Add nullability annotations to module/spring-boot-undertow

See gh-46587

module/spring-boot-undertow/src/main/java/org/springframework/boot/undertow/AccessLogHttpHandlerFactory.java

@@ -25,13 +25,12 @@ import io.undertow.Undertow;
 import io.undertow.server.HttpHandler;
 import io.undertow.server.handlers.accesslog.AccessLogHandler;
 import io.undertow.server.handlers.accesslog.DefaultAccessLogReceiver;
+import org.jspecify.annotations.Nullable;
 import org.xnio.OptionMap;
 import org.xnio.Options;
 import org.xnio.Xnio;
 import org.xnio.XnioWorker;
 
-import org.springframework.util.Assert;
-
 /**
  * An {@link HttpHandlerFactory} for an {@link AccessLogHandler}.
  *
@@ -41,15 +40,16 @@ class AccessLogHttpHandlerFactory implements HttpHandlerFactory {
 
 	private final File directory;
 
-	private final String pattern;
+	private final @Nullable String pattern;
 
-	private final String prefix;
+	private final @Nullable String prefix;
 
-	private final String suffix;
+	private final @Nullable String suffix;
 
 	private final boolean rotate;
 
-	AccessLogHttpHandlerFactory(File directory, String pattern, String prefix, String suffix, boolean rotate) {
+	AccessLogHttpHandlerFactory(File directory, @Nullable String pattern, @Nullable String prefix,
+			@Nullable String suffix, boolean rotate) {
 		this.directory = directory;
 		this.pattern = pattern;
 		this.prefix = prefix;
@@ -58,7 +58,7 @@ class AccessLogHttpHandlerFactory implements HttpHandlerFactory {
 	}
 
 	@Override
-	public HttpHandler getHandler(HttpHandler next) {
+	public HttpHandler getHandler(@Nullable HttpHandler next) {
 		try {
 			createAccessLogDirectoryIfNecessary();
 			XnioWorker worker = createWorker();
@@ -74,7 +74,6 @@ class AccessLogHttpHandlerFactory implements HttpHandlerFactory {
 	}
 
 	private void createAccessLogDirectoryIfNecessary() {
-		Assert.state(this.directory != null, "Access log directory is not set");
 		if (!this.directory.isDirectory() && !this.directory.mkdirs()) {
 			throw new IllegalStateException("Failed to create access log directory '" + this.directory + "'");
 		}
@@ -94,8 +93,8 @@ class AccessLogHttpHandlerFactory implements HttpHandlerFactory {
 
 		private final XnioWorker worker;
 
-		ClosableAccessLogHandler(HttpHandler next, XnioWorker worker, DefaultAccessLogReceiver accessLogReceiver,
-				String formatString) {
+		ClosableAccessLogHandler(@Nullable HttpHandler next, XnioWorker worker,
+				DefaultAccessLogReceiver accessLogReceiver, String formatString) {
 			super(next, accessLogReceiver, formatString, Undertow.class.getClassLoader());
 			this.worker = worker;
 			this.accessLogReceiver = accessLogReceiver;

module/spring-boot-undertow/src/main/java/org/springframework/boot/undertow/CompressionHttpHandlerFactory.java

@@ -29,6 +29,7 @@ import io.undertow.server.handlers.encoding.EncodingHandler;
 import io.undertow.server.handlers.encoding.GzipEncodingProvider;
 import io.undertow.util.Headers;
 import io.undertow.util.HttpString;
+import org.jspecify.annotations.Nullable;
 
 import org.springframework.boot.web.server.Compression;
 import org.springframework.http.HttpHeaders;
@@ -51,7 +52,7 @@ class CompressionHttpHandlerFactory implements HttpHandlerFactory {
 	}
 
 	@Override
-	public HttpHandler getHandler(HttpHandler next) {
+	public @Nullable HttpHandler getHandler(@Nullable HttpHandler next) {
 		if (!this.compression.getEnabled()) {
 			return next;
 		}

module/spring-boot-undertow/src/main/java/org/springframework/boot/undertow/ConfigurableUndertowWebServerFactory.java

@@ -20,6 +20,7 @@ import java.io.File;
 import java.util.Collection;
 
 import io.undertow.Undertow.Builder;
+import org.jspecify.annotations.Nullable;
 
 import org.springframework.boot.web.server.ConfigurableWebServerFactory;
 
@@ -50,49 +51,49 @@ public interface ConfigurableUndertowWebServerFactory extends ConfigurableWebSer
 	 * Set the buffer size.
 	 * @param bufferSize buffer size
 	 */
-	void setBufferSize(Integer bufferSize);
+	void setBufferSize(@Nullable Integer bufferSize);
 
 	/**
 	 * Set the number of IO Threads.
 	 * @param ioThreads number of IO Threads
 	 */
-	void setIoThreads(Integer ioThreads);
+	void setIoThreads(@Nullable Integer ioThreads);
 
 	/**
 	 * Set the number of Worker Threads.
 	 * @param workerThreads number of Worker Threads
 	 */
-	void setWorkerThreads(Integer workerThreads);
+	void setWorkerThreads(@Nullable Integer workerThreads);
 
 	/**
 	 * Set whether direct buffers should be used.
 	 * @param useDirectBuffers whether direct buffers should be used
 	 */
-	void setUseDirectBuffers(Boolean useDirectBuffers);
+	void setUseDirectBuffers(@Nullable Boolean useDirectBuffers);
 
