UndertowServer.java

import io.undertow.Handlers;
import io.undertow.Undertow;
import io.undertow.server.handlers.*;
import io.undertow.util.Headers;
import org.apache.logging.log4j.LogManager;
import org.apache.logging.log4j.Logger;

public class UndertowServer {
    public static void main(String[] args) {
        Logger logger = LogManager.getLogger(UndertowServer.class);

        PathHandler pathHandler = Handlers.path()
                .addExactPath("/", exchange -> {
                    exchange.getResponseHeaders().put(Headers.CONTENT_TYPE, "text/plain");
                    exchange.getResponseSender().send("Hello World");
                })
                .addExactPath("/err", exchange -> {
                    throw new IllegalArgumentException("Error");
                });


        ExceptionHandler exceptionHandler = Handlers.exceptionHandler(pathHandler)
                .addExceptionHandler(Exception.class, exchange -> {
                    Throwable attachment = exchange.getAttachment(ExceptionHandler.THROWABLE);
                    exchange.getResponseSender().send("Exception handled: " + attachment.getMessage());
                });


        GracefulShutdownHandler rootHandler = Handlers.gracefulShutdown(new StuckThreadDetectionHandler.Wrapper().wrap(exceptionHandler));

        Undertow undertow = Undertow.builder()
                .addHttpListener(8080, "localhost")
                .setHandler(rootHandler)
                .build();

        Runtime.getRuntime().addShutdownHook(new Thread(() -> {
            logger.info("Shutdown");
            rootHandler.shutdown();
            rootHandler.addShutdownListener(isSuccessful -> undertow.stop());

            try {
                rootHandler.awaitShutdown();
            } catch (InterruptedException e) {
                e.printStackTrace();
            }
            logger.info("Done");
        }));

        undertow.start();
    }
}