Add nullability annotations to loader/spring-boot-loader-tools

See gh-46587

documentation/spring-boot-docs/src/main/kotlin/org/springframework/boot/docs/buildtoolplugins/otherbuildsystems/examplerepackageimplementation/MyBuildTool.kt

@@ -27,7 +27,7 @@ class MyBuildTool {
 
 	@Throws(IOException::class)
 	fun build() {
-		val sourceJarFile: File? =  /**/null
+		val sourceJarFile: File =  /**/File(".")
 		val repackager = Repackager(sourceJarFile)
 		repackager.setBackupSource(false)
 		repackager.repackage { callback: LibraryCallback -> getLibraries(callback) }
@@ -36,14 +36,14 @@ class MyBuildTool {
 	@Throws(IOException::class)
 	private fun getLibraries(callback: LibraryCallback) {
 		// Build system specific implementation, callback for each dependency
-		for (nestedJar in getCompileScopeJars()!!) {
+		for (nestedJar in getCompileScopeJars()) {
 			callback.library(Library(nestedJar, LibraryScope.COMPILE))
 		}
 		// ...
 	}
 
-	private fun getCompileScopeJars(): List<File?>? {
-		return  /**/ null
+	private fun getCompileScopeJars(): List<File> {
+		return  /**/ listOf()
 	}
 
 }

loader/spring-boot-loader-tools/src/main/java/org/springframework/boot/loader/tools/AbstractJarWriter.java

@@ -42,6 +42,9 @@ import java.util.zip.ZipEntry;
 import org.apache.commons.compress.archivers.jar.JarArchiveEntry;
 import org.apache.commons.compress.archivers.zip.UnixStat;
 import org.apache.commons.compress.archivers.zip.ZipArchiveEntry;
+import org.jspecify.annotations.Nullable;
+
+import org.springframework.util.Assert;
 
 /**
  * Abstract base class for JAR writers.
@@ -61,16 +64,16 @@ public abstract class AbstractJarWriter implements LoaderClassesWriter {
 
 	private final Set<String> writtenEntries = new HashSet<>();
 
-	private Layers layers;
+	private @Nullable Layers layers;
 
-	private LayersIndex layersIndex;
+	private @Nullable LayersIndex layersIndex;
 
 	/**
 	 * Update this writer to use specific layers.
 	 * @param layers the layers to use
 	 * @param layersIndex the layers index to update
 	 */
-	void useLayers(Layers layers, LayersIndex layersIndex) {
+	void useLayers(@Nullable Layers layers, @Nullable LayersIndex layersIndex) {
 		this.layers = layers;
 		this.layersIndex = layersIndex;
 	}
@@ -86,7 +89,7 @@ public abstract class AbstractJarWriter implements LoaderClassesWriter {
 	}
 
 	final void writeEntries(JarFile jarFile, EntryTransformer entryTransformer, UnpackHandler unpackHandler,
-			Function<JarEntry, Library> libraryLookup) throws IOException {
+			Function<JarEntry, @Nullable Library> libraryLookup) throws IOException {
 		Enumeration<JarEntry> entries = jarFile.entries();
 		while (entries.hasMoreElements()) {
 			JarEntry entry = entries.nextElement();
@@ -98,7 +101,7 @@ public abstract class AbstractJarWriter implements LoaderClassesWriter {
 	}
 
 	private void writeEntry(JarFile jarFile, EntryTransformer entryTransformer, UnpackHandler unpackHandler,
-			JarArchiveEntry entry, Library library) throws IOException {
+			JarArchiveEntry entry, @Nullable Library library) throws IOException {
 		setUpEntry(jarFile, entry, unpackHandler);
 		try (ZipHeaderPeekInputStream inputStream = new ZipHeaderPeekInputStream(jarFile.getInputStream(entry))) {
 			EntryWriter entryWriter = new InputStreamEntryWriter(inputStream);
@@ -168,7 +171,7 @@ public abstract class AbstractJarWriter implements LoaderClassesWriter {
 	 * @throws IOException if the write fails
 	 * @since 2.3.0
 	 */
-	public void writeIndexFile(String location, Collection<String> lines) throws IOException {
+	public void writeIndexFile(@Nullable String location, Collection<String> lines) throws IOException {
 		if (location != null) {
 			JarArchiveEntry entry = new JarArchiveEntry(location);
 			writeEntry(entry, (outputStream) -> {
@@ -207,7 +210,7 @@ public abstract class AbstractJarWriter implements LoaderClassesWriter {
 	}
 