 	/**
 	 * Set the access log directory.
 	 * @param accessLogDirectory access log directory
 	 */
-	void setAccessLogDirectory(File accessLogDirectory);
+	void setAccessLogDirectory(@Nullable File accessLogDirectory);
 
 	/**
 	 * Set the access log pattern.
 	 * @param accessLogPattern access log pattern
 	 */
-	void setAccessLogPattern(String accessLogPattern);
+	void setAccessLogPattern(@Nullable String accessLogPattern);
 
 	/**
 	 * Set the access log prefix.
 	 * @param accessLogPrefix log prefix
 	 */
-	void setAccessLogPrefix(String accessLogPrefix);
+	void setAccessLogPrefix(@Nullable String accessLogPrefix);
 
 	/**
 	 * Set the access log suffix.
 	 * @param accessLogSuffix access log suffix
 	 */
-	void setAccessLogSuffix(String accessLogSuffix);
+	void setAccessLogSuffix(@Nullable String accessLogSuffix);
 
 	/**
 	 * Set whether access logs are enabled.

module/spring-boot-undertow/src/main/java/org/springframework/boot/undertow/HttpHandlerFactory.java

@@ -20,6 +20,7 @@ import java.io.Closeable;
 
 import io.undertow.server.HttpHandler;
 import io.undertow.server.handlers.GracefulShutdownHandler;
+import org.jspecify.annotations.Nullable;
 
 import org.springframework.boot.undertow.servlet.UndertowServletWebServer;
 
@@ -43,6 +44,6 @@ public interface HttpHandlerFactory {
 	 * @param next the next handler in the chain
 	 * @return the new HTTP handler instance
 	 */
-	HttpHandler getHandler(HttpHandler next);
+	@Nullable HttpHandler getHandler(@Nullable HttpHandler next);
 
 }

module/spring-boot-undertow/src/main/java/org/springframework/boot/undertow/SslBuilderCustomizer.java

@@ -24,6 +24,7 @@ import javax.net.ssl.SSLContext;
 import io.undertow.Undertow;
 import io.undertow.protocols.ssl.SNIContextMatcher;
 import io.undertow.protocols.ssl.SNISSLContext;
+import org.jspecify.annotations.Nullable;
 import org.xnio.Options;
 import org.xnio.Sequence;
 import org.xnio.SslClientAuthMode;
@@ -44,15 +45,15 @@ class SslBuilderCustomizer implements UndertowBuilderCustomizer {
 
 	private final int port;
 
-	private final InetAddress address;
+	private final @Nullable InetAddress address;
 
-	private final ClientAuth clientAuth;
+	private final @Nullable ClientAuth clientAuth;
 
 	private final SslBundle sslBundle;
 
 	private final Map<String, SslBundle> serverNameSslBundles;
 
-	SslBuilderCustomizer(int port, InetAddress address, ClientAuth clientAuth, SslBundle sslBundle,
+	SslBuilderCustomizer(int port, @Nullable InetAddress address, @Nullable ClientAuth clientAuth, SslBundle sslBundle,
 			Map<String, SslBundle> serverNameSslBundles) {
 		this.port = port;
 		this.address = address;

module/spring-boot-undertow/src/main/java/org/springframework/boot/undertow/UndertowWebServer.java

@@ -32,6 +32,7 @@ import io.undertow.server.HttpServerExchange;
 import io.undertow.server.handlers.GracefulShutdownHandler;
 import org.apache.commons.logging.Log;
 import org.apache.commons.logging.LogFactory;
+import org.jspecify.annotations.Nullable;
 import org.xnio.channels.BoundChannel;
 
 import org.springframework.aot.hint.RuntimeHints;
@@ -61,7 +62,7 @@ public class UndertowWebServer implements WebServer {
 
 	private static final Log logger = LogFactory.getLog(UndertowWebServer.class);
 
-	private final AtomicReference<GracefulShutdownCallback> gracefulShutdownCallback = new AtomicReference<>();
+	private final AtomicReference<@Nullable GracefulShutdownCallback> gracefulShutdownCallback = new AtomicReference<>();
 
 	private final Object monitor = new Object();
 
@@ -71,13 +72,13 @@ public class UndertowWebServer implements WebServer {
 
 	private final boolean autoStart;
 
-	private Undertow undertow;
+	private @Nullable Undertow undertow;
 
 	private volatile boolean started = false;
 
-	private volatile GracefulShutdownHandler gracefulShutdown;
+	private volatile @Nullable GracefulShutdownHandler gracefulShutdown;
 
-	private volatile List<Closeable> closeables;
+	private volatile @Nullable List<Closeable> closeables;
 
 	/**
 	 * Create a new {@link UndertowWebServer} instance.
@@ -142,6 +143,7 @@ public class UndertowWebServer implements WebServer {
 		try {
 			if (this.undertow != null) {
 				this.undertow.stop();
+				Assert.state(this.closeables != null, "'closeables' must not be null");
 				this.closeables.forEach(this::closeSilently);
 			}
 		}
@@ -167,11 +169,12 @@ public class UndertowWebServer implements WebServer {
 		return this.builder.build();
 	}
 
