loklak_wok_android

Loklak Wok Android is a peer harvester that posts collected  messages to the Loklak Server. The suggestions to search tweets are fetched using suggest API endpoint. Using the suggestion queries, tweets are scraped. The scraped tweets are shown in a RecyclerView and simultaneously they are posted to loklak server using push API endpoint. Let’s see how this is implemented. Adding Dependencies to the project This feature heavily uses Retrofit2, Reactive extensions(RxJava2, RxAndroid and Retrofit RxJava adapter) and RetroLambda (for Java lambda support in Android). In app/build.gradle: apply plugin: 'com.android.application' apply plugin: 'me.tatarka.retrolambda' android { ... packagingOptions { exclude 'META-INF/rxjava.properties' } } dependencies { ... compile 'com.google.code.gson:gson:2.8.1' compile 'com.squareup.retrofit2:retrofit:2.3.0' compile 'com.squareup.retrofit2:converter-gson:2.3.0' compile 'com.squareup.retrofit2:adapter-rxjava2:2.3.0' compile 'io.reactivex.rxjava2:rxjava:2.0.5' compile 'io.reactivex.rxjava2:rxandroid:2.0.1' }   In build.gradle project level: dependencies { classpath 'com.android.tools.build:gradle:2.3.3' classpath 'me.tatarka:gradle-retrolambda:3.2.0' }   Implementation The suggest and push API endpoint is defined in LoklakApi interface public interface LoklakApi { @GET("/api/suggest.json") Observable<SuggestData> getSuggestions(@Query("q") String query, @Query("count") int count); @POST("/api/push.json") @FormUrlEncoded Observable<Push> pushTweetsToLoklak(@Field("data") String data); }   The POJOs (Plain Old Java Objects) for suggestions and posting tweets are obtained using jsonschema2pojo, Gson uses POJOs to convert JSON to Java objects. The REST client is created by Retrofit2 and is implemented in RestClient class. The Gson converter and RxJava adapter for retrofit is added in the retrofit builder. create method is called to generate the API methods(retrofit implements LoklakApi Interface). public class RestClient { private RestClient() { } private static void createRestClient() { sRetrofit = new Retrofit.Builder() .baseUrl(BASE_URL) // gson converter .addConverterFactory(GsonConverterFactory.create(gson)) // retrofit adapter for rxjava .addCallAdapterFactory(RxJava2CallAdapterFactory.create()) .build(); } private static Retrofit getRetrofitInstance() { if (sRetrofit == null) { createRestClient(); } return sRetrofit; } public static <T> T createApi(Class<T> apiInterface) { // create method to generate API methods return getRetrofitInstance().create(apiInterface); } }   The suggestions are fetched by calling getSuggestions after LoklakApi interface is implemented. getSuggestions returns an Observable of type SuggestData, which contains the suggestions in a List. For scraping tweets only a single query needs to be passed to LiquidCore, so flatmap is used to transform the observabe and then fromIterable operator is used to emit single queries as string to LiquidCore which then scrapes tweets, as implemented in fetchSuggestions private Observable<String> fetchSuggestions() { LoklakApi loklakApi = RestClient.createApi(LoklakApi.class); Observable<SuggestData> observable = loklakApi.getSuggestions("", 2); return observable.flatMap(suggestData -> { List<Query> queryList = suggestData.getQueries(); List<String> queries = new ArrayList<>(); for (Query query : queryList) { queries.add(query.getQuery()); } return Observable.fromIterable(queries); }); }   As LiquidCore uses callbacks to create a connection between NodeJS instance and Android, to maintain a flow of observables a custom observable is created using create operator which encapsulates the callbacks inside it. For a detail understanding of how LiquidCore event handling works, please go through the example. The way it is implemented in getScrapedTweets: private Observable<ScrapedData> getScrapedTweets(final String query) { final String LC_TWITTER_URI = "android.resource://org.loklak.android.wok/raw/twitter"; URI uri = URI.create(LC_TWITTER_URI); return Observable.create(emitter -> { // custom observable creation EventListener startEventListener = (service, event, payload) -> { service.emit(LC_QUERY_EVENT, query); service.emit(LC_FETCH_TWEETS_EVENT); }; EventListener getTweetsEventListener = (service, event, payload) -> { ScrapedData scrapedData = mGson.fromJson(payload.toString(), ScrapedData.class);…