add created JSON Objects to JSON Array
Create an empty JSON Array
To create a JSON Object we used createObjectNode() method of ObjectMapper class. Similarly to create JSON Array we use createArrayNode() method of ObjectMapper class. createArrayNode() will return reference of ArrayNode class.
Note :- Return type of createArrayNode() or createObjectNode() is co-variant. We will see this concept later.
ObjectMapper objectMapper = new ObjectMapper();
// Create an array which will hold two JSON objects
ArrayNode parentArray = objectMapper.createArrayNode();
Create first JSON Object
We already know how to create JSON object using Jackson API.
// Creating Node that maps to JSON Object structures in JSON content
ObjectNode firstBookingDetails = objectMapper.createObjectNode();
// It is similar to map put method. put method is overloaded to accept different types of data
// String as field value
firstBookingDetails.put("firstname", "Jim");
firstBookingDetails.put("lastname", "Brown");
// integer as field value
firstBookingDetails.put("totalprice", 111);
// boolean as field value
firstBookingDetails.put("depositpaid", true);
firstBookingDetails.put("additionalneeds", "Breakfast");
// Since requirement is to create a nested JSON Object
ObjectNode firstBookingDateDetails = objectMapper.createObjectNode();
firstBookingDateDetails.put("checkin", "2021-07-01");
firstBookingDateDetails.put("checkout", "2021-07-01");
// Since 2.4 , put(String fieldName, JsonNode value) is deprecated. So use either set(String fieldName, JsonNode value) or replace(String fieldName, JsonNode value)
firstBookingDetails.set("bookingdates", firstBookingDateDetails);
Create second JSON Object
// Creating Node that maps to JSON Object structures in JSON content
ObjectNode secondBookingDetails = objectMapper.createObjectNode();
// It is similar to map put method. put method is overloaded to accept different types of data
// String as field value
secondBookingDetails.put("firstname", "Amod");
secondBookingDetails.put("lastname", "Mahajan");
// integer as field value
secondBookingDetails.put("totalprice", 222);
// boolean as field value
secondBookingDetails.put("depositpaid", true);
secondBookingDetails.put("additionalneeds", "Breakfast");
// Since requirement is to create a nested JSON Object
ObjectNode secondBookingDateDetails = objectMapper.createObjectNode();
secondBookingDateDetails.put("checkin", "2022-07-01");
secondBookingDateDetails.put("checkout", "2022-07-01");
// Since 2.4 , put(String fieldName, JsonNode value) is deprecated. So use either set(String fieldName, JsonNode value) or replace(String fieldName, JsonNode value)
secondBookingDetails.set("bookingdates", secondBookingDateDetails);
Add created JSON Objects to JSON Array
Class ArrayNode provides a method add() which can add one JSON Object to array at a time.
parentArray.add(firstBookingDetails);
parentArray.add(secondBookingDetails);
To add multiple Object Nodes to array at a time we can use addAll() method which accepts a Collection<? extends JsonNode> . We can create a List (because List extends Collection)of all JSON Objects and add.
parentArray.addAll(Arrays.asList(firstBookingDetails,secondBookingDetails));
Note:- If you try to add duplicate Object Nodes, it will be added to array.
To print created JSON array as string with proper format
String jsonArrayAsString = objectMapper.writerWithDefaultPrettyPrinter().writeValueAsString(parentArray);
System.out.println("Created Json Array is : ");
System.out.println(jsonArrayAsString);
That’s all. We have created a JSON Array successfully using Jackson API.
Let’s learn some retrieving and manipulation methods.
Retrieving JSON Object from JSON array using index
Since JSON Array is iterable, we can retrieve a JSON object using its index.
// To get json array element using index
JsonNode firstElement = parentArray.get(0);
System.out.println(objectMapper.writerWithDefaultPrettyPrinter().writeValueAsString(firstElement));
Get size of JSON Array
size() method can be used to get size of JSON Array.
| int sizeOfArray = parentArray.size(); System.out.println(“Size of array is “+sizeOfArray); |
Iterate JSON Array
iterator() method can be used to iterate through a JSON Array.
// To iterate JSON Array
Iterator<JsonNode> iteraor = parentArray.iterator();
System.out.println("Prining Json Node using iterator : ");
while(iteraor.hasNext())
{
JsonNode currentJsonNode = iteraor.next();
System.out.println(objectMapper.writerWithDefaultPrettyPrinter().writeValueAsString(currentJsonNode));
}
Remove a JSON Object from JSON Array
We can remove a JSON object from JSON Array using its index.
