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Discovering ObjectMapper and JsonNode

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Sahil Sudan
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Table of contents

1. ObjectMapper

The ObjectMapper class is the core of Jackson's JSON processing. It provides functionality to:

  • Serialize Java objects to JSON (convert Java objects into JSON strings).

  • Deserialize JSON to Java objects (convert JSON strings into Java objects).

  • Work with tree structures, like JsonNode.

Common Use Cases:

  1. Converting a JSON string into a Java object:

     javaCopy codeObjectMapper objectMapper = new ObjectMapper();
 String json = "{\"name\": \"John\", \"age\": 30}";
 Person person = objectMapper.readValue(json, Person.class); // Deserialize JSON to a Person object

  2. Converting a Java object into a JSON string:

     javaCopy codePerson person = new Person("John", 30);
 String json = objectMapper.writeValueAsString(person); // Serialize Person object to JSON
 System.out.println(json);

  3. Parsing JSON into a tree structure (JsonNode):

     javaCopy codeString json = "{\"name\": \"John\", \"age\": 30}";
 JsonNode rootNode = objectMapper.readTree(json); // Parse JSON into a JsonNode

2. JsonNode

The JsonNode class represents a JSON object or value as a tree structure. It is part of Jackson's Tree Model and allows you to navigate and manipulate JSON data without binding it to a specific Java class.

Common Use Cases:

  1. Accessing JSON fields:

     javaCopy codeString json = "{\"name\": \"John\", \"age\": 30}";
 JsonNode rootNode = objectMapper.readTree(json);

 String name = rootNode.get("name").asText(); // Get "name" field as a string
 int age = rootNode.get("age").asInt(); // Get "age" field as an integer

 System.out.println("Name: " + name);
 System.out.println("Age: " + age);

  2. Iterating over JSON fields:

     javaCopy codeJsonNode rootNode = objectMapper.readTree("{\"name\": \"John\", \"age\": 30}");
 Iterator<Map.Entry<String, JsonNode>> fields = rootNode.fields();

 while (fields.hasNext()) {
     Map.Entry<String, JsonNode> field = fields.next();
     System.out.println(field.getKey() + ": " + field.getValue().asText());
 }

  3. Checking the type of a JSON field:

     javaCopy codeJsonNode rootNode = objectMapper.readTree("{\"name\": \"John\", \"isActive\": true}");
 boolean isActive = rootNode.get("isActive").isBoolean(); // Check if the field is a boolean

In Summary:

  • ObjectMapper: The primary utility for JSON serialization, deserialization, and parsing.

  • JsonNode: A lightweight, tree-like representation of JSON data that allows easy traversal and manipulation without mapping to Java objects.

These classes are essential for handling JSON in Java applications, especially in scenarios where dynamic or complex JSON structures are involved.

JavaBackend Development