-	protected HttpHandler createHttpHandler() {
+	protected @Nullable HttpHandler createHttpHandler() {
 		HttpHandler handler = null;
 		for (HttpHandlerFactory factory : this.httpHandlerFactories) {
 			handler = factory.getHandler(handler);
 			if (handler instanceof Closeable closeable) {
+				Assert.state(this.closeables != null, "'closeables' must not be null");
 				this.closeables.add(closeable);
 			}
 			if (handler instanceof GracefulShutdownHandler shutdownHandler) {
@@ -220,11 +223,14 @@ public class UndertowWebServer implements WebServer {
 	@SuppressWarnings("unchecked")
 	private List<BoundChannel> extractChannels() {
 		Field channelsField = ReflectionUtils.findField(Undertow.class, "channels");
+		Assert.state(channelsField != null, "'channelsField' must not be null");
 		ReflectionUtils.makeAccessible(channelsField);
-		return (List<BoundChannel>) ReflectionUtils.getField(channelsField, this.undertow);
+		List<BoundChannel> channels = (List<BoundChannel>) ReflectionUtils.getField(channelsField, this.undertow);
+		Assert.state(channels != null, "'channels' must not be null");
+		return channels;
 	}
 
-	private UndertowWebServer.Port getPortFromChannel(BoundChannel channel) {
+	private UndertowWebServer.@Nullable Port getPortFromChannel(BoundChannel channel) {
 		SocketAddress socketAddress = channel.getLocalAddress();
 		if (socketAddress instanceof InetSocketAddress inetSocketAddress) {
 			Field sslField = ReflectionUtils.findField(channel.getClass(), "ssl");
@@ -253,20 +259,37 @@ public class UndertowWebServer implements WebServer {
 	@SuppressWarnings("unchecked")
 	private List<Object> extractListeners() {
 		Field listenersField = ReflectionUtils.findField(Undertow.class, "listeners");
+		Assert.state(listenersField != null, "'listenersField' must not be null");
 		ReflectionUtils.makeAccessible(listenersField);
-		return (List<Object>) ReflectionUtils.getField(listenersField, this.undertow);
+		List<Object> listeners = (List<Object>) ReflectionUtils.getField(listenersField, this.undertow);
+		Assert.state(listeners != null, "'listeners' must not be null");
+		return listeners;
 	}
 
 	private UndertowWebServer.Port getPortFromListener(Object listener) {
 		Field typeField = ReflectionUtils.findField(listener.getClass(), "type");
-		ReflectionUtils.makeAccessible(typeField);
-		String protocol = ReflectionUtils.getField(typeField, listener).toString();
+		Assert.state(typeField != null, "'typeField' must not be null");
+		String protocol = getProtocol(listener, typeField);
 		Field portField = ReflectionUtils.findField(listener.getClass(), "port");
-		ReflectionUtils.makeAccessible(portField);
-		int port = (Integer) ReflectionUtils.getField(portField, listener);
+		Assert.state(portField != null, "'portField' must not be null");
+		int port = getPort(listener, portField);
 		return new UndertowWebServer.Port(port, protocol);
 	}
 
+	private static Integer getPort(Object listener, Field portField) {
+		ReflectionUtils.makeAccessible(portField);
+		Integer value = (Integer) ReflectionUtils.getField(portField, listener);
+		Assert.state(value != null, "'value' must not be null");
+		return value;
+	}
+
+	private String getProtocol(Object listener, Field typeField) {
+		ReflectionUtils.makeAccessible(typeField);
+		Object value = ReflectionUtils.getField(typeField, listener);
+		Assert.state(value != null, "'value' must not be null");
+		return value.toString();
+	}
+
 	@Override
 	public void stop() throws WebServerException {
 		synchronized (this.monitor) {
@@ -278,9 +301,12 @@ public class UndertowWebServer implements WebServer {
 				notifyGracefulCallback(false);
 			}
 			try {
-				this.undertow.stop();
-				for (Closeable closeable : this.closeables) {
-					closeable.close();
+				if (this.undertow != null) {
+					this.undertow.stop();
+					Assert.state(this.closeables != null, "'closeables' must not be null");
+					for (Closeable closeable : this.closeables) {
+						closeable.close();
+					}
 				}
 			}
 			catch (Exception ex) {
@@ -304,7 +330,7 @@ public class UndertowWebServer implements WebServer {
 	 * @return the Undertow server or {@code null} if the server hasn't been started yet
 	 * @since 4.0.0
 	 */
-	public Undertow getUndertow() {
+	public @Nullable Undertow getUndertow() {
 		return this.undertow;
 	}
 
@@ -396,27 +422,30 @@ public class UndertowWebServer implements WebServer {
 	 */
 	private static final class CloseableHttpHandlerFactory implements HttpHandlerFactory {
 
-		private final Closeable closeable;
+		private final @Nullable Closeable closeable;
 
-		private CloseableHttpHandlerFactory(Closeable closeable) {
+		private CloseableHttpHandlerFactory(@Nullable Closeable closeable) {
 			this.closeable = closeable;
 		}
 
 		@Override
-		public HttpHandler getHandler(HttpHandler next) {
-			if (this.closeable == null) {
+		public @Nullable HttpHandler getHandler(@Nullable HttpHandler next) {
+			Closeable closeable = this.closeable;
+			if (closeable == null) {
 				return next;
 			}
 			return new CloseableHttpHandler() {
 