 	@Override
-	public void writeLoaderClasses(LoaderImplementation loaderImplementation) throws IOException {
+	public void writeLoaderClasses(@Nullable LoaderImplementation loaderImplementation) throws IOException {
 		writeLoaderClasses((loaderImplementation != null) ? loaderImplementation.getJarResourceName()
 				: LoaderImplementation.DEFAULT.getJarResourceName());
 	}
@@ -255,7 +258,8 @@ public abstract class AbstractJarWriter implements LoaderClassesWriter {
 	 * @param entryWriter the entry writer or {@code null} if there is no content
 	 * @throws IOException in case of I/O errors
 	 */
-	private void writeEntry(JarArchiveEntry entry, Library library, EntryWriter entryWriter) throws IOException {
+	private void writeEntry(JarArchiveEntry entry, @Nullable Library library, @Nullable EntryWriter entryWriter)
+			throws IOException {
 		String name = entry.getName();
 		if (this.writtenEntries.add(name)) {
 			writeParentDirectoryEntries(name);
@@ -263,6 +267,7 @@ public abstract class AbstractJarWriter implements LoaderClassesWriter {
 			entry.getGeneralPurposeBit().useUTF8ForNames(true);
 			if (!entry.isDirectory() && entry.getSize() == -1) {
 				entryWriter = SizeCalculatingEntryWriter.get(entryWriter);
+				Assert.state(entryWriter != null, "'entryWriter' must not be null");
 				entry.setSize(entryWriter.size());
 			}
 			updateLayerIndex(entry, library);
@@ -270,14 +275,14 @@ public abstract class AbstractJarWriter implements LoaderClassesWriter {
 		}
 	}
 
-	private void updateLayerIndex(JarArchiveEntry entry, Library library) {
-		if (this.layers != null && !entry.getName().endsWith("/")) {
+	private void updateLayerIndex(JarArchiveEntry entry, @Nullable Library library) {
+		if (this.layers != null && this.layersIndex != null && !entry.getName().endsWith("/")) {
 			Layer layer = (library != null) ? this.layers.getLayer(library) : this.layers.getLayer(entry.getName());
 			this.layersIndex.add(layer, entry.getName());
 		}
 	}
 
-	protected abstract void writeToArchive(ZipEntry entry, EntryWriter entryWriter) throws IOException;
+	protected abstract void writeToArchive(ZipEntry entry, @Nullable EntryWriter entryWriter) throws IOException;
 
 	private void writeParentDirectoryEntries(String name) throws IOException {
 		String parent = name.endsWith("/") ? name.substring(0, name.length() - 1) : name;
@@ -320,7 +325,7 @@ public abstract class AbstractJarWriter implements LoaderClassesWriter {
 
 		private static final int BUFFER_SIZE = 32 * 1024;
 
-		private final MessageDigest messageDigest;
+		private final @Nullable MessageDigest messageDigest;
 
 		private final CRC32 crc = new CRC32();
 
@@ -378,7 +383,7 @@ public abstract class AbstractJarWriter implements LoaderClassesWriter {
 		 */
 		EntryTransformer NONE = (jarEntry) -> jarEntry;
 
-		JarArchiveEntry transform(JarArchiveEntry jarEntry);
+		@Nullable JarArchiveEntry transform(JarArchiveEntry jarEntry);
 
 	}
 

loader/spring-boot-loader-tools/src/main/java/org/springframework/boot/loader/tools/BuildPropertiesWriter.java

@@ -24,6 +24,8 @@ import java.time.format.DateTimeFormatter;
 import java.util.Map;
 import java.util.Properties;
 
+import org.jspecify.annotations.Nullable;
+
 import org.springframework.core.CollectionFactory;
 import org.springframework.util.StringUtils;
 
@@ -86,7 +88,7 @@ public final class BuildPropertiesWriter {
 		return properties;
 	}
 
-	private void addIfHasValue(Properties properties, String name, String value) {
+	private void addIfHasValue(Properties properties, String name, @Nullable String value) {
 		if (StringUtils.hasText(value)) {
 			properties.put(name, value);
 		}
@@ -97,20 +99,20 @@ public final class BuildPropertiesWriter {
 	 */
 	public static final class ProjectDetails {
 
-		private final String group;
+		private final @Nullable String group;
 
-		private final String artifact;
+		private final @Nullable String artifact;
 
-		private final String name;
+		private final @Nullable String name;
 
-		private final String version;
+		private final @Nullable String version;
 
-		private final Instant time;
+		private final @Nullable Instant time;
 
-		private final Map<String, String> additionalProperties;
+		private final @Nullable Map<String, String> additionalProperties;
 
-		public ProjectDetails(String group, String artifact, String version, String name, Instant time,
-				Map<String, String> additionalProperties) {
+		public ProjectDetails(@Nullable String group, @Nullable String artifact, @Nullable String version,
+				@Nullable String name, @Nullable Instant time, @Nullable Map<String, String> additionalProperties) {
 			this.group = group;
 			this.artifact = artifact;
 			this.name = name;
@@ -120,7 +122,7 @@ public final class BuildPropertiesWriter {
 			this.additionalProperties = additionalProperties;
 		}
 
-		private static void validateAdditionalProperties(Map<String, String> additionalProperties) {
+		private static void validateAdditionalProperties(@Nullable Map<String, String> additionalProperties) {
 			if (additionalProperties != null) {
 				additionalProperties.forEach((name, value) -> {
 					if (value == null) {
@@ -130,27 +132,27 @@ public final class BuildPropertiesWriter {
 			}
 		}
 
-		public String getGroup() {
+		public @Nullable String getGroup() {
 			return this.group;
 		}
 
-		public String getArtifact() {
+		public @Nullable String getArtifact() {
 			return this.artifact;
 		}
 
-		public String getName() {
+		public @Nullable String getName() {
 			return this.name;
 		}
 
-		public String getVersion() {
+		public @Nullable String getVersion() {
 			return this.version;
 		}
 
