Spring Rest Controller Return Specific Fields

Being aware that my answer comes quite late: I'd recommend to look at Projections.

What you're asking for is what projections are about.

Since you're asking about Spring I'd give this one a try: https://docs.spring.io/spring-data/rest/docs/current/reference/html/#projections-excerpts

A very dynamic way for providing different projections on demand is offered by GraphQL. I just came across a very helpful article about how to use GraphQL with SpringBoot: https://www.graphql-java.com/tutorials/getting-started-with-spring-boot/

Instead of returning a Game object, you could serialize it as as a Map<String, Object>, where the map keys represent the attribute names. So you can add the values to your map based on the include parameter.

@ResponseBody
public Map<String, Object> getGame(@PathVariable("id") long id, String include) {

    Game game = service.loadGame(id);
    // check the `include` parameter and create a map containing only the required attributes
    Map<String, Object> gameMap = service.convertGameToMap(game, include);

    return gameMap;

}

As an example, if you have a Map<String, Object> like this:

gameMap.put("id", game.getId());
gameMap.put("title", game.getTitle());
gameMap.put("publishers", game.getPublishers());

It would be serialized like this:

{
  "id": 1,
  "title": "Call of Duty Advanced Warfare",
  "publishers": [
    {
        "id": 1,
        "name": "Activision"
    }
  ]
}