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Need to extract data from a JSON string in Java? With Jackson’s JsonNode and ObjectMapper, it’s a breeze. Here's how to parse simple, nested, and array-based JSON using JsonNode.

✅ 1. Add Jackson Dependency

Add this to your pom.xml:

xml

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

📦 2. Parse Simple JSON String

java

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

public class JsonNodeExample {
    public static void main(String[] args) {
        String jsonString = "{\"name\":\"John\",\"age\":30,\"city\":\"New York\"}";

        try {
            ObjectMapper objectMapper = new ObjectMapper();
            JsonNode jsonNode = objectMapper.readTree(jsonString);

            String name = jsonNode.get("name").asText();
            int age = jsonNode.get("age").asInt();
            String city = jsonNode.get("city").asText();

            System.out.println("Name: " + name);
            System.out.println("Age: " + age);
            System.out.println("City: " + city);
        } catch (Exception e) {
            e.printStackTrace();
        }
    }
}

🌐 3. Handle Nested JSON

java

String nestedJson = "{\"person\":{\"name\":\"John\",\"age\":30,\"address\":{\"city\":\"New York\",\"zip\":\"10001\"}}}";

ObjectMapper mapper = new ObjectMapper();
JsonNode rootNode = mapper.readTree(nestedJson);

JsonNode personNode = rootNode.get("person");
String name = personNode.get("name").asText();
int age = personNode.get("age").asInt();
String city = personNode.get("address").get("city").asText();
String zip = personNode.get("address").get("zip").asText();

🔁 4. Parse JSON Array and Get First Item

java

String jsonArray = "[{\"name\":\"John\",\"age\":30},{\"name\":\"Jane\",\"age\":25}]";

ObjectMapper mapper = new ObjectMapper();
JsonNode arrayNode = mapper.readTree(jsonArray);

if (arrayNode.isArray()) {
    Iterator<JsonNode> itr = arrayNode.iterator();

    if (itr.hasNext()) {
        JsonNode firstItem = itr.next();
        String name = firstItem.get("name").asText();
        int age = firstItem.get("age").asInt();

        System.out.println("First item - Name: " + name + ", Age: " + age);
    }
}

📝 Summary

TaskHowParse JSON stringobjectMapper.readTree(jsonString)Access simple fieldjsonNode.get("key").asText()/asInt()Access nested fieldjsonNode.get("parent").get("child")Handle arrayif (jsonNode.isArray()) + iterate using .iterator()Get first item from arrayiterator.hasNext() + iterator.next()