Jackson Tree Model examples

Jackson’s Tree Model provides a flexible way to work with JSON data compared to the data-binding method. The Tree Model works well when the JSON data or JSON’s schema is unknown until runtime or the JSON structure does not map properly to Java classes.

This article shows how to use Jackson’s Tree Model JsonNode and ObjectNode to parse, access, add, modify, remove, and generate JSON.

Table of contents:

• 1. Download Jackson
• 2. Accessing the JSON using JsonNode
• 2. Accessing the JSON Array using JsonNode
• 3. CRUD JSON using the ObjectNode
• 4. Download Source Code
• 5. References

P.S Tested with Jackson 2.17.0

1. Download Jackson

Declares jackson-databind at pom.xml.

  <dependency>
    <groupId>com.fasterxml.jackson.core</groupId>
    <artifactId>jackson-databind</artifactId>
    <version>2.17.0</version>
  </dependency>

2. Accessing the JSON using JsonNode

The following example shows how to use Jackson TreeModel to traversing or accessing the JSON data.

Example JSON data.

{
  "id": 1,
  "name": {
    "first": "Yong",
    "last": "Mook Kim"
  },
  "contact": [
    {
      "type": "phone/home",
      "ref": "111-111-1234"
    },
    {
      "type": "phone/work",
      "ref": "222-222-2222"
    }
  ]
}

package com.mkyong.json.jackson.treemodel;

import com.fasterxml.jackson.databind.JsonNode;
import com.fasterxml.jackson.databind.ObjectMapper;

import java.io.IOException;

public class JacksonTreeModelExample1 {

    public static void main(String[] args) {

        String json = """
                {
                  "id": 1,
                  "name": {
                    "first": "Yong",
                    "last": "Mook Kim"
                  },
                  "contact": [
                    {
                      "type": "phone/home",
                      "ref": "111-111-1234"
                    },
                    {
                      "type": "phone/work",
                      "ref": "222-222-2222"
                    }
                  ]
                }
                """;
        try {

            ObjectMapper mapper = new ObjectMapper();

            // read from a json file
            //JsonNode root = mapper.readTree(new File("tree/user.json"));

            // read from a json string
            JsonNode root = mapper.readTree(json);

            // Get id
            long id = root.path("id").asLong();
            System.out.println("id : " + id);

            // Get Name
            JsonNode nameNode = root.path("name");
            if (!nameNode.isMissingNode()) {        // if "name" node exists?
                System.out.println("firstName : " + nameNode.path("first").asText());
                System.out.println("middleName : " + nameNode.path("middle").asText());
                System.out.println("lastName : " + nameNode.path("last").asText());
            }

            // Get Contact
            JsonNode contactNode = root.path("contact");
            if (contactNode.isArray()) {

                System.out.println("Is this node an Array? " + contactNode.isArray());

                for (JsonNode node : contactNode) {
                    String type = node.path("type").asText();
                    String ref = node.path("ref").asText();
                    System.out.println("type : " + type);
                    System.out.println("ref : " + ref);

                }
            }

        } catch (IOException e) {
            throw new RuntimeException(e);
        }
    }
}

Output

id : 1
firstName : Yong
middleName : 
lastName : Mook Kim
Is this node an Array? true
type : phone/home
ref : 111-111-1234
type : phone/work
ref : 222-222-2222

2. Accessing the JSON Array using JsonNode

The following example shows how Jackson TreeModel can traverse or access the JSON array.

Example of JSON array

[
  {
    "id": 1,
    "name": {
      "first": "Yong",
      "last": "Mook Kim"
    },
    "contact": [
      {
        "type": "phone/home",
        "ref": "111-111-1234"
      },
      {
        "type": "phone/work",
        "ref": "222-222-2222"
      }
    ]
  },
  {
    "id": 2,
    "name": {
      "first": "Yong",
      "last": "Zi Lap"
    },
    "contact": [
      {
        "type": "phone/home",
        "ref": "333-333-1234"
      },
      {
        "type": "phone/work",
        "ref": "444-444-4444"
      }
    ]
  }
]

The concept is the same: loop the JSON array:

	JsonNode rootArray = mapper.readTree(new File("c:\\projects\\user2.json"));

	for (JsonNode root : rootArray) {
		// get node like the above example 1
	}

package com.mkyong.json.jackson.treemodel;

import com.fasterxml.jackson.databind.JsonNode;
import com.fasterxml.jackson.databind.ObjectMapper;

import java.io.File;
import java.io.IOException;

public class JacksonTreeModelExample2 {

    public static void main(String[] args) {

        try {

            ObjectMapper mapper = new ObjectMapper();

            JsonNode rootArray = mapper.readTree(new File("tree/user2.json"));

            for (JsonNode root : rootArray) {

                // Get id
                long id = root.path("id").asLong();
                System.out.println("id : " + id);

                // Get Name
                JsonNode nameNode = root.path("name");
                if (!nameNode.isMissingNode()) {        // if "name" node exists?
                    System.out.println("firstName : " + nameNode.path("first").asText());
                    System.out.println("middleName : " + nameNode.path("middle").asText());
                    System.out.println("lastName : " + nameNode.path("last").asText());
                }

                // Get Contact
                JsonNode contactNode = root.path("contact");
                if (contactNode.isArray()) {

                    System.out.println("Is this node an Array? " + contactNode.isArray());

                    for (JsonNode node : contactNode) {
                        String type = node.path("type").asText();
                        String ref = node.path("ref").asText();
                        System.out.println("type : " + type);
                        System.out.println("ref : " + ref);

                    }
                }

            }

        } catch (IOException e) {
            throw new RuntimeException(e);
        }

    }

}

Output

id : 1
firstName : Yong
middleName : 
lastName : Mook Kim
Is this node an Array? true
type : phone/home
ref : 111-111-1234
type : phone/work
ref : 222-222-2222
id : 2
firstName : Yong
middleName : 
lastName : Zi Lap
Is this node an Array? true
type : phone/home
ref : 333-333-1234
type : phone/work
ref : 444-444-4444

3. CRUD JSON using the ObjectNode

The following example shows how to create, update, and remove new JSON nodes.

