Java Jackson XML Custom Deserializer

1. Overview

In data processing tasks, sometimes the default deserialization behavior might not suffice, especially when dealing with complex or non-standard XML structures. Jackson provides a mechanism to define custom deserializers, giving developers the power to dictate exactly how XML data should be converted into Java objects. This guide focuses on creating a custom deserializer for user data in an XML format.

@JsonDeserialize: This annotation is used on the target class or field to specify the custom deserializer that should be used.

Check out all the Java Jackson JSON tutorials and examples: 50+ Java Jackson JSON Tutorials with Examples

2. Development Steps

1. Set up a new Maven project.

2. Add the necessary Jackson XML dependencies.

3. Define the User Java class and annotate it to use a custom deserializer.

4. Create the custom deserializer.

5. Test the deserialization process with sample XML data.

3. Create a Maven Project

There are different ways to create a simple Maven project:

Create a Simple Maven Project using the Command Line Interface

Create a Simple Maven Project using  Eclipse IDE

Create a Simple Maven Project using  IntelliJ IDEA

4. Maven Dependencies

Open the pom.xml file, and add the following Jackson data binding dependency:

<dependency>
    <groupId>com.fasterxml.jackson.dataformat</groupId>
    <artifactId>jackson-dataformat-xml</artifactId>
    <version>2.13.0</version>
</dependency>

5. Code Program

import com.fasterxml.jackson.core.JsonParser;
import com.fasterxml.jackson.databind.DeserializationContext;
import com.fasterxml.jackson.databind.JsonDeserializer;
import com.fasterxml.jackson.databind.annotation.JsonDeserialize;
import com.fasterxml.jackson.dataformat.xml.XmlMapper;
class User {
    private String id;
    private String fullName;
    // Standard getters, setters, and constructor omitted for brevity
}

@JsonDeserialize(using = UserDeserializer.class)
class UserDeserializer extends JsonDeserializer<User> {
    @Override
    public User deserialize(JsonParser p, DeserializationContext ctxt) throws IOException {
        String id = p.nextTextValue();  // Assumes first field is the id
        String fullName = p.nextTextValue();  // Assumes second field is the fullName
        return new User(id, fullName);
    }
}

public class MainApp {
    public static void main(String[] args) {
        String xmlData = "<User><id>1</id><fullName>John Doe</fullName></User>";
        XmlMapper xmlMapper = new XmlMapper();
        try {
            User user = xmlMapper.readValue(xmlData, User.class);
            System.out.println("User ID: " + user.getId());
            System.out.println("User Name: " + user.getFullName());
        } catch (Exception e) {
            e.printStackTrace();
        }
    }
}

Output:

User ID: 1
User Name: John Doe

Code Explanation:

1. The User class represents a user entity. Here, it contains fields for ID and full name.

2. The UserDeserializer is our custom deserializer. It extends JsonDeserializer and overrides the deserialize method. This method provides the logic on how to extract and set the data from the XML into a User object.

3. Within the MainApp class, we provide a sample XML string to demonstrate the deserialization.

4. The XmlMapper is used to perform the conversion of the XML string into a User object using the custom deserializer.

5. The output displays the deserialized data.

6. Conclusion

Custom deserializers in Jackson empower developers to handle complex XML structures or scenarios where the default behavior doesn't align with the project's needs. With this flexibility, one can efficiently process XML data to fit the exact requirements of their application.

Check out all the Java Jackson JSON tutorials and examples: 50+ Java Jackson JSON Tutorials with Examples