java - Serialization of key/value pairs in Jackson?

Question

I have a class

class Foo {
  String key;
  String value;
}

and want to serialize this into "<content of key>":"<content of value>" How can I achieve this (and how to deserialize "myKey":"myVal" into a Fooobject?

I was trying to use

@JsonValue
public String toString() {
   return """ + key + "":"" + value + """;
}

But clearly end up with too many quotes.

@JsonValue
public String toString() {
    return key + ":" + value;
}

also does not work, as it does not create enough quotes.

Answer 1

I found one way, which is using a JsonSerializer like this:

public class PropertyValueSerializer extends JsonSerializer<Foo> {

    @Override
    public void serialize(Foo property_value, JsonGenerator jsonGenerator,
                          SerializerProvider serializerProvider) throws IOException, JsonProcessingException {

        jsonGenerator.writeStartObject();
        jsonGenerator.writeFieldName(property_value.getKey());
        jsonGenerator.writeString(property_value.getValue());
        jsonGenerator.writeEndObject();
    }

The Foo class needs to know about this:

@JsonSerialize(using = PropertyValueSerializer.class)
public class Foo {

Deserializing is very similar:

public class PropertyValueDeserializer extends JsonDeserializer<PROPERTY_VALUE> {    

    @Override
    public Foo deserialize(JsonParser jsonParser,
                                      DeserializationContext deserializationContext) throws IOException, JsonProcessingException {

        String tmp = jsonParser.getText(); // {
        jsonParser.nextToken();
        String key = jsonParser.getText();
        jsonParser.nextToken();
        String value = jsonParser.getText();
        jsonParser.nextToken();
        tmp = jsonParser.getText(); // }

        Foo pv = new Foo(key,value);
        return pv;
    }

And this also needs to be annotated on the Foo class:

@JsonSerialize(using = PropertyValueSerializer.class)
@JsonDeserialize(using = PropertyValueDeserializer.class)
public class Foo implements Serializable{