pitfalls in builder inside singleton method controller

Lets say I have controller RequestController in Spring which is marked as Singleton. Inside this controller there is a biulder which is injected usinf dependency injection. The main goal for this class is to reveive requests and build responses.

@Singleton
class RequestController {
    private ResponseBuilder responseBuilder;

    private RequestController(ResponseBuilder responseBuilder){
        this.responseBuilder=responseBuilder;
    }

    public Response getResponse(Request request) {
        return responseBuilder.getRequest(request).build();
    }
}

My question: What kind of pitfalls this code hide. What could go wrong when we try to use it in normal spring application. @Singleton is only an information that this class will be created only once per applications. I know that builder should be thread-safe since it will be responsible for handle multiple requests. But is anything else dangerous here?