How to use dynamic property names for a Json object

Question

How can we make the JSON property name dynamic. For example

public class Value {
    @JsonProperty(value = "value")
    private String val;

    public void setVal(String val) {
        this.val = val;
    }

    public String getVal() {
        return val;
    }
}

when serializing this object it's saved as {"value": "actual_value_saved"} but I want to make the key also dynamic like {"new_key": "actual_value_saved"}. Any help is much appreciated.

Answer 1

You can use JsonAnySetter JsonAnyGetter annotations. Behind you can use Map instance. In case you have always one-key-object you can use Collections.singletonMap in other case use HashMap or other implementation. Below example shows how easy you can use this approach and create as many random key-s as you want:

import com.fasterxml.jackson.annotation.JsonAnyGetter;
import com.fasterxml.jackson.annotation.JsonAnySetter;
import com.fasterxml.jackson.databind.ObjectMapper;
import java.util.Collections;
import java.util.Map;
import java.util.Objects;

public class JsonApp {

    public static void main(String[] args) throws Exception {
        DynamicJsonsFactory factory = new DynamicJsonsFactory();
        ObjectMapper mapper = new ObjectMapper();

        System.out.println(mapper.writeValueAsString(factory.createUser("Vika")));
        System.out.println(mapper.writeValueAsString(factory.createPhone("123-456-78-9")));
        System.out.println(mapper.writeValueAsString(factory.any("val", "VAL!")));
    }
}

class Value {

    private Map<String, String> values;

    @JsonAnySetter
    public void put(String key, String value) {
        values = Collections.singletonMap(key, value);
    }

    @JsonAnyGetter
    public Map<String, String> getValues() {
        return values;
    }

    @Override
    public String toString() {
        return values.toString();
    }
}

class DynamicJsonsFactory {

    public Value createUser(String name) {
        return any("name", name);
    }

    public Value createPhone(String number) {
        return any("phone", number);
    }

    public Value any(String key, String value) {
        Value v = new Value();
        v.put(Objects.requireNonNull(key), Objects.requireNonNull(value));

        return v;
    }
}

Above code prints:

{"name":"Vika"}
{"phone":"123-456-78-9"}
{"val":"VAL!"}

Answer 2

You could have all the possible names as variables, and annotate them so they are ignored if null. This way you only get in your JSON the one that has a value

Then change your setter to feed into the variable mapped to the key you want.

class Value {

    @JsonProperty("val")
    @JsonInclude(JsonInclude.Include.NON_NULL)
    private String val;

    @JsonProperty("new_key")
    @JsonInclude(JsonInclude.Include.NON_NULL)
    private String newKey;

    @JsonProperty("any_random_string")
    @JsonInclude(JsonInclude.Include.NON_NULL)
    private String anyRandomString;

    public void setVal(String s) {
        if(/* condition1 */)
            this.val = s;
        else if (/* condition2 */) {
            this.newKey = s;
        } else  if (/* condition3 */) {
            this.anyRandomString = s;
        }
    }

}