Jackson – Tree Model examples

In Jackson, we can use Tree Model to represent the JSON structure, and perform the CRUD operations via JsonNode, similar to the XML DOM tree. This Jackson Tree Model is useful, especially in cases where a JSON structure does not map nicely to Java classes.

pom.xml

	<dependency>
		<groupId>com.fasterxml.jackson.core</groupId>
		<artifactId>jackson-databind</artifactId>
		<version>2.9.8</version>
	</dependency>

P.S Tested with Jackson 2.9.8

1. Traversing JSON

1.1 Jackson TreeModel example to traversing below JSON file:

C:\\projects\\user.json

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

1.2 Process JsonNode one by one.

JacksonTreeModelExample1.java

package com.favtuts.json;

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

import com.fasterxml.jackson.core.JsonGenerationException;
import com.fasterxml.jackson.databind.JsonMappingException;
import com.fasterxml.jackson.databind.JsonNode;
import com.fasterxml.jackson.databind.ObjectMapper;

public class JacksonTreeModelExamples {

    private static final ObjectMapper mapper = new ObjectMapper();

    public static void main(String[] args) {
        traverseJSONprocessJsonNodeOneByOne();
    }

    static void traverseJSONprocessJsonNodeOneByOne() {
        try {

            JsonNode root = mapper.readTree(new File("/home/tvt/workspace/favtuts/user.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 is exist
                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 (JsonGenerationException e) {
            e.printStackTrace();
        } catch (JsonMappingException e) {
            e.printStackTrace();
        } catch (IOException e) {
            e.printStackTrace();
        }
    }
}

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. Traversing JSON Array

2.1 JSON file, top level represents an Array.

c:\\projects\\user2.json

[
    {
        "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"
            }
        ]
    }
]

2.2 The concept is same, just 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
	}

JacksonTreeModelExample2.java

package com.favtuts.json;

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

import com.fasterxml.jackson.core.JsonGenerationException;
import com.fasterxml.jackson.databind.JsonMappingException;
import com.fasterxml.jackson.databind.JsonNode;
import com.fasterxml.jackson.databind.ObjectMapper;

public class JacksonTreeModelExamples {

    private static final ObjectMapper mapper = new ObjectMapper();

    public static void main(String[] args) {
        traverseJSONarrayProcessJsonNodeOneByOne();
    }

    static void traverseJSONarrayProcessJsonNodeOneByOne() {
        try {

            JsonNode rootArray = mapper.readTree(new File("/home/tvt/workspace/favtuts/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 is exist
                    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 (JsonGenerationException e) {
            e.printStackTrace();
        } catch (JsonMappingException e) {
            e.printStackTrace();
        } catch (IOException e) {
            e.printStackTrace();
        }
    }
}

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. Tree model CRUD example

3.1 This example, show you how to create, update and remove JSON nodes, to modify JSON node, we need to convert it to ObjectNode. Read the comments for self-explanatory.

JacksonTreeModelExample3.java

package com.favtuts.json;

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

import com.fasterxml.jackson.core.JsonGenerationException;
import com.fasterxml.jackson.databind.JsonMappingException;
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;

public class JacksonTreeModelExamples {

    private static final ObjectMapper mapper = new ObjectMapper();

    public static void main(String[] args) {
        treeModelCRUDexamples();
    }

    static void treeModelCRUDexamples() {
        try {

            JsonNode root = mapper.readTree(new File("/home/tvt/workspace/favtuts/user.json"));

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

            // 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 ("".equals(nameNode.path("middle").asText())) {
                nameNode.put("middle", "M");
            }

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

            // 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", "abc@tuts.heomi.net");

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

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

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

        } catch (JsonGenerationException e) {
            e.printStackTrace();
        } catch (JsonMappingException e) {
            e.printStackTrace();
        } catch (IOException e) {
            e.printStackTrace();
        }
    }
}

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" : "favtuts"
  },
  "contact" : [ {
    "type" : "phone/home",
    "ref" : "111-111-1234"
  }, {
    "type" : "phone/work",
    "ref" : "222-222-2222"
  }, {
    "type" : "email",
    "ref" : "abc@tuts.heomi.net"
  } ],
  "position" : {
    "name" : "Developer",
    "years" : 10
  },
  "games" : [ {
    "name" : "Fall Out 4",
    "price" : 49.9
  }, {
    "name" : "Dark Soul 3",
    "price" : 59.9
  } ]
}

Download Source Code

$ git clone https://github.com/favtuts/java-core-tutorials-examples

$ cd java-basic/json

References

• Json processing with Jackson: Method #3/3: Tree Traversal
• Jackson data-binding guide
• Jackson 2 – Convert Java Object to / from JSON
• Stackoverflow – Adding property to JSON using Jackson