// To remove an element from array
parentArray.remove(0);
System.out.println("After removing first element from array : "+ objectMapper.writerWithDefaultPrettyPrinter().writeValueAsString(parentArray));
Empty JSON Array
// To empty JSON Array
parentArray.removeAll();
System.out.println("After removing all elements from array : "+ objectMapper.writerWithDefaultPrettyPrinter().writeValueAsString(parentArray));
| // To empty JSON ArrayparentArray.removeAll();System.out.println(“After removing all elements from array : “+ objectMapper.writerWithDefaultPrettyPrinter().writeValueAsString(parentArray)); |
Complete Program
package JacksonAPIUsage;
import java.util.Arrays;
import java.util.Iterator;
import com.fasterxml.jackson.core.JsonProcessingException;
import com.fasterxml.jackson.databind.JsonNode;
import com.fasterxml.jackson.databind.ObjectMapper;
import com.fasterxml.jackson.databind.node.ArrayNode;
import com.fasterxml.jackson.databind.node.ObjectNode;
/*
* [
{
"firstname":"Jim",
"lastname":"Brown",
"totalprice":111,
"depositpaid":true,
"additionalneeds":"Breakfast",
"bookingdates":{
"checkin":"2021-07-01",
"checkout":"2021-07-01"
}
},
{
"firstname":"Amod",
"lastname":"Mahajan",
"totalprice":222,
"depositpaid":true,
"additionalneeds":"Lunch",
"bookingdates":{
"checkin":"2022-07-01",
"checkout":"2022-07-01"
}
}
]
*
*/
public class CreateJsonArrayUsingJacksonAPI {
public static void main(String[] args) throws JsonProcessingException {
ObjectMapper objectMapper = new ObjectMapper();
// Create an array which will hold two JSON objects
ArrayNode parentArray = objectMapper.createArrayNode();
// Creating Node that maps to JSON Object structures in JSON content
ObjectNode firstBookingDetails = objectMapper.createObjectNode();
// It is similar to map put method. put method is overloaded to accept different types of data
// String as field value
firstBookingDetails.put("firstname", "Jim");
firstBookingDetails.put("lastname", "Brown");
// integer as field value
firstBookingDetails.put("totalprice", 111);
// boolean as field value
firstBookingDetails.put("depositpaid", true);
firstBookingDetails.put("additionalneeds", "Breakfast");
// Since requirement is to create a nested JSON Object
ObjectNode firstBookingDateDetails = objectMapper.createObjectNode();
firstBookingDateDetails.put("checkin", "2021-07-01");
firstBookingDateDetails.put("checkout", "2021-07-01");
// Since 2.4 , put(String fieldName, JsonNode value) is deprecated. So use either set(String fieldName, JsonNode value) or replace(String fieldName, JsonNode value)
firstBookingDetails.set("bookingdates", firstBookingDateDetails);
// Creating Node that maps to JSON Object structures in JSON content
ObjectNode secondBookingDetails = objectMapper.createObjectNode();
// It is similar to map put method. put method is overloaded to accept different types of data
// String as field value
secondBookingDetails.put("firstname", "Amod");
secondBookingDetails.put("lastname", "Mahajan");
// integer as field value
secondBookingDetails.put("totalprice", 222);
// boolean as field value
secondBookingDetails.put("depositpaid", true);
secondBookingDetails.put("additionalneeds", "Breakfast");
// Since requirement is to create a nested JSON Object
ObjectNode secondBookingDateDetails = objectMapper.createObjectNode();
secondBookingDateDetails.put("checkin", "2022-07-01");
secondBookingDateDetails.put("checkout", "2022-07-01");
// Since 2.4 , put(String fieldName, JsonNode value) is deprecated. So use either set(String fieldName, JsonNode value) or replace(String fieldName, JsonNode value)
secondBookingDetails.set("bookingdates", secondBookingDateDetails);
parentArray.add(firstBookingDetails);
parentArray.add(secondBookingDetails);
// OR
parentArray.addAll(Arrays.asList(firstBookingDetails,secondBookingDetails));
String jsonArrayAsString = objectMapper.writerWithDefaultPrettyPrinter().writeValueAsString(parentArray);
System.out.println("Created Json Array is : ");
System.out.println(jsonArrayAsString);
System.out.println("=======================================================================================");
// To get json array element using index
JsonNode firstElement = parentArray.get(0);
System.out.println(objectMapper.writerWithDefaultPrettyPrinter().writeValueAsString(firstElement));
