Java Jackson @JsonManagedReference

1. Overview

When working with Jackson for JSON serialization/deserialization, developers often face challenges when dealing with bidirectional relationships in object models, such as the relationship between parents and their children. Infinite recursion is a common issue in this scenario. Jackson provides annotations like @JsonManagedReference and @JsonBackReference to handle these cases efficiently. In this article, we'll examine the @JsonManagedReference annotation, with a User Management System as an example.

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

@JsonManagedReference Annotation Overview

The @JsonManagedReference annotation is used to annotate the property that manages the relationship. It helps Jackson navigate these relationships without falling into infinite loops. The other side of the relation would be annotated with @JsonBackReference.

2. Development Steps

1. Set up a new Maven project.

2. Add the necessary Jackson dependencies.

3. Define the entity classes, one of which utilizes the @JsonManagedReference annotation.

4. Create a main class to demonstrate serialization.

5. Serialize an example object to JSON.

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

// Address.java
public class Address {
    private String city;
    private String country;
    @JsonBackReference
    private User user;
    // Constructors, getters, setters...
}
// User.java
public class User {
    private int id;
    private String name;
    @JsonManagedReference
    private Address address;
    // Constructors, getters, setters...
}
// MainDemo.java
import com.fasterxml.jackson.databind.ObjectMapper;
public class MainDemo {
    public static void main(String[] args) {
        Address address = new Address("New York", "USA");
        User user = new User(1, "Alice", address);
        address.setUser(user);
        ObjectMapper mapper = new ObjectMapper();
        try {
            String json = mapper.writeValueAsString(user);
            System.out.println(json);
        } catch (Exception e) {
            e.printStackTrace();
        }
    }
}

Output:

{"id":1,"name":"Alice","address":{"city":"New York","country":"USA"}}

Code Explanation:

In our model, a User has an Address, and conversely, an Address references a User. This creates a bidirectional relationship.

The @JsonManagedReference annotation on the address property in the User class indicates that this field should be serialized, while the corresponding backreference @JsonBackReference in the Address class indicates that the user field should not be serialized to prevent infinite recursion.

When serializing the User object in our main demonstration, Jackson serializes the address property but avoids serializing the back reference to user in the Address class, thus eliminating any infinite loop scenario.

6. Conclusion

Jackson's @JsonManagedReference and @JsonBackReference annotations are invaluable tools for managing and navigating bidirectional relationships in Java entities during JSON serialization/deserialization. They prevent infinite recursion issues and ensure efficient data representation. When used wisely, they can handle complex object relationships seamlessly.

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