 				@Override
 				public void handleRequest(HttpServerExchange exchange) throws Exception {
-					next.handleRequest(exchange);
+					if (next != null) {
+						next.handleRequest(exchange);
+					}
 				}
 
 				@Override
 				public void close() throws IOException {
-					CloseableHttpHandlerFactory.this.closeable.close();
+					closeable.close();
 				}
 
 			};
@@ -438,7 +467,7 @@ public class UndertowWebServer implements WebServer {
 	static class UndertowWebServerRuntimeHints implements RuntimeHintsRegistrar {
 
 		@Override
-		public void registerHints(RuntimeHints hints, ClassLoader classLoader) {
+		public void registerHints(RuntimeHints hints, @Nullable ClassLoader classLoader) {
 			hints.reflection()
 				.registerTypeIfPresent(classLoader, "io.undertow.Undertow",
 						(hint) -> hint.withField("listeners").withField("channels"));

module/spring-boot-undertow/src/main/java/org/springframework/boot/undertow/UndertowWebServerFactory.java

@@ -31,6 +31,7 @@ import io.undertow.Handlers;
 import io.undertow.Undertow;
 import io.undertow.Undertow.Builder;
 import io.undertow.UndertowOptions;
+import org.jspecify.annotations.Nullable;
 
 import org.springframework.boot.ssl.SslBundle;
 import org.springframework.boot.web.server.AbstractConfigurableWebServerFactory;
@@ -52,21 +53,21 @@ public abstract class UndertowWebServerFactory extends AbstractConfigurableWebSe
 
 	private Set<UndertowBuilderCustomizer> builderCustomizers = new LinkedHashSet<>();
 
-	private Integer bufferSize;
+	private @Nullable Integer bufferSize;
 
-	private Integer ioThreads;
+	private @Nullable Integer ioThreads;
 
-	private Integer workerThreads;
+	private @Nullable Integer workerThreads;
 
-	private Boolean directBuffers;
+	private @Nullable Boolean directBuffers;
 
-	private File accessLogDirectory;
+	private @Nullable File accessLogDirectory;
 
-	private String accessLogPattern;
+	private @Nullable String accessLogPattern;
 
-	private String accessLogPrefix;
+	private @Nullable String accessLogPrefix;
 
-	private String accessLogSuffix;
+	private @Nullable String accessLogSuffix;
 
 	private boolean accessLogEnabled;
 
@@ -98,46 +99,46 @@ public abstract class UndertowWebServerFactory extends AbstractConfigurableWebSe
 	}
 
 	@Override
-	public void setBufferSize(Integer bufferSize) {
+	public void setBufferSize(@Nullable Integer bufferSize) {
 		this.bufferSize = bufferSize;
 	}
 
 	@Override
-	public void setIoThreads(Integer ioThreads) {
+	public void setIoThreads(@Nullable Integer ioThreads) {
 		this.ioThreads = ioThreads;
 	}
 
 	@Override
-	public void setWorkerThreads(Integer workerThreads) {
+	public void setWorkerThreads(@Nullable Integer workerThreads) {
 		this.workerThreads = workerThreads;
 	}
 
 	@Override
-	public void setUseDirectBuffers(Boolean directBuffers) {
+	public void setUseDirectBuffers(@Nullable Boolean directBuffers) {
 		this.directBuffers = directBuffers;
 	}
 
 	@Override
-	public void setAccessLogDirectory(File accessLogDirectory) {
+	public void setAccessLogDirectory(@Nullable File accessLogDirectory) {
 		this.accessLogDirectory = accessLogDirectory;
 	}
 
 	@Override
-	public void setAccessLogPattern(String accessLogPattern) {
+	public void setAccessLogPattern(@Nullable String accessLogPattern) {
 		this.accessLogPattern = accessLogPattern;
 	}
 
 	@Override
-	public void setAccessLogPrefix(String accessLogPrefix) {
+	public void setAccessLogPrefix(@Nullable String accessLogPrefix) {
 		this.accessLogPrefix = accessLogPrefix;
 	}
 
-	public String getAccessLogPrefix() {
+	public @Nullable String getAccessLogPrefix() {
 		return this.accessLogPrefix;
 	}
 
 	@Override
-	public void setAccessLogSuffix(String accessLogSuffix) {
+	public void setAccessLogSuffix(@Nullable String accessLogSuffix) {
 		this.accessLogSuffix = accessLogSuffix;
 	}
 
@@ -207,14 +208,16 @@ public abstract class UndertowWebServerFactory extends AbstractConfigurableWebSe
 				this.useForwardHeaders, webServerFactory.getServerHeader(), webServerFactory.getShutdown(),
 				initialHttpHandlerFactories);
 		if (isAccessLogEnabled()) {
+			Assert.state(this.accessLogDirectory != null, "Access log directory is not set");
 			factories.add(new AccessLogHttpHandlerFactory(this.accessLogDirectory, this.accessLogPattern,
 					this.accessLogPrefix, this.accessLogSuffix, this.accessLogRotate));
 		}
 		return factories;
 	}
 
