Force Jackson to add addional wrapping using annotations

Question

I have the following class:

public class Message {
    private String text;

    public String getText() {
        return text;
    }

    public void setText(St         


        

Answer 1

It was sad to learn that you must write custom serialization for the simple goal of wrapping a class with a labeled object. After playing around with writing a custom serializer, I concluded that the simplest solution is a generic wrapper. Here's perhaps a more simple implementation of your example above:

public final class JsonObjectWrapper {
    private JsonObjectWrapper() {}

    public static <E> Map<String, E> withLabel(String label, E wrappedObject) {
        HashMap<String, E> map = new HashMap<String, E>();
        map.put(label, wrappedObject);
        return map;
    }
}

Answer 2

With Jackson 2.x use can use the following to enable wrapper without adding addition properties in the ObjectMapper

import com.fasterxml.jackson.annotation.JsonTypeInfo;
import com.fasterxml.jackson.annotation.JsonTypeName;

@JsonTypeInfo(include = JsonTypeInfo.As.WRAPPER_OBJECT, use = JsonTypeInfo.Id.NAME)
@JsonTypeName(value = "student")
public class Student {
  private String name;
  private String id;
}

Answer 3

Provided you don't mind the json having a capital m in message, then the simplest way to do this is to annotate your class with @JsonTypeInfo.

You would add:

@JsonTypeInfo(include=As.WRAPPER_OBJECT, use=Id.NAME)
public class Message {
  // ...
}

to get {"Message":{"text":"Text"}}

Answer 4

If using spring, then in application.properties file add following:-

spring.jackson.serialization.WRAP_ROOT_VALUE=true

And then use @JsonRootName annotation on any of your class that you wish to serialize. e.g.

@JsonRootName("user")
public class User {
    private String name;
    private Integer age;
}

Answer 5

I have created a small jackson module that contains a @JsonWrapped annotation, that solves the problem. See here for the code: https://github.com/mwerlitz/jackson-wrapped

Your class would then look like:

public class Message {
    @JsonWrapped("message")
    private String text;
}

Answer 6

A Simpler/Better way to do it:

@JsonRootName(value = "message")
public class Message { ...}

then use
new ObjectMapper().configure(SerializationFeature.WRAP_ROOT_VALUE, true).writeValueAs...