-		public Instant getTime() {
+		public @Nullable Instant getTime() {
 			return this.time;
 		}
 
-		public Map<String, String> getAdditionalProperties() {
+		public @Nullable Map<String, String> getAdditionalProperties() {
 			return this.additionalProperties;
 		}
 

loader/spring-boot-loader-tools/src/main/java/org/springframework/boot/loader/tools/DefaultLaunchScript.java

@@ -29,6 +29,8 @@ import java.util.Set;
 import java.util.regex.Matcher;
 import java.util.regex.Pattern;
 
+import org.jspecify.annotations.Nullable;
+
 /**
  * Default implementation of {@link LaunchScript}. Provides the default Spring Boot launch
  * script or can load a specific script File. Also support mustache style template
@@ -54,12 +56,12 @@ public class DefaultLaunchScript implements LaunchScript {
 	 * @param properties an optional set of script properties used for variable expansion
 	 * @throws IOException if the script cannot be loaded
 	 */
-	public DefaultLaunchScript(File file, Map<?, ?> properties) throws IOException {
+	public DefaultLaunchScript(@Nullable File file, Map<?, ?> properties) throws IOException {
 		String content = loadContent(file);
 		this.content = expandPlaceholders(content, properties);
 	}
 
-	private String loadContent(File file) throws IOException {
+	private String loadContent(@Nullable File file) throws IOException {
 		if (file == null) {
 			return loadContent(getClass().getResourceAsStream("launch.script"));
 		}
@@ -83,7 +85,7 @@ public class DefaultLaunchScript implements LaunchScript {
 		outputStream.flush();
 	}
 
-	private String expandPlaceholders(String content, Map<?, ?> properties) throws IOException {
+	private String expandPlaceholders(@Nullable String content, Map<?, ?> properties) throws IOException {
 		StringBuilder expanded = new StringBuilder();
 		Matcher matcher = PLACEHOLDER_PATTERN.matcher(content);
 		while (matcher.find()) {

loader/spring-boot-loader-tools/src/main/java/org/springframework/boot/loader/tools/FileUtils.java

@@ -23,6 +23,8 @@ import java.util.jar.Attributes;
 import java.util.jar.JarFile;
 import java.util.jar.Manifest;
 
+import org.jspecify.annotations.Nullable;
+
 /**
  * Utilities for manipulating files and directories in Spring Boot tooling.
  *
@@ -61,7 +63,10 @@ public abstract class FileUtils {
 	 * @return if the file has been signed
 	 * @throws IOException on IO error
 	 */
-	public static boolean isSignedJarFile(File file) throws IOException {
+	public static boolean isSignedJarFile(@Nullable File file) throws IOException {
+		if (file == null) {
+			return false;
+		}
 		try (JarFile jarFile = new JarFile(file)) {
 			if (hasDigestEntry(jarFile.getManifest())) {
 				return true;
@@ -70,7 +75,7 @@ public abstract class FileUtils {
 		return false;
 	}
 
-	private static boolean hasDigestEntry(Manifest manifest) {
+	private static boolean hasDigestEntry(@Nullable Manifest manifest) {
 		return (manifest != null) && manifest.getEntries().values().stream().anyMatch(FileUtils::hasDigestName);
 	}
 

loader/spring-boot-loader-tools/src/main/java/org/springframework/boot/loader/tools/ImagePackager.java

@@ -22,6 +22,8 @@ import java.util.function.BiConsumer;
 import java.util.jar.JarFile;
 import java.util.zip.ZipEntry;
 
+import org.jspecify.annotations.Nullable;
+
 import org.springframework.util.Assert;
 
 /**
@@ -38,7 +40,7 @@ public class ImagePackager extends Packager {
 	 * @param source the source file to package
 	 * @param backupFile the backup of the source file to package
 	 */
-	public ImagePackager(File source, File backupFile) {
+	public ImagePackager(File source, @Nullable File backupFile) {
 		super(source);
 		setBackupFile(backupFile);
 		if (isAlreadyPackaged()) {
@@ -55,7 +57,8 @@ public class ImagePackager extends Packager {
 	 * @param exporter the exporter used to write the image
 	 * @throws IOException on IO error
 	 */
-	public void packageImage(Libraries libraries, BiConsumer<ZipEntry, EntryWriter> exporter) throws IOException {
+	public void packageImage(Libraries libraries, BiConsumer<ZipEntry, @Nullable EntryWriter> exporter)
+			throws IOException {
 		packageImage(libraries, new DelegatingJarWriter(exporter));
 	}
 
@@ -71,14 +74,14 @@ public class ImagePackager extends Packager {
 	 */
 	private static class DelegatingJarWriter extends AbstractJarWriter {
 
-		private final BiConsumer<ZipEntry, EntryWriter> exporter;
+		private final BiConsumer<ZipEntry, @Nullable EntryWriter> exporter;
 
-		DelegatingJarWriter(BiConsumer<ZipEntry, EntryWriter> exporter) {
+		DelegatingJarWriter(BiConsumer<ZipEntry, @Nullable EntryWriter> exporter) {
 			this.exporter = exporter;
 		}
 
