Modern Java in Action

public sealed interface Page
        permits ErrorPage, SuccessfulPage {

    URI url();

}

public record GitHubPrPage(
    URI url, String content, Set<Page> links, int number)
    implements GitHubPage {

    public GitHubPrPage {
        // argument validation
    }

    public GitHubPrPage(
            URI url, String content, int number) {
        this(url, content, new HashSet<>(), number);
    }

    // `equals` and `hashcode` based on `url`

}

public static String pageName(Page page) {
    return switch (page) {
        case ErrorPage(var url, _)
            -> "💥 ERROR: " + url.getHost();
        case ExternalPage(var url, _)
            -> "💤 EXTERNAL: " + url.getHost();
        case GitHubIssuePage(_, _, _, int number)
            -> "🐈 ISSUE #" + number;
        case GitHubPrPage(_, _, _, int number)
            -> "🐙 PR #" + number;
    };
}

// creation
var client = HttpClient.newHttpClient();

// use
var request = HttpRequest
    .newBuilder(url)
    .GET()
    .build();
return client
    .send(request, BodyHandlers.ofString())
    .body();

try (var scope =
        new StructuredTaskScope.ShutdownOnFailure()) {
    var futurePages = links.stream()
        .map(link -> scope.fork(
            () -> createPage(link, depth)))
        .toList();

    scope.join();
    scope.throwIfFailed();

    return futurePages.stream()
        .map(Subtask::get)
        .collect(toSet());
} catch (ExecutionException ex) {
    // [...]
}

SimpleFileServer.createFileServer(
        address,
        serverDir.toAbsolutePath(),
        OutputLevel.INFO)
    .start();

java -p jars $mainClass $args