API REQUEST GET

public class MojangAPI {
    private static final String USER_API_REQ = "https://api.mojang.com/users/profiles/minecraft/%s";

    private Map<String, UUID> responseCache = new ConcurrentHashMap<String, UUID>();

    private UUID getOfflineUUID(String name) {
        if (!responseCache.containsKey(name)) {
            try {
                HttpURLConnection con = (HttpURLConnection) new URL(String.format(USER_API_REQ, name)).openConnection();
                con.setRequestMethod("GET");
                int code = con.getResponseCode();
                if (code == 204) {
                    System.out.println("Mojang API server returned 204 code! (User does not exist!)");
                    return null;
                } else if (code == 404) {
                    System.out.println("Mojang API returned 404! (Server not found)");
                }
                InputStreamReader reader = new InputStreamReader(con.getInputStream());
                JsonElement element = new JsonParser().parse(reader);
                if (element.isJsonArray()) {
                    System.out.println("Link returned invalid JSON (returned an array)");
                    return null;
                }
                reader.close();
                JsonObject obj = element.getAsJsonArray().get(0).getAsJsonObject();
                UUID finallly = UUID.fromString(obj.get("id").getAsString());
                responseCache.put(name, finallly);
                return finallly;
            } catch (Exception e) {
                e.printStackTrace();
            }
            return null;
        } else {
            return responseCache.get(name);
        }
    }

    public UUID getOfflineUUIDAsync(String name) {
        CompletableFuture<UUID> unique = CompletableFuture.supplyAsync(() -> getOfflineUUID(name), Constants.DEFAULT_THREAD_POOL);
        try {
            return unique.get();
        } catch (InterruptedException | ExecutionException e) {
            e.printStackTrace();
        }
        return null;
    }

}