 		@Override
-		protected void writeToArchive(ZipEntry entry, EntryWriter entryWriter) throws IOException {
+		protected void writeToArchive(ZipEntry entry, @Nullable EntryWriter entryWriter) throws IOException {
 			this.exporter.accept(entry, entryWriter);
 		}
 

loader/spring-boot-loader-tools/src/main/java/org/springframework/boot/loader/tools/JarModeLibrary.java

@@ -63,7 +63,9 @@ public class JarModeLibrary extends Library {
 
 	@Override
 	public InputStream openStream() throws IOException {
-		String path = "META-INF/jarmode/" + getCoordinates().getArtifactId() + ".jar";
+		LibraryCoordinates coordinates = getCoordinates();
+		Assert.state(coordinates != null, "'coordinates' must not be null");
+		String path = "META-INF/jarmode/" + coordinates.getArtifactId() + ".jar";
 		URL resource = getClass().getClassLoader().getResource(path);
 		Assert.state(resource != null, () -> "Unable to find resource " + path);
 		return resource.openStream();

loader/spring-boot-loader-tools/src/main/java/org/springframework/boot/loader/tools/JarWriter.java

@@ -26,6 +26,7 @@ import java.util.zip.ZipException;
 
 import org.apache.commons.compress.archivers.jar.JarArchiveEntry;
 import org.apache.commons.compress.archivers.jar.JarArchiveOutputStream;
+import org.jspecify.annotations.Nullable;
 
 /**
  * Writes JAR content, ensuring valid directory entries are always created and duplicate
@@ -41,7 +42,7 @@ public class JarWriter extends AbstractJarWriter implements AutoCloseable {
 
 	private final JarArchiveOutputStream jarOutputStream;
 
-	private final FileTime lastModifiedTime;
+	private final @Nullable FileTime lastModifiedTime;
 
 	/**
 	 * Create a new {@link JarWriter} instance.
@@ -60,7 +61,7 @@ public class JarWriter extends AbstractJarWriter implements AutoCloseable {
 	 * @throws IOException if the file cannot be opened
 	 * @throws FileNotFoundException if the file cannot be found
 	 */
-	public JarWriter(File file, LaunchScript launchScript) throws FileNotFoundException, IOException {
+	public JarWriter(File file, @Nullable LaunchScript launchScript) throws FileNotFoundException, IOException {
 		this(file, launchScript, null);
 	}
 
@@ -74,7 +75,7 @@ public class JarWriter extends AbstractJarWriter implements AutoCloseable {
 	 * @throws FileNotFoundException if the file cannot be found
 	 * @since 2.3.0
 	 */
-	public JarWriter(File file, LaunchScript launchScript, FileTime lastModifiedTime)
+	public JarWriter(File file, @Nullable LaunchScript launchScript, @Nullable FileTime lastModifiedTime)
 			throws FileNotFoundException, IOException {
 		this.jarOutputStream = new JarArchiveOutputStream(new FileOutputStream(file));
 		if (launchScript != null) {
@@ -86,7 +87,7 @@ public class JarWriter extends AbstractJarWriter implements AutoCloseable {
 	}
 
 	@Override
-	protected void writeToArchive(ZipEntry entry, EntryWriter entryWriter) throws IOException {
+	protected void writeToArchive(ZipEntry entry, @Nullable EntryWriter entryWriter) throws IOException {
 		JarArchiveEntry jarEntry = asJarArchiveEntry(entry);
 		if (this.lastModifiedTime != null) {
 			jarEntry.setTime(DefaultTimeZoneOffset.INSTANCE.removeFrom(this.lastModifiedTime).toMillis());

loader/spring-boot-loader-tools/src/main/java/org/springframework/boot/loader/tools/Layer.java

@@ -19,6 +19,8 @@ package org.springframework.boot.loader.tools;
 import java.util.Locale;
 import java.util.regex.Pattern;
 
+import org.jspecify.annotations.Nullable;
+
 import org.springframework.util.Assert;
 
 /**
@@ -48,7 +50,7 @@ public class Layer {
 	}
 
 	@Override
-	public boolean equals(Object obj) {
+	public boolean equals(@Nullable Object obj) {
 		if (this == obj) {
 			return true;
 		}

loader/spring-boot-loader-tools/src/main/java/org/springframework/boot/loader/tools/Layout.java

@@ -16,6 +16,8 @@
 
 package org.springframework.boot.loader.tools;
 
+import org.jspecify.annotations.Nullable;
+
 /**
  * Strategy interface used to determine the layout for a particular type of archive.
  * Layouts may additionally implement {@link CustomLoaderLayout} if they wish to write
@@ -33,7 +35,7 @@ public interface Layout {
 	 * Returns the launcher class name for this layout.
 	 * @return the launcher class name
 	 */
-	String getLauncherClassName();
+	@Nullable String getLauncherClassName();
 
 	/**
 	 * Returns the destination path for a given library.
@@ -42,7 +44,7 @@ public interface Layout {
 	 * @return the location of the library relative to the root of the archive (should end
 	 * with '/') or {@code null} if the library should not be included.
 	 */
-	String getLibraryLocation(String libraryName, LibraryScope scope);
+	@Nullable String getLibraryLocation(String libraryName, @Nullable LibraryScope scope);
 