-	static List<HttpHandlerFactory> createHttpHandlerFactories(Compression compression, boolean useForwardHeaders,
-			String serverHeader, Shutdown shutdown, HttpHandlerFactory... initialHttpHandlerFactories) {
+	static List<HttpHandlerFactory> createHttpHandlerFactories(@Nullable Compression compression,
+			boolean useForwardHeaders, @Nullable String serverHeader, Shutdown shutdown,
+			HttpHandlerFactory... initialHttpHandlerFactories) {
 		List<HttpHandlerFactory> factories = new ArrayList<>(Arrays.asList(initialHttpHandlerFactories));
 		if (compression != null && compression.getEnabled()) {
 			factories.add(new CompressionHttpHandlerFactory(compression));

module/spring-boot-undertow/src/main/java/org/springframework/boot/undertow/autoconfigure/UndertowServerProperties.java

@@ -24,6 +24,7 @@ import java.util.LinkedHashMap;
 import java.util.Map;
 
 import io.undertow.UndertowOptions;
+import org.jspecify.annotations.Nullable;
 
 import org.springframework.boot.context.properties.ConfigurationProperties;
 import org.springframework.util.unit.DataSize;
@@ -69,13 +70,13 @@ public class UndertowServerProperties {
 	 * Size of each buffer. The default is derived from the maximum amount of memory that
 	 * is available to the JVM.
 	 */
-	private DataSize bufferSize;
+	private @Nullable DataSize bufferSize;
 
 	/**
 	 * Whether to allocate buffers outside the Java heap. The default is derived from the
 	 * maximum amount of memory that is available to the JVM.
 	 */
-	private Boolean directBuffers;
+	private @Nullable Boolean directBuffers;
 
 	/**
 	 * Whether servlet filters should be initialized on startup.
@@ -106,7 +107,7 @@ public class UndertowServerProperties {
 	 * enable this if you have a legacy application that requires it. When set,
 	 * server.undertow.allow-encoded-slash has no effect.
 	 */
-	private Boolean decodeSlash;
+	private @Nullable Boolean decodeSlash;
 
 	/**
 	 * Whether the URL should be decoded. When disabled, percent-encoded characters in the
@@ -129,7 +130,7 @@ public class UndertowServerProperties {
 	 * Amount of time a connection can sit idle without processing a request, before it is
 	 * closed by the server.
 	 */
-	private Duration noRequestTimeout;
+	private @Nullable Duration noRequestTimeout;
 
 	/**
 	 * Whether to preserve the path of a request when it is forwarded.
@@ -153,19 +154,19 @@ public class UndertowServerProperties {
 		this.maxHttpPostSize = maxHttpPostSize;
 	}
 
-	public DataSize getBufferSize() {
+	public @Nullable DataSize getBufferSize() {
 		return this.bufferSize;
 	}
 
-	public void setBufferSize(DataSize bufferSize) {
+	public void setBufferSize(@Nullable DataSize bufferSize) {
 		this.bufferSize = bufferSize;
 	}
 
-	public Boolean getDirectBuffers() {
+	public @Nullable Boolean getDirectBuffers() {
 		return this.directBuffers;
 	}
 
-	public void setDirectBuffers(Boolean directBuffers) {
+	public void setDirectBuffers(@Nullable Boolean directBuffers) {
 		this.directBuffers = directBuffers;
 	}
 
@@ -201,11 +202,11 @@ public class UndertowServerProperties {
 		this.maxCookies = maxCookies;
 	}
 
-	public Boolean getDecodeSlash() {
+	public @Nullable Boolean getDecodeSlash() {
 		return this.decodeSlash;
 	}
 
-	public void setDecodeSlash(Boolean decodeSlash) {
+	public void setDecodeSlash(@Nullable Boolean decodeSlash) {
 		this.decodeSlash = decodeSlash;
 	}
 
@@ -233,11 +234,11 @@ public class UndertowServerProperties {
 		this.alwaysSetKeepAlive = alwaysSetKeepAlive;
 	}
 
-	public Duration getNoRequestTimeout() {
+	public @Nullable Duration getNoRequestTimeout() {
 		return this.noRequestTimeout;
 	}
 
-	public void setNoRequestTimeout(Duration noRequestTimeout) {
+	public void setNoRequestTimeout(@Nullable Duration noRequestTimeout) {
 		this.noRequestTimeout = noRequestTimeout;
 	}
 
@@ -355,26 +356,26 @@ public class UndertowServerProperties {
 		 * Number of I/O threads to create for the worker. The default is derived from the
 		 * number of available processors.
 		 */
-		private Integer io;
+		private @Nullable Integer io;
 
 		/**
 		 * Number of worker threads. The default is 8 times the number of I/O threads.
 		 */
-		private Integer worker;
+		private @Nullable Integer worker;
 
-		public Integer getIo() {
+		public @Nullable Integer getIo() {
 			return this.io;
 		}
 
-		public void setIo(Integer io) {
+		public void setIo(@Nullable Integer io) {
 			this.io = io;
 		}
 
-		public Integer getWorker() {
+		public @Nullable Integer getWorker() {
 			return this.worker;
 		}
 
-		public void setWorker(Integer worker) {
+		public void setWorker(@Nullable Integer worker) {
 			this.worker = worker;
 		}
 

module/spring-boot-undertow/src/main/java/org/springframework/boot/undertow/autoconfigure/actuate/web/server/UndertowAccessLogCustomizer.java

@@ -18,6 +18,8 @@ package org.springframework.boot.undertow.autoconfigure.actuate.web.server;
 
 import java.util.function.Function;
 