System.out.println("=======================================================================================");
// To get size of JSON array
int sizeOfArray = parentArray.size();
System.out.println("Size of array is "+sizeOfArray);
System.out.println("=======================================================================================");
// To iterate JSON Array
Iterator<JsonNode> iteraor = parentArray.iterator();
System.out.println("Prining Json Node using iterator : ");
while(iteraor.hasNext())
{
JsonNode currentJsonNode = iteraor.next();
System.out.println(objectMapper.writerWithDefaultPrettyPrinter().writeValueAsString(currentJsonNode));
}
System.out.println("=======================================================================================");
// To remove an element from array
parentArray.remove(0);
System.out.println("After removing first element from array : "+ objectMapper.writerWithDefaultPrettyPrinter().writeValueAsString(parentArray));
System.out.println("=======================================================================================");
// To empty JSON Array
parentArray.removeAll();
System.out.println("After removing all elements from array : "+ objectMapper.writerWithDefaultPrettyPrinter().writeValueAsString(parentArray));
}
}
Output
Created Json Array is :
[ {
"firstname" : "Jim",
"lastname" : "Brown",
"totalprice" : 111,
"depositpaid" : true,
"additionalneeds" : "Breakfast",
"bookingdates" : {
"checkin" : "2021-07-01",
"checkout" : "2021-07-01"
}
}, {
"firstname" : "Amod",
"lastname" : "Mahajan",
"totalprice" : 222,
"depositpaid" : true,
"additionalneeds" : "Breakfast",
"bookingdates" : {
"checkin" : "2022-07-01",
"checkout" : "2022-07-01"
}
}, {
"firstname" : "Jim",
"lastname" : "Brown",
"totalprice" : 111,
"depositpaid" : true,
"additionalneeds" : "Breakfast",
"bookingdates" : {
"checkin" : "2021-07-01",
"checkout" : "2021-07-01"
}
}, {
"firstname" : "Amod",
"lastname" : "Mahajan",
"totalprice" : 222,
"depositpaid" : true,
"additionalneeds" : "Breakfast",
"bookingdates" : {
"checkin" : "2022-07-01",
"checkout" : "2022-07-01"
}
} ]
=======================================================================================
{
"firstname" : "Jim",
"lastname" : "Brown",
"totalprice" : 111,
"depositpaid" : true,
"additionalneeds" : "Breakfast",
"bookingdates" : {
"checkin" : "2021-07-01",
"checkout" : "2021-07-01"
}
}
=======================================================================================
Size of array is 4
=======================================================================================
Prining Json Node using iterator :
{
"firstname" : "Jim",
"lastname" : "Brown",
"totalprice" : 111,
"depositpaid" : true,
"additionalneeds" : "Breakfast",
"bookingdates" : {
"checkin" : "2021-07-01",
"checkout" : "2021-07-01"
}
}
{
"firstname" : "Amod",
"lastname" : "Mahajan",
"totalprice" : 222,
"depositpaid" : true,
"additionalneeds" : "Breakfast",
"bookingdates" : {
"checkin" : "2022-07-01",
"checkout" : "2022-07-01"
}
}
{
"firstname" : "Jim",
"lastname" : "Brown",
"totalprice" : 111,
"depositpaid" : true,
"additionalneeds" : "Breakfast",
"bookingdates" : {
"checkin" : "2021-07-01",
"checkout" : "2021-07-01"
}
}
{
"firstname" : "Amod",
"lastname" : "Mahajan",
"totalprice" : 222,
"depositpaid" : true,
"additionalneeds" : "Breakfast",
"bookingdates" : {
"checkin" : "2022-07-01",
"checkout" : "2022-07-01"
}
}
=======================================================================================
After removing first element from array : [ {
"firstname" : "Amod",
"lastname" : "Mahajan",
"totalprice" : 222,
"depositpaid" : true,
"additionalneeds" : "Breakfast",
"bookingdates" : {
"checkin" : "2022-07-01",
"checkout" : "2022-07-01"
}
}, {
"firstname" : "Jim",
"lastname" : "Brown",
"totalprice" : 111,
"depositpaid" : true,
"additionalneeds" : "Breakfast",
"bookingdates" : {
"checkin" : "2021-07-01",
"checkout" : "2021-07-01"
}
}, {
"firstname" : "Amod",
"lastname" : "Mahajan",
"totalprice" : 222,
"depositpaid" : true,
"additionalneeds" : "Breakfast",
"bookingdates" : {
"checkin" : "2022-07-01",
"checkout" : "2022-07-01"
}
} ]
=======================================================================================
After removing all elements from array : [ ]