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