+import org.jspecify.annotations.Nullable;
+
 import org.springframework.boot.actuate.autoconfigure.web.server.AccessLogCustomizer;
 import org.springframework.boot.undertow.ConfigurableUndertowWebServerFactory;
 
@@ -29,10 +31,10 @@ import org.springframework.boot.undertow.ConfigurableUndertowWebServerFactory;
  */
 class UndertowAccessLogCustomizer<T extends ConfigurableUndertowWebServerFactory> extends AccessLogCustomizer<T> {
 
-	private final Function<T, String> accessLogPrefixExtractor;
+	private final Function<T, @Nullable String> accessLogPrefixExtractor;
 
 	UndertowAccessLogCustomizer(UndertowManagementServerProperties properties,
-			Function<T, String> accessLogPrefixExtractor) {
+			Function<T, @Nullable String> accessLogPrefixExtractor) {
 		super(properties.getAccesslog().getPrefix());
 		this.accessLogPrefixExtractor = accessLogPrefixExtractor;
 	}

module/spring-boot-undertow/src/main/java/org/springframework/boot/undertow/autoconfigure/actuate/web/server/package-info.java

@@ -17,4 +17,7 @@
 /**
  * Actuator Undertow actuator web concerns.
  */
+@NullMarked
 package org.springframework.boot.undertow.autoconfigure.actuate.web.server;
+
+import org.jspecify.annotations.NullMarked;

module/spring-boot-undertow/src/main/java/org/springframework/boot/undertow/autoconfigure/package-info.java

@@ -18,4 +18,7 @@
  * Classes related to the auto-configuration of a servlet or reactive web server using
  * Undertow.
  */
+@NullMarked
 package org.springframework.boot.undertow.autoconfigure;
+
+import org.jspecify.annotations.NullMarked;

module/spring-boot-undertow/src/main/java/org/springframework/boot/undertow/autoconfigure/reactive/package-info.java

@@ -17,4 +17,7 @@
 /**
  * Classes related to the auto-configuration of a reactive web server using Undertow.
  */
+@NullMarked
 package org.springframework.boot.undertow.autoconfigure.reactive;
+
+import org.jspecify.annotations.NullMarked;

module/spring-boot-undertow/src/main/java/org/springframework/boot/undertow/autoconfigure/servlet/package-info.java

@@ -17,4 +17,7 @@
 /**
  * Classes related to the auto-configuration of a servlet web server using Undertow.
  */
+@NullMarked
 package org.springframework.boot.undertow.autoconfigure.servlet;
+
+import org.jspecify.annotations.NullMarked;

module/spring-boot-undertow/src/main/java/org/springframework/boot/undertow/package-info.java

@@ -20,4 +20,7 @@
  * @see org.springframework.boot.undertow.servlet.UndertowServletWebServerFactory
  * @see org.springframework.boot.undertow.reactive.UndertowReactiveWebServerFactory
  */
+@NullMarked
 package org.springframework.boot.undertow;
+
+import org.jspecify.annotations.NullMarked;

module/spring-boot-undertow/src/main/java/org/springframework/boot/undertow/reactive/package-info.java

@@ -17,4 +17,7 @@
 /**
  * Reactive web server implementation backed by Undertow.
  */
+@NullMarked
 package org.springframework.boot.undertow.reactive;
+
+import org.jspecify.annotations.NullMarked;

module/spring-boot-undertow/src/main/java/org/springframework/boot/undertow/servlet/CompositeResourceManager.java

@@ -24,6 +24,7 @@ import io.undertow.UndertowMessages;
 import io.undertow.server.handlers.resource.Resource;
 import io.undertow.server.handlers.resource.ResourceChangeListener;
 import io.undertow.server.handlers.resource.ResourceManager;
+import org.jspecify.annotations.Nullable;
 
 /**
  * A {@link ResourceManager} that delegates to multiple {@code ResourceManager} instances.
@@ -46,7 +47,7 @@ class CompositeResourceManager implements ResourceManager {
 	}
 
 	@Override
-	public Resource getResource(String path) throws IOException {
+	public @Nullable Resource getResource(String path) throws IOException {
 		for (ResourceManager resourceManager : this.resourceManagers) {
 			Resource resource = resourceManager.getResource(path);
 			if (resource != null) {

module/spring-boot-undertow/src/main/java/org/springframework/boot/undertow/servlet/DeploymentManagerHttpHandlerFactory.java

@@ -23,6 +23,7 @@ import io.undertow.server.HttpHandler;
 import io.undertow.server.HttpServerExchange;
 import io.undertow.servlet.api.DeploymentManager;
 import jakarta.servlet.ServletException;
+import org.jspecify.annotations.Nullable;
 
 import org.springframework.boot.undertow.HttpHandlerFactory;
 import org.springframework.util.Assert;
@@ -42,7 +43,7 @@ class DeploymentManagerHttpHandlerFactory implements HttpHandlerFactory {
 	}
 
 	@Override
-	public HttpHandler getHandler(HttpHandler next) {
+	public @Nullable HttpHandler getHandler(@Nullable HttpHandler next) {
 		Assert.state(next == null, "DeploymentManagerHttpHandlerFactory must be first");
 		return new DeploymentManagerHandler(this.deploymentManager);
 	}

module/spring-boot-undertow/src/main/java/org/springframework/boot/undertow/servlet/FileSessionPersistence.java

