CreatStore.kt

Store<Article, Integer> store = StoreBuilder.<Integer, BufferedSource, Article>parsedWithKey()
        .fetcher(articleId -> api.getArticles(articleId)) 
        .persister(FileSystemPersister.create(FileSystemFactory.create(context.getFilesDir()), pathResolver))
        .parser(GsonParserFactory.createSourceParser(gson, String.class))
        .open();