 	/**
 	 * Returns the location of classes within the archive.
@@ -57,7 +59,7 @@ public interface Layout {
 	 * @return the classpath index file location
 	 * @since 2.5.0
 	 */
-	default String getClasspathIndexFileLocation() {
+	default @Nullable String getClasspathIndexFileLocation() {
 		return null;
 	}
 
@@ -68,7 +70,7 @@ public interface Layout {
 	 * @return the layer index file location
 	 * @since 2.5.0
 	 */
-	default String getLayersIndexFileLocation() {
+	default @Nullable String getLayersIndexFileLocation() {
 		return null;
 	}
 

loader/spring-boot-loader-tools/src/main/java/org/springframework/boot/loader/tools/Layouts.java

@@ -22,6 +22,10 @@ import java.util.HashMap;
 import java.util.Locale;
 import java.util.Map;
 
+import org.jspecify.annotations.Nullable;
+
+import org.springframework.util.Assert;
+
 /**
  * Common {@link Layout layouts}.
  *
@@ -43,9 +47,7 @@ public final class Layouts {
 	 * @return a {@link Layout}
 	 */
 	public static Layout forFile(File file) {
-		if (file == null) {
-			throw new IllegalArgumentException("File must not be null");
-		}
+		Assert.notNull(file, "'file' must not be null");
 		String lowerCaseFileName = file.getName().toLowerCase(Locale.ENGLISH);
 		if (lowerCaseFileName.endsWith(".jar")) {
 			return new Jar();
@@ -65,12 +67,12 @@ public final class Layouts {
 	public static class Jar implements RepackagingLayout {
 
 		@Override
-		public String getLauncherClassName() {
+		public @Nullable String getLauncherClassName() {
 			return "org.springframework.boot.loader.launch.JarLauncher";
 		}
 
 		@Override
-		public String getLibraryLocation(String libraryName, LibraryScope scope) {
+		public String getLibraryLocation(String libraryName, @Nullable LibraryScope scope) {
 			return "BOOT-INF/lib/";
 		}
 
@@ -119,7 +121,7 @@ public final class Layouts {
 	public static class None extends Jar {
 
 		@Override
-		public String getLauncherClassName() {
+		public @Nullable String getLauncherClassName() {
 			return null;
 		}
 
@@ -152,7 +154,7 @@ public final class Layouts {
 		}
 
 		@Override
-		public String getLibraryLocation(String libraryName, LibraryScope scope) {
+		public @Nullable String getLibraryLocation(String libraryName, @Nullable LibraryScope scope) {
 			return SCOPE_LOCATION.get(scope);
 		}
 

loader/spring-boot-loader-tools/src/main/java/org/springframework/boot/loader/tools/Library.java

@@ -21,6 +21,10 @@ import java.io.FileInputStream;
 import java.io.IOException;
 import java.io.InputStream;
 
+import org.jspecify.annotations.Nullable;
+
+import org.springframework.util.Assert;
+
 /**
  * Encapsulates information about a single library that may be packed into the archive.
  *
@@ -33,11 +37,11 @@ public class Library {
 
 	private final String name;
 
-	private final File file;
+	private final @Nullable File file;
 
-	private final LibraryScope scope;
+	private final @Nullable LibraryScope scope;
 
-	private final LibraryCoordinates coordinates;
+	private final @Nullable LibraryCoordinates coordinates;
 
 	private final boolean unpackRequired;
 
@@ -67,9 +71,9 @@ public class Library {
 	 * @param included if the library is included in the uber jar
 	 * @since 2.4.8
 	 */
-	public Library(String name, File file, LibraryScope scope, LibraryCoordinates coordinates, boolean unpackRequired,
-			boolean local, boolean included) {
-		this.name = (name != null) ? name : file.getName();
+	public Library(@Nullable String name, @Nullable File file, @Nullable LibraryScope scope,
+			@Nullable LibraryCoordinates coordinates, boolean unpackRequired, boolean local, boolean included) {
+		this.name = (name != null) ? name : getFileName(file);
 		this.file = file;
 		this.scope = scope;
 		this.coordinates = coordinates;
@@ -78,6 +82,11 @@ public class Library {
 		this.included = included;
 	}
 
+	private static String getFileName(@Nullable File file) {
+		Assert.state(file != null, "'file' must not be null");
+		return file.getName();
+	}
+
 	/**
 	 * Return the name of file as it should be written.
 	 * @return the name
@@ -90,7 +99,7 @@ public class Library {
 	 * Return the library file.
 	 * @return the file
 	 */
-	public File getFile() {
+	public @Nullable File getFile() {
 		return this.file;
 	}
 
@@ -107,7 +116,7 @@ public class Library {
 	 * Return the scope of the library.
 	 * @return the scope
 	 */
-	public LibraryScope getScope() {
+	public @Nullable LibraryScope getScope() {
 		return this.scope;
 	}
 
@@ -115,7 +124,7 @@ public class Library {
 	 * Return the {@linkplain LibraryCoordinates coordinates} of the library.
 	 * @return the coordinates
 	 */
-	public LibraryCoordinates getCoordinates() {
+	public @Nullable LibraryCoordinates getCoordinates() {
 		return this.coordinates;
 	}
 
