Given a Spotify playlist URL, prints out a track listing.

SpotLister.java

import module java.base;
import module java.desktop;
import module java.net.http;
import java.util.List;

/**
 * The playlist contains meta tags with name attributes of "music:song", each is a URL
 * to a song page where the meta og:title is the track title and music:musician_description contains
 * the artist
 */
public class SpotLister 
{
    private Map <URI, String[]> tracks = new LinkedHashMap <> ();
    static int TITLE = 0, ARTIST = 1;
    static HttpClient client = HttpClient.newHttpClient();
    
    public SpotLister(URI uri)
    {
        try
        {
            var req = HttpRequest.newBuilder(uri).build();
            var res = HttpResponse.BodyHandlers.ofInputStream();

            delegate(client.send(req, res)); 
        
            var requests = tracks.keySet().stream()
            .map(HttpRequest::newBuilder)
            .map(HttpRequest.Builder::build)
            .toList();

            CompletableFuture.allOf(requests.stream()
            .map(request -> client.sendAsync(request, HttpResponse.BodyHandlers.ofInputStream())
            .thenAccept(response -> tracks.replace(response.request().uri(), delegate(response))))
            .toArray(CompletableFuture<?>[]::new))
            .join();
        }
        catch (IOException ex) 
        {
            throw new UncheckedIOException(ex);
        }
        catch (InterruptedException ex)
        {
            Thread.currentThread().interrupt();
            throw new RuntimeException(ex);
        }

        var i = 0;
        for (var track : tracks.values()) System.out.format("%d. %s / %s%n", ++i, track[TITLE], track[ARTIST]);
    }

    class Delegate extends HTMLEditorKit.ParserCallback
    {
        private String[] track = new String[2];

        @Override
        public void handleSimpleTag(HTML.Tag t, MutableAttributeSet s, int pos)
        {
    	    if (!(t.equals(HTML.Tag.META) && s.isDefined(HTML.Attribute.CONTENT))) return;
        
            var content = s.getAttribute(HTML.Attribute.CONTENT).toString();

            switch (String.valueOf(s.getAttribute(HTML.Attribute.NAME)))
            {
                case "music:song":
                tracks.put(URI.create(content), track);
                return;
                case "music:musician_description":
                track[ARTIST] = content;
                return;
            }
        
            var property = String.valueOf(s.getAttribute("property"));        
        
            if ("og:title".equals(property)) track[TITLE] = content;        
        }
    }

    String[] delegate(HttpResponse <InputStream> res)
    {
        var delegate = new Delegate();

        try
        {
            new ParserDelegator().parse(new InputStreamReader(res.body(), StandardCharsets.UTF_8), delegate, true);
        }
        catch (IOException ex)
        {
            throw new UncheckedIOException(ex); 		
        }    

        return delegate.track;
    }

    public static void main(String[] args)
    {
        Arrays.stream(args).map(URI::create).forEach(SpotLister::new);      
    }
}

Updated for latest Spotify html output, Dec 2022

Rewritten for new Spotify, July 2023

Updated, October 2023.

Updated for Java 25.