Fallback example

FallBackExample.java

import okhttp3.OkHttpClient;
import okhttp3.Request;

import java.io.IOException;
import java.time.Duration;
import java.util.ArrayList;
import java.util.List;
import java.util.Optional;

public class FallBackExample {
    private static final List<List<String>> listOfUrls = List.of(
            List.of("http://www.invalidurl.com", "http://www.invalidurl.com", "http://www.google.com"),
            List.of("http://www.invalidurl.com", "http://www.yahoo.com", "http://www.bb2.com"),
            List.of("http://www.google.com", "http://www.invalidurl.com", "http://www.invalidurl.com"),
            List.of("http://www.invalidurl.com", "http://www.invalidurl.com", "http://www.bbc.com"),
            List.of("http://www.invalidurl.com", "http://www.cnn.com", "http://www.invalidurl.com"),
            List.of("http://www.cnbc.com", "http://www.invalidurl.com", "http://www.invalidurl.com"),
            List.of("http://www.invalidurl.com", "http://www.invalidurl.com", "http://www.dw.com"),
            List.of("http://www.invalidurl.com", "http://www.youtube.com", "http://www.invalidurl.com"),
            List.of("http://www.toi.com", "http://www.invalidurl.com", "http://www.invalidurl.com"));

    private static List<String> getValidFallbackUrls(List<List<String>> listOfUrls) {
        List<String> urlList = new ArrayList<>();
        listOfUrls.parallelStream().forEach(listOfUrl -> getOutPut(listOfUrl.get(0)).ifPresentOrElse(urlList::add,
                () -> getOutPut(listOfUrl.get(1)).ifPresentOrElse(urlList::add,
                        () -> getOutPut(listOfUrl.get(2)).ifPresent(urlList::add))));
        return urlList;
    }

    private static Optional<String> getOutPut(String url) {
        OkHttpClient client = new OkHttpClient().newBuilder()
                .connectTimeout(Duration.ofSeconds(5))
                .readTimeout(Duration.ofSeconds(5))
                .writeTimeout(Duration.ofSeconds(5))
                .build();
        Request request = new Request.Builder()
                .url(url)
                .method("GET", null)
                .build();
        try {
            client.newCall(request).execute();
            Thread.currentThread().interrupt();
            return Optional.of(url);
        } catch (IOException e) {
            return Optional.empty();
        }
    }

    public static void main(String[] args) {
        final var validFallbackUrls = getValidFallbackUrls(listOfUrls);
        validFallbackUrls.forEach(System.out::println);
    }
}