@@ -29,6 +29,7 @@ import java.util.Map;
 
 import io.undertow.servlet.UndertowServletLogger;
 import io.undertow.servlet.api.SessionPersistenceManager;
+import org.jspecify.annotations.Nullable;
 
 import org.springframework.core.ConfigurableObjectInputStream;
 
@@ -70,7 +71,8 @@ class FileSessionPersistence implements SessionPersistenceManager {
 	}
 
 	@Override
-	public Map<String, PersistentSession> loadSessionAttributes(String deploymentName, final ClassLoader classLoader) {
+	public @Nullable Map<String, PersistentSession> loadSessionAttributes(String deploymentName,
+			final ClassLoader classLoader) {
 		try {
 			File file = getSessionFile(deploymentName);
 			if (file.exists()) {

module/spring-boot-undertow/src/main/java/org/springframework/boot/undertow/servlet/JarResourceManager.java

@@ -26,6 +26,7 @@ import io.undertow.server.handlers.resource.Resource;
 import io.undertow.server.handlers.resource.ResourceChangeListener;
 import io.undertow.server.handlers.resource.ResourceManager;
 import io.undertow.server.handlers.resource.URLResource;
+import org.jspecify.annotations.Nullable;
 
 import org.springframework.util.StringUtils;
 
@@ -49,7 +50,7 @@ class JarResourceManager implements ResourceManager {
 	}
 
 	@Override
-	public Resource getResource(String path) throws IOException {
+	public @Nullable Resource getResource(String path) throws IOException {
 		URL url = new URL("jar:" + this.jarPath + "!" + (path.startsWith("/") ? path : "/" + path));
 		URLResource resource = new URLResource(url, path);
 		if (StringUtils.hasText(path) && !"/".equals(path) && resource.getContentLength() < 0) {

module/spring-boot-undertow/src/main/java/org/springframework/boot/undertow/servlet/UndertowServletWebServer.java

@@ -20,6 +20,7 @@ import io.undertow.Handlers;
 import io.undertow.Undertow.Builder;
 import io.undertow.server.HttpHandler;
 import io.undertow.servlet.api.DeploymentManager;
+import org.jspecify.annotations.Nullable;
 
 import org.springframework.boot.undertow.HttpHandlerFactory;
 import org.springframework.boot.undertow.UndertowWebServer;
@@ -43,7 +44,7 @@ public class UndertowServletWebServer extends UndertowWebServer {
 
 	private final String contextPath;
 
-	private final DeploymentManager manager;
+	private final @Nullable DeploymentManager manager;
 
 	/**
 	 * Create a new {@link UndertowServletWebServer} instance.
@@ -60,7 +61,7 @@ public class UndertowServletWebServer extends UndertowWebServer {
 		this.manager = findManager(httpHandlerFactories);
 	}
 
-	private DeploymentManager findManager(Iterable<HttpHandlerFactory> httpHandlerFactories) {
+	private @Nullable DeploymentManager findManager(Iterable<HttpHandlerFactory> httpHandlerFactories) {
 		for (HttpHandlerFactory httpHandlerFactory : httpHandlerFactories) {
 			if (httpHandlerFactory instanceof DeploymentManagerHttpHandlerFactory deploymentManagerFactory) {
 				return deploymentManagerFactory.getDeploymentManager();
@@ -70,7 +71,7 @@ public class UndertowServletWebServer extends UndertowWebServer {
 	}
 
 	@Override
-	protected HttpHandler createHttpHandler() {
+	protected @Nullable HttpHandler createHttpHandler() {
 		HttpHandler handler = super.createHttpHandler();
 		if (StringUtils.hasLength(this.contextPath)) {
 			handler = Handlers.path().addPrefixPath(this.contextPath, handler);
@@ -88,7 +89,7 @@ public class UndertowServletWebServer extends UndertowWebServer {
 		return message.toString();
 	}
 
-	public DeploymentManager getDeploymentManager() {
+	public @Nullable DeploymentManager getDeploymentManager() {
 		return this.manager;
 	}
 

module/spring-boot-undertow/src/main/java/org/springframework/boot/undertow/servlet/UndertowServletWebServerFactory.java

@@ -61,6 +61,7 @@ import jakarta.servlet.ServletContext;
 import jakarta.servlet.ServletException;
 import org.apache.commons.logging.Log;
 import org.apache.commons.logging.LogFactory;
+import org.jspecify.annotations.Nullable;
 
 import org.springframework.boot.context.properties.PropertyMapper;
 import org.springframework.boot.undertow.HttpHandlerFactory;
@@ -110,6 +111,7 @@ public class UndertowServletWebServerFactory extends UndertowWebServerFactory
 
 	private Set<UndertowDeploymentInfoCustomizer> deploymentInfoCustomizers = new LinkedHashSet<>();
 
+	@SuppressWarnings("NullAway.Init")
 	private ResourceLoader resourceLoader;
 
 	private boolean eagerFilterInit = true;
@@ -273,10 +275,12 @@ public class UndertowServletWebServerFactory extends UndertowWebServerFactory
 
