public void save() { try { File file = getFile(); if (!file.exists()) // noinspection ResultOfMethodCallIgnored file.createNewFile(); JsonObject rootObject = new JsonObject(); JsonArray players = new JsonArray(); for (Player player : playerDB.values()) players.add(player.toJson()); rootObject.add("players", players); JsonArray groups = new JsonArray(); for (Group group : groupDB.values()) groups.add(group.toJson()); rootObject.add("groups", groups); BufferedWriter bw = new BufferedWriter(new FileWriter(file)); bw.write(GSON.toJson(rootObject)); bw.close(); } catch (IOException e) { e.printStackTrace(); } }