Mastering Jackson JsonNode in Spring Boot 3: From Parsing to Modification

1. Introduction

When JSON structures are dynamic or unknown at compile time, traditional POJOs cannot be defined ahead of time. Using Map<String, Object> loses type information and makes nested access cumbersome. Jackson's JsonNode tree model preserves the full JSON hierarchy, allows type‑safe traversal, and enables selective deserialization of sub‑trees.

2. Sample JSON and POJOs

Example JSON representing a user with contact information and a list of orders:

static String json = """
{
  "user": {
    "name": "pack_xg",
    "age": 33,
    "contact": {
      "email": "[email protected]",
      "phones": ["13800138000", "010-12345678"]
    }
  },
  "orders": [
    {
      "orderId": "D20260101001",
      "items": [
        {"name": "无线蓝牙耳机", "price": 299.99, "quantity": 1},
        {"name": "手机保护壳", "price": 39.5, "quantity": 2}
      ],
      "totalAmount": 379.0,
      "shipped": true
    }
  ]
}
""";

Corresponding Java classes:

public class User {
    private String name;
    private int age;
    private Contact contact;
    private List<Order> orders;
}

public class Contact {
    private String email;
    private List<String> phones;
}

public class Order {
    private String orderId;
    private List<Item> items;
    private double totalAmount;
    private boolean shipped;
}

public class Item {
    private String name;
    private double price;
    private int quantity;
}

3. Basic JsonNode Operations

3.1 Parse JSON to an ObjectNode

ObjectMapper mapper = new ObjectMapper();
ObjectNode rootNode = mapper.readValue(json, ObjectNode.class);

3.2 Access fields

JsonNode userNode = rootNode.get("user");
System.out.println(userNode); // {"name":"pack_xg","age":33,"contact":{...}}

String name = userNode.get("name").asText();
int age = userNode.get("age").asInt();
System.out.println(name); // pack_xg
System.out.println(age);  // 33

JsonNode phones = userNode.get("contact").get("phones");
if (phones.isArray()) {
    phones.forEach(p -> System.out.println(p.asText()));
}
// 13800138000
// 010-12345678

3.3 Convert a JsonNode to a POJO

User user = mapper.treeToValue(userNode, User.class);
System.out.println(user);
// User[name=pack_xg, age=33, contact=Contact[[email protected], phones=[13800138000, 010-12345678]], orders=...]

3.4 Find values

JsonNode emailNode = userNode.findValue("email");
System.out.println(emailNode.asText()); // [email protected]

JsonNode missing = userNode.findPath("nonexistent");
System.out.println(missing instanceof MissingNode); // true

3.5 Iterate all properties of a node

userNode.fields().forEachRemaining(entry -> {
    System.out.printf("%s : %s%n", entry.getKey(), entry.getValue());
});
// name : "pack_xg"
// age : 33
// contact : {"email":"...","phones":[...]}

4. Path‑Based Operations

JsonNode root = mapper.readTree(json);
JsonNode nameNode = root.at("/user/name");
System.out.println(nameNode.asText()); // pack_xg

JsonNode secondPhone = root.at("/user/contact/phones/1");
System.out.println(secondPhone.asText()); // 010-12345678

JsonNode price = root.at("/orders/0/items/0/price");
System.out.println(price.asDouble()); // 299.99

List<Item> items = mapper.treeToValue(root.at("/orders/0/items"), new TypeReference<List<Item>>() {});
System.out.println(items);
// [Item[name=无线蓝牙耳机, price=299.99, quantity=1], Item[name=手机保护壳, price=39.5, quantity=2]]

5. Modifying JSON

5.1 Update a simple field

ObjectNode rootNode = mapper.readValue(json, ObjectNode.class);
ObjectNode userObj = (ObjectNode) rootNode.get("user");
userObj.put("age", 30);
System.out.println(userObj);
// {"name":"pack_xg","age":30,"contact":{...}}

5.2 Replace a nested object with a POJO

Contact newContact = new Contact("[email protected]", List.of("111111", "222222"));
userObj.putPOJO("contact", newContact);
System.out.println(userObj);
// {"name":"pack_xg","age":30,"contact":{"email":"[email protected]","phones":["111111","222222"]}}

5.3 Delete a node

JsonNode removed = userObj.remove("age");
System.out.println("Removed value: " + removed.asInt()); // Removed value: 30
System.out.println(userObj);
// {"name":"pack_xg","contact":{...}}

5.4 Remove all children of a node

userObj.removeAll();
System.out.println(userObj); // {}

This guide demonstrates how to parse, query, convert, and mutate JSON using Jackson's JsonNode API in a Spring Boot 3.5.0 project.