Jackson: jackson Mix- In Annotations

Annotations are a great way to manage serialization and deserialization in Jackson. However, what do you do if you want to annotate a third party class, or if you dont want to tightly couple your POJOs to jackson annotations. This is where Mix-in comes into play. You define a mix-in abstract class that is kind of a proxy to the actual class. Annotations are then definied over this proxy class

Jackson Mix-In Example

package com.studytrails.json.jackson;

import java.io.File;
import java.io.IOException;

import com.fasterxml.jackson.core.JsonGenerationException;
import com.fasterxml.jackson.databind.JsonMappingException;
import com.fasterxml.jackson.databind.ObjectMapper;

public class SerializeExample3 {
    public static void main(String[] args) throws JsonGenerationException, JsonMappingException, IOException {
        ObjectMapper mapper = new ObjectMapper();
        mapper.addMixInAnnotations(Bird.class, BirdMixIn.class);
        Bird bird = new Bird("scarlet Ibis");
        bird.setSound("eee");
        bird.setHabitat("water");

        mapper.writerWithDefaultPrettyPrinter().writeValue(new File("bird.json"), bird);
    }

}

The Bird class

package com.studytrails.json.jackson;

public class Bird {

    private String name;
    private String sound;
    private String habitat;

    public Bird(String name) {
        this.name = name;
    }

    public String getName() {
        return name;
    }

    public String getSound() {
        return sound;
    }

    public String getHabitat() {
        return habitat;
    }

    public void setSound(String sound) {
        this.sound = sound;
    }

    public void setHabitat(String habitat) {
        this.habitat = habitat;
    }

    @Override
    public String toString() {
        return "Bird [name=" + name + ", sound=" + sound + ", habitat=" + habitat + "]";
    }
}

The Mix-in class

package com.studytrails.json.jackson;

import com.fasterxml.jackson.annotation.JsonProperty;

public abstract class BirdMixIn {
    BirdMixIn(@JsonProperty("name") String name) {
    };

    @JsonProperty("sound")
    abstract String getSound();

    @JsonProperty("habitat")
    abstract String getHabitat();
}

(Note: This article’s original links is here )

 Jackson: Json data binding filters Jackson: Json Polymorphism 

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