 	@SuppressWarnings("unchecked")
 	private Class<? extends EventListener> loadWebListenerClass(String className) throws ClassNotFoundException {
-		return (Class<? extends EventListener>) getServletClassLoader().loadClass(className);
+		ClassLoader classLoader = getServletClassLoader();
+		Assert.state(classLoader != null, "'classLoader' must not be null");
+		return (Class<? extends EventListener>) classLoader.loadClass(className);
 	}
 
-	private boolean isZeroOrLess(Duration timeoutDuration) {
+	private boolean isZeroOrLess(@Nullable Duration timeoutDuration) {
 		return timeoutDuration == null || timeoutDuration.isZero() || timeoutDuration.isNegative();
 	}
 
@@ -293,7 +297,7 @@ public class UndertowServletWebServerFactory extends UndertowWebServerFactory
 				new ImmediateInstanceFactory<>(initializer), NO_CLASSES));
 	}
 
-	private ClassLoader getServletClassLoader() {
+	private @Nullable ClassLoader getServletClassLoader() {
 		if (this.resourceLoader != null) {
 			return this.resourceLoader.getClassLoader();
 		}
@@ -337,7 +341,7 @@ public class UndertowServletWebServerFactory extends UndertowWebServerFactory
 		return new CompositeResourceManager(managers.toArray(new ResourceManager[0]));
 	}
 
-	private File getCanonicalDocumentRoot(File docBase) {
+	private File getCanonicalDocumentRoot(@Nullable File docBase) {
 		try {
 			File root = (docBase != null) ? docBase : createTempDir("undertow-docbase");
 			return root.getCanonicalFile();
@@ -402,7 +406,7 @@ public class UndertowServletWebServerFactory extends UndertowWebServerFactory
 				port >= 0);
 	}
 
-	private HttpHandlerFactory getCookieHandlerFactory(Deployment deployment) {
+	private @Nullable HttpHandlerFactory getCookieHandlerFactory(Deployment deployment) {
 		SameSite sessionSameSite = getSettings().getSession().getCookie().getSameSite();
 		List<CookieSameSiteSupplier> suppliers = new ArrayList<>();
 		if (sessionSameSite != null) {
@@ -458,7 +462,7 @@ public class UndertowServletWebServerFactory extends UndertowWebServerFactory
 		}
 
 		@Override
-		public Resource getResource(String path) {
+		public @Nullable Resource getResource(String path) {
 			for (URL url : this.metaInfResourceJarUrls) {
 				URLResource resource = getMetaInfResource(url, path);
 				if (resource != null) {
@@ -482,7 +486,7 @@ public class UndertowServletWebServerFactory extends UndertowWebServerFactory
 
 		}
 
-		private URLResource getMetaInfResource(URL resourceJar, String path) {
+		private @Nullable URLResource getMetaInfResource(URL resourceJar, String path) {
 			try {
 				String urlPath = URLEncoder.encode(ENCODED_SLASH.matcher(path).replaceAll("/"), StandardCharsets.UTF_8);
 				URL resourceUrl = new URL(resourceJar + "META-INF/resources" + urlPath);
@@ -511,7 +515,7 @@ public class UndertowServletWebServerFactory extends UndertowWebServerFactory
 		}
 
 		@Override
-		public Resource getResource(String path) throws IOException {
+		public @Nullable Resource getResource(String path) throws IOException {
 			if (path.startsWith("/org/springframework/boot")) {
 				return null;
 			}
@@ -546,11 +550,11 @@ public class UndertowServletWebServerFactory extends UndertowWebServerFactory
 	 */
 	private static class SuppliedSameSiteCookieHandler implements HttpHandler {
 
-		private final HttpHandler next;
+		private final @Nullable HttpHandler next;
 
 		private final List<CookieSameSiteSupplier> suppliers;
 
-		SuppliedSameSiteCookieHandler(HttpHandler next, List<CookieSameSiteSupplier> suppliers) {
+		SuppliedSameSiteCookieHandler(@Nullable HttpHandler next, List<CookieSameSiteSupplier> suppliers) {
 			this.next = next;
 			this.suppliers = suppliers;
 		}
@@ -558,7 +562,9 @@ public class UndertowServletWebServerFactory extends UndertowWebServerFactory
 		@Override
 		public void handleRequest(HttpServerExchange exchange) throws Exception {
 			exchange.addResponseCommitListener(this::beforeCommit);
-			this.next.handleRequest(exchange);
+			if (this.next != null) {
+				this.next.handleRequest(exchange);
+			}
 		}
 
 		private void beforeCommit(HttpServerExchange exchange) {
@@ -587,7 +593,7 @@ public class UndertowServletWebServerFactory extends UndertowWebServerFactory
 			return result;
 		}
 
-		private SameSite getSameSite(jakarta.servlet.http.Cookie cookie) {
+		private @Nullable SameSite getSameSite(jakarta.servlet.http.Cookie cookie) {
 			for (CookieSameSiteSupplier supplier : this.suppliers) {
 				SameSite sameSite = supplier.getSameSite(cookie);
 				if (sameSite != null) {

module/spring-boot-undertow/src/main/java/org/springframework/boot/undertow/servlet/package-info.java

@@ -17,4 +17,7 @@
 /**
  * Servlet web server implementation backed by Undertow.
  */
+@NullMarked
 package org.springframework.boot.undertow.servlet;
+
+import org.jspecify.annotations.NullMarked;