record Bar(int id);

interface Foo {
    // returns some domain entity
    // if it doesnt exist return null
    // if it cannot be obtained due to system error throw runtime exception
    Bar getBarById(int id);
}

class ConcreteFoo implements Foo {
    public Bar getBarById(int id) {
        return new Bar(id);
    }
}

class HttpClientFoo implements Foo {
    private HttpClient client;
    public HttpClientFoo(HttpClient client) {
        this.client = client;
    }

    public Bar getBarById(int id) {
        // suppose client is raw http client that returns string
        try {
            Response<String> externalResult = this.client.get("/api/foo/" + id);
            if(externalResult.isSuccessful()) {
                String body = externalResult.body();
                // suppose some parsing method exists and returns Bar
                return parseBody(body);
            }
            return null;
        }
        catch (Exception e) {
            throw new RuntimeException(e);
        }
    }
}

class ControllerFoo implements Foo {
    private Foo delegate;
    public ControllerFoo(Foo delegate) {
        this.delegate = delegate;
    }

    @GET
    @Path("/api/foo/{id}")
    public Bar getBarById(@PathParam("id") int id) {
        return delegate.getBarById(id);
    }
}

class Main {
    public static void main(String args[]) {
        Foo concreteFoo = new ConcreteFoo();
        Foo controller = new ControllerFoo(concreteFoo);
        Server.listen(3000)
            .controler(controler) // suppose theres a server utility class to host servers
    }
}