Example of JSON data.

{
  "id" : 1,
  "name" : {
    "first" : "Yong",
    "last" : "Mook Kim"
  },
  "contact" : [ {
    "type" : "phone/home",
    "ref" : "111-111-1234"
  }, {
    "type" : "phone/work",
    "ref" : "222-222-2222"
  } ]
}

We will modify the above JSON data into the following JSON data.

{
  "id" : 1000,
  "name" : {
    "first" : "Yong",
    "middle" : "M",
    "nickname" : "mkyong"
  },
  "contact" : [ {
    "type" : "phone/home",
    "ref" : "111-111-1234"
  }, {
    "type" : "phone/work",
    "ref" : "222-222-2222"
  }, {
    "type" : "email",
    "ref" : "[email protected]"
  } ],
  "position" : {
    "name" : "Developer",
    "years" : 10
  },
  "games" : [ {
    "name" : "Fall Out 4",
    "price" : 49.9
  }, {
    "name" : "Dark Soul 3",
    "price" : 59.9
  } ]
}

Read the comments for self-explanatory.

package com.mkyong.json.jackson.treemodel;

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;

import java.io.File;
import java.io.IOException;

public class JacksonTreeModelExample3 {

    public static void main(String[] args) {

        try {

            ObjectMapper mapper = new ObjectMapper();

            JsonNode root = mapper.readTree(new File("tree/user.json"));

            // pretty print
            String resultOriginal = mapper
                    .writerWithDefaultPrettyPrinter()
                    .writeValueAsString(root);
            System.out.println("Before Update " + resultOriginal);

            // modifying data
            // 1. Update id to 1000
            ((ObjectNode) root).put("id", 1000L);

            // 2. If middle name is empty , update to M
            ObjectNode nameNode = (ObjectNode) root.path("name");
            if (nameNode.path("middle").asText().isEmpty()) {
                nameNode.put("middle", "M");
            }

            // Adding new data
            // 3. Create a new field in nameNode
            nameNode.put("nickname", "mkyong");

            // remove data
            // 4. Remove last field in nameNode
            nameNode.remove("last");

            // 5. Create a new ObjectNode and add to root
            ObjectNode positionNode = mapper.createObjectNode();
            positionNode.put("name", "Developer");
            positionNode.put("years", 10);
            ((ObjectNode) root).set("position", positionNode);

            // 6. Create a new ArrayNode and add to root
            ArrayNode gamesNode = mapper.createArrayNode();

            ObjectNode game1 = mapper.createObjectNode().objectNode();
            game1.put("name", "Fall Out 4");
            game1.put("price", 49.9);

            ObjectNode game2 = mapper.createObjectNode().objectNode();
            game2.put("name", "Dark Soul 3");
            game2.put("price", 59.9);

            gamesNode.add(game1);
            gamesNode.add(game2);
            ((ObjectNode) root).set("games", gamesNode);

            // 7. Append a new Node to ArrayNode
            ObjectNode email = mapper.createObjectNode();
            email.put("type", "email");
            email.put("ref", "[email protected]");

            JsonNode contactNode = root.path("contact");
            ((ArrayNode) contactNode).add(email);

            String resultUpdate = mapper.writerWithDefaultPrettyPrinter().writeValueAsString(root);

            System.out.println("After Update " + resultUpdate);

        } catch (IOException e) {
            throw new RuntimeException(e);
        }
    }

}

Output

Before Update {
  "id" : 1,
  "name" : {
    "first" : "Yong",
    "last" : "Mook Kim"
  },
  "contact" : [ {
    "type" : "phone/home",
    "ref" : "111-111-1234"
  }, {
    "type" : "phone/work",
    "ref" : "222-222-2222"
  } ]
}
After Update {
  "id" : 1000,
  "name" : {
    "first" : "Yong",
    "middle" : "M",
    "nickname" : "mkyong"
  },
  "contact" : [ {
    "type" : "phone/home",
    "ref" : "111-111-1234"
  }, {
    "type" : "phone/work",
    "ref" : "222-222-2222"
  }, {
    "type" : "email",
    "ref" : "[email protected]"
  } ],
  "position" : {
    "name" : "Developer",
    "years" : 10
  },
  "games" : [ {
    "name" : "Fall Out 4",
    "price" : 49.9
  }, {
    "name" : "Dark Soul 3",
    "price" : 59.9
  } ]
}

4. Download Source Code

5. References

• Jackson Github
• Stackoverflow – Adding property to JSON using Jackson
• Parse JSON string with Jackson
• Parse JSON Array with Jackson
• Convert Java Objects to JSON with Jackson
• Jackson and Lombok examples
• Jackson Streaming API examples