@@ -129,6 +138,7 @@ public class Library {
 	}
 
 	long getLastModified() {
+		Assert.state(this.file != null, "'file' must not be null");
 		return this.file.lastModified();
 	}
 

loader/spring-boot-loader-tools/src/main/java/org/springframework/boot/loader/tools/LibraryCoordinates.java

@@ -16,6 +16,8 @@
 
 package org.springframework.boot.loader.tools;
 
+import org.jspecify.annotations.Nullable;
+
 /**
  * Encapsulates information about the artifact coordinates of a library.
  *
@@ -60,7 +62,7 @@ public interface LibraryCoordinates {
 	 * @param coordinates the coordinates to convert (may be {@code null})
 	 * @return the standard notation form or {@code "::"} when the coordinates are null
 	 */
-	static String toStandardNotationString(LibraryCoordinates coordinates) {
+	static String toStandardNotationString(@Nullable LibraryCoordinates coordinates) {
 		if (coordinates == null) {
 			return "::";
 		}

loader/spring-boot-loader-tools/src/main/java/org/springframework/boot/loader/tools/MainClassFinder.java

@@ -36,6 +36,8 @@ import java.util.Set;
 import java.util.jar.JarEntry;
 import java.util.jar.JarFile;
 
+import org.jspecify.annotations.Nullable;
+
 import org.springframework.asm.AnnotationVisitor;
 import org.springframework.asm.ClassReader;
 import org.springframework.asm.ClassVisitor;
@@ -80,7 +82,7 @@ public abstract class MainClassFinder {
 	 * @return the main class or {@code null}
 	 * @throws IOException if the directory cannot be read
 	 */
-	public static String findMainClass(File rootDirectory) throws IOException {
+	public static @Nullable String findMainClass(File rootDirectory) throws IOException {
 		return doWithMainClasses(rootDirectory, MainClass::getName);
 	}
 
@@ -90,7 +92,7 @@ public abstract class MainClassFinder {
 	 * @return the main class or {@code null}
 	 * @throws IOException if the directory cannot be read
 	 */
-	public static String findSingleMainClass(File rootDirectory) throws IOException {
+	public static @Nullable String findSingleMainClass(File rootDirectory) throws IOException {
 		return findSingleMainClass(rootDirectory, null);
 	}
 
@@ -104,7 +106,8 @@ public abstract class MainClassFinder {
 	 * @return the main class or {@code null}
 	 * @throws IOException if the directory cannot be read
 	 */
-	public static String findSingleMainClass(File rootDirectory, String annotationName) throws IOException {
+	public static @Nullable String findSingleMainClass(File rootDirectory, @Nullable String annotationName)
+			throws IOException {
 		SingleMainClassCallback callback = new SingleMainClassCallback(annotationName);
 		MainClassFinder.doWithMainClasses(rootDirectory, callback);
 		return callback.getMainClassName();
@@ -119,7 +122,7 @@ public abstract class MainClassFinder {
 	 * @return the first callback result or {@code null}
 	 * @throws IOException in case of I/O errors
 	 */
-	static <T> T doWithMainClasses(File rootDirectory, MainClassCallback<T> callback) throws IOException {
+	static <T> @Nullable T doWithMainClasses(File rootDirectory, MainClassCallback<T> callback) throws IOException {
 		if (!rootDirectory.exists()) {
 			return null; // nothing to do
 		}
@@ -165,7 +168,7 @@ public abstract class MainClassFinder {
 	 * @return the main class or {@code null}
 	 * @throws IOException if the jar file cannot be read
 	 */
-	public static String findMainClass(JarFile jarFile, String classesLocation) throws IOException {
+	public static @Nullable String findMainClass(JarFile jarFile, String classesLocation) throws IOException {
 		return doWithMainClasses(jarFile, classesLocation, MainClass::getName);
 	}
 
@@ -176,7 +179,7 @@ public abstract class MainClassFinder {
 	 * @return the main class or {@code null}
 	 * @throws IOException if the jar file cannot be read
 	 */
-	public static String findSingleMainClass(JarFile jarFile, String classesLocation) throws IOException {
+	public static @Nullable String findSingleMainClass(JarFile jarFile, String classesLocation) throws IOException {
 		return findSingleMainClass(jarFile, classesLocation, null);
 	}
 
@@ -191,8 +194,8 @@ public abstract class MainClassFinder {
 	 * @return the main class or {@code null}
 	 * @throws IOException if the jar file cannot be read
 	 */
-	public static String findSingleMainClass(JarFile jarFile, String classesLocation, String annotationName)
-			throws IOException {
+	public static @Nullable String findSingleMainClass(JarFile jarFile, String classesLocation,
+			@Nullable String annotationName) throws IOException {
 		SingleMainClassCallback callback = new SingleMainClassCallback(annotationName);
 		MainClassFinder.doWithMainClasses(jarFile, classesLocation, callback);
 		return callback.getMainClassName();
@@ -207,7 +210,7 @@ public abstract class MainClassFinder {
 	 * @return the first callback result or {@code null}
 	 * @throws IOException in case of I/O errors
 	 */
-	static <T> T doWithMainClasses(JarFile jarFile, String classesLocation, MainClassCallback<T> callback)
+	static <T> @Nullable T doWithMainClasses(JarFile jarFile, String classesLocation, MainClassCallback<T> callback)
 			throws IOException {
 		List<JarEntry> classEntries = getClassEntries(jarFile, classesLocation);
 		classEntries.sort(new ClassEntryComparator());
@@ -226,7 +229,7 @@ public abstract class MainClassFinder {
 		return null;
 	}
 
