Java Jackson @JsonIgnoreProperties

1. Overview

Jackson is a popular library in Java for JSON processing, providing capabilities to serialize and deserialize Java objects to and from JSON. One common challenge developers face when working with JSON is handling unknown or unwanted fields in the payload. The @JsonIgnoreProperties annotation in Jackson offers a neat solution for this challenge. This blog post explores its application in a User Management System.

@JsonIgnoreProperties Annotation Overview

The @JsonIgnoreProperties annotation allows for specifying which properties should be ignored during serialization and deserialization. It can be used both at the class level and at the field level. When used at the class level, it specifies properties of the class that Jackson will ignore. At the field level, it specifies properties of the referenced class to be ignored.

2. Development Steps

1. Set up a new Maven project.

2. Add the necessary Jackson dependencies.

3. Create a User class utilizing the @JsonIgnoreProperties annotation.

4. Develop a main class for demonstration.

5. Deserialize sample JSON data into the User object.

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.core</groupId>
    <artifactId>jackson-databind</artifactId>
    <version>2.13.0</version>
</dependency>

5. Code Program

// User.java
@JsonIgnoreProperties(ignoreUnknown = true)
public class User {
    private int id;
    private String username;
    private String email;
    // Constructors, getters, setters...
}
// MainDemo.java
import com.fasterxml.jackson.databind.ObjectMapper;
public class MainDemo {
    public static void main(String[] args) {
        String json = "{\"id\": 1, \"username\": \"johndoe\", \"email\": \"[email protected]\", \"phone\": \"1234567890\"}";
        ObjectMapper mapper = new ObjectMapper();
        try {
            User user = mapper.readValue(json, User.class);
            System.out.println("User ID: " + user.getId() + ", Username: " + user.getUsername() + ", Email: " + user.getEmail());
        } catch (Exception e) {
            e.printStackTrace();
        }
    }
}

Output:

User ID: 1, Username: johndoe, Email: [email protected]

Code Explanation:

The User class is annotated with @JsonIgnoreProperties(ignoreUnknown = true). This means that during deserialization, if the JSON contains any fields that are not present in the User class (like the "phone" field in our example), Jackson will ignore them without throwing an exception.

In the MainDemo class, we provide a JSON string that includes an additional "phone" field not present in the User class. Thanks to the annotation, our program deserializes the JSON without any issues, ignoring the unwanted "phone" field.

6. Conclusion

The @JsonIgnoreProperties annotation in Jackson is an invaluable tool when working with JSON data that might have extra, unwanted, or unknown properties. By ensuring seamless deserialization, even when confronted with unexpected data, it aids in creating resilient and adaptable applications.