How to Serialize and Deserialize Dynamic Properties with Jackson’s @JsonAnyGetter and @JsonAnySetter

1. @JsonAnyGetter

Jackson’s @JsonAnyGetter annotation marks a method that returns a Map of dynamic properties to be included in the JSON output during serialization.

1.1 Requirements

Method must be public.

Method must have no parameters.

Return type must be Map<String, Object> or a subclass.

1.2 Usage

Example:

import com.fasterxml.jackson.annotation.JsonAnyGetter;
import com.fasterxml.jackson.databind.ObjectMapper;
import java.util.HashMap;
import java.util.Map;

class User {
    private String name;
    private int age;
    private Map<String, Object> dynamicProps;

    public User(String name, int age) {
        this.name = name;
        this.age = age;
        this.dynamicProps = new HashMap<>();
    }

    public String getName() { return name; }
    public int getAge() { return age; }

    @JsonAnyGetter
    public Map<String, Object> getDynamicProps() {
        return dynamicProps;
    }
}

public class Example {
    public static void main(String[] args) throws Exception {
        User user = new User("John", 30);
        user.getDynamicProps().put("email", "[email protected]");
        user.getDynamicProps().put("phone", "+1 123-456-7890");

        ObjectMapper objectMapper = new ObjectMapper();
        String json = objectMapper.writeValueAsString(user);
        System.out.println(json);
    }
}

The User class contains two regular fields and a Map called dynamicProps. Adding entries for “email” and “phone” to the map and annotating the getter with @JsonAnyGetter causes Jackson to output those entries as top‑level JSON fields.

During serialization Jackson invokes the annotated method and merges the returned key‑value pairs into the generated JSON.

2. @JsonAnySetter

@JsonAnySetter tells Jackson to call the annotated method for each JSON property that does not match a regular field, allowing dynamic properties to be stored in the object.

2.1 Requirements

Method must be public.

Method must accept a String key and an Object value as parameters.

Method must have a void return type.

2.2 Usage

Example:

import com.fasterxml.jackson.annotation.JsonAnySetter;
import com.fasterxml.jackson.databind.ObjectMapper;
import java.util.HashMap;
import java.util.Map;

class User {
    private String name;
    private int age;
    private Map<String, Object> dynamicProps;

    public User() {
        this.dynamicProps = new HashMap<>();
    }

    public String getName() { return name; }
    public void setName(String name) { this.name = name; }
    public int getAge() { return age; }
    public void setAge(int age) { this.age = age; }

    @JsonAnySetter
    public void setDynamicProp(String key, Object value) {
        dynamicProps.put(key, value);
    }

    public Map<String, Object> getDynamicProps() {
        return dynamicProps;
    }
}

public class Example {
    public static void main(String[] args) throws Exception {
        String json = "{\"name\":\"John\",\"age\":30,\"email\":\"[email protected]\",\"phone\":\"+1 123-456-7890\"}";
        ObjectMapper objectMapper = new ObjectMapper();
        User user = objectMapper.readValue(json, User.class);
        System.out.println("Name: " + user.getName());
        System.out.println("Age: " + user.getAge());
        System.out.println("Dynamic Properties: " + user.getDynamicProps());
    }
}

The User class again has a Map for dynamicProps. Annotating setDynamicProp with @JsonAnySetter makes Jackson call this method for each unknown JSON field, storing them in the map. This enables the object to receive and handle dynamic properties without predefined fields.