-	private static String convertToClassName(String name, String prefix) {
+	private static String convertToClassName(String name, @Nullable String prefix) {
 		name = name.replace('/', '.');
 		name = name.replace('\\', '.');
 		name = name.substring(0, name.length() - DOT_CLASS.length());
@@ -236,7 +239,7 @@ public abstract class MainClassFinder {
 		return name;
 	}
 
-	private static List<JarEntry> getClassEntries(JarFile source, String classesLocation) {
+	private static List<JarEntry> getClassEntries(JarFile source, @Nullable String classesLocation) {
 		classesLocation = (classesLocation != null) ? classesLocation : "";
 		Enumeration<JarEntry> sourceEntries = source.entries();
 		List<JarEntry> classEntries = new ArrayList<>();
@@ -249,7 +252,7 @@ public abstract class MainClassFinder {
 		return classEntries;
 	}
 
-	private static ClassDescriptor createClassDescriptor(InputStream inputStream) {
+	private static @Nullable ClassDescriptor createClassDescriptor(InputStream inputStream) {
 		try {
 			ClassReader classReader = new ClassReader(inputStream);
 			ClassDescriptor classDescriptor = new ClassDescriptor();
@@ -291,13 +294,14 @@ public abstract class MainClassFinder {
 		}
 
 		@Override
-		public AnnotationVisitor visitAnnotation(String desc, boolean visible) {
+		public @Nullable AnnotationVisitor visitAnnotation(String desc, boolean visible) {
 			this.annotationNames.add(Type.getType(desc).getClassName());
 			return null;
 		}
 
 		@Override
-		public MethodVisitor visitMethod(int access, String name, String desc, String signature, String[] exceptions) {
+		public @Nullable MethodVisitor visitMethod(int access, String name, String desc, String signature,
+				String[] exceptions) {
 			if (isAccess(access, Opcodes.ACC_PUBLIC, Opcodes.ACC_STATIC) && MAIN_METHOD_NAME.equals(name)
 					&& MAIN_METHOD_TYPE.getDescriptor().equals(desc)) {
 				this.mainMethodFound = true;
@@ -336,7 +340,7 @@ public abstract class MainClassFinder {
 		 * @param mainClass the main class
 		 * @return a non-null value if processing should end or {@code null} to continue
 		 */
-		T doWith(MainClass mainClass);
+		@Nullable T doWith(MainClass mainClass);
 
 	}
 
@@ -370,7 +374,7 @@ public abstract class MainClassFinder {
 		}
 
 		@Override
-		public boolean equals(Object obj) {
+		public boolean equals(@Nullable Object obj) {
 			if (this == obj) {
 				return true;
 			}
@@ -404,19 +408,19 @@ public abstract class MainClassFinder {
 
 		private final Set<MainClass> mainClasses = new LinkedHashSet<>();
 
-		private final String annotationName;
+		private final @Nullable String annotationName;
 
-		private SingleMainClassCallback(String annotationName) {
+		private SingleMainClassCallback(@Nullable String annotationName) {
 			this.annotationName = annotationName;
 		}
 
 		@Override
-		public Object doWith(MainClass mainClass) {
+		public @Nullable Object doWith(MainClass mainClass) {
 			this.mainClasses.add(mainClass);
 			return null;
 		}
 
-		private String getMainClassName() {
+		private @Nullable String getMainClassName() {
 			Set<MainClass> matchingMainClasses = new LinkedHashSet<>();
 			if (this.annotationName != null) {
 				for (MainClass mainClass : this.mainClasses) {

loader/spring-boot-loader-tools/src/main/java/org/springframework/boot/loader/tools/Packager.java

@@ -39,6 +39,7 @@ import java.util.jar.Manifest;
 import java.util.zip.ZipEntry;
 
 import org.apache.commons.compress.archivers.jar.JarArchiveEntry;
+import org.jspecify.annotations.Nullable;
 
 import org.springframework.boot.loader.tools.AbstractJarWriter.EntryTransformer;
 import org.springframework.boot.loader.tools.AbstractJarWriter.UnpackHandler;
@@ -84,21 +85,21 @@ public abstract class Packager {
 
 	private final List<MainClassTimeoutWarningListener> mainClassTimeoutListeners = new ArrayList<>();
 
-	private String mainClass;
+	private @Nullable String mainClass;
 
 	private final File source;
 
-	private File backupFile;
+	private @Nullable File backupFile;
 
-	private Layout layout;
+	private @Nullable Layout layout;
 
-	private LoaderImplementation loaderImplementation;
+	private @Nullable LoaderImplementation loaderImplementation;
 
-	private LayoutFactory layoutFactory;
+	private @Nullable LayoutFactory layoutFactory;
 
-	private Layers layers;
+	private @Nullable Layers layers;
 
-	private LayersIndex layersIndex;
+	private @Nullable LayersIndex layersIndex;
 
 	private boolean includeRelevantJarModeJars = true;
 
@@ -128,7 +129,7 @@ public abstract class Packager {
 	 * searched for a suitable class.
 	 * @param mainClass the main class name
 	 */
-	public void setMainClass(String mainClass) {
+	public void setMainClass(@Nullable String mainClass) {
 		this.mainClass = mainClass;
 	}
 
@@ -145,7 +146,7 @@ public abstract class Packager {
 	 * Sets the loader implementation to use.
 	 * @param loaderImplementation the loaderImplementation to set
 	 */
-	public void setLoaderImplementation(LoaderImplementation loaderImplementation) {
+	public void setLoaderImplementation(@Nullable LoaderImplementation loaderImplementation) {
 		this.loaderImplementation = loaderImplementation;
 	}
 
@@ -154,7 +155,7 @@ public abstract class Packager {
 	 * layout is specified.
 	 * @param layoutFactory the layout factory to set
 	 */
-	public void setLayoutFactory(LayoutFactory layoutFactory) {
+	public void setLayoutFactory(@Nullable LayoutFactory layoutFactory) {
 		this.layoutFactory = layoutFactory;
 	}
 
@@ -172,7 +173,7 @@ public abstract class Packager {
 	 * Sets the {@link File} to use to back up the original source.
 	 * @param backupFile the file to use to back up the original source
 	 */
-	protected void setBackupFile(File backupFile) {
+	protected void setBackupFile(@Nullable File backupFile) {
 		this.backupFile = backupFile;
 	}
 
@@ -260,8 +261,11 @@ public abstract class Packager {
 	}
 
 	private void writeLayerIndex(AbstractJarWriter writer) throws IOException {
+		Assert.state(this.layout != null, "'layout' must not be null");
 		String name = this.layout.getLayersIndexFileLocation();
 		if (StringUtils.hasLength(name)) {
+			Assert.state(this.layers != null, "'layers' must not be null");
+			Assert.state(this.layersIndex != null, "'layersIndex' must not be null");
 			Layer layer = this.layers.getLayer(name);
 			this.layersIndex.add(layer, name);
 			writer.writeEntry(name, this.layersIndex::writeTo);
@@ -335,7 +339,7 @@ public abstract class Packager {
 		}
 	}
 
-	private String getMainClass(JarFile source, Manifest manifest) throws IOException {
+	private @Nullable String getMainClass(JarFile source, Manifest manifest) throws IOException {
 		if (this.mainClass != null) {
 			return this.mainClass;
 		}
@@ -346,7 +350,7 @@ public abstract class Packager {
 		return findMainMethodWithTimeoutWarning(source);
 	}
 
-	private String findMainMethodWithTimeoutWarning(JarFile source) throws IOException {
+	private @Nullable String findMainMethodWithTimeoutWarning(JarFile source) throws IOException {
 		long startTime = System.currentTimeMillis();
 		String mainMethod = findMainMethod(source);
 		long duration = System.currentTimeMillis() - startTime;
@@ -358,7 +362,7 @@ public abstract class Packager {
 		return mainMethod;
 	}
 
-	protected String findMainMethod(JarFile source) throws IOException {
+	protected @Nullable String findMainMethod(JarFile source) throws IOException {
 		return MainClassFinder.findSingleMainClass(source, getLayout().getClassesLocation(),
 				SPRING_BOOT_APPLICATION_CLASS_NAME);
 	}
@@ -434,7 +438,7 @@ public abstract class Packager {
 		return entry.getName().endsWith(".cdx.json") || entry.getName().endsWith("/bom.json");
 	}
 
-	private void putIfHasLength(Attributes attributes, String name, String value) {
+	private void putIfHasLength(Attributes attributes, String name, @Nullable String value) {
 		if (StringUtils.hasLength(value)) {
 			attributes.putValue(name, value);
 		}
@@ -456,7 +460,7 @@ public abstract class Packager {
 		 * @param duration the amount of time it took to find the main method
 		 * @param mainMethod the main method that was actually found
 		 */
-		void handleTimeoutWarning(long duration, String mainMethod);
+		void handleTimeoutWarning(long duration, @Nullable String mainMethod);
 
 	}
 
@@ -472,7 +476,7 @@ public abstract class Packager {
 		}
 
 		@Override
-		public JarArchiveEntry transform(JarArchiveEntry entry) {
+		public @Nullable JarArchiveEntry transform(JarArchiveEntry entry) {
 			if (entry.getName().equals("META-INF/INDEX.LIST")) {
 				return null;
 			}
@@ -528,7 +532,7 @@ public abstract class Packager {
 
 		private final UnpackHandler unpackHandler;
 
-		private final Function<JarEntry, Library> libraryLookup;
+		private final Function<JarEntry, @Nullable Library> libraryLookup;
 
 		PackagedLibraries(Libraries libraries, boolean ensureReproducibleBuild) throws IOException {
 			this.libraries = (ensureReproducibleBuild) ? new TreeMap<>() : new LinkedHashMap<>();
@@ -553,7 +557,7 @@ public abstract class Packager {
 			}
 		}
 
-		private Library lookup(JarEntry entry) {
+		private @Nullable Library lookup(JarEntry entry) {
 			return this.libraries.get(entry.getName());
 		}
 
@@ -561,7 +565,7 @@ public abstract class Packager {
 			return this.unpackHandler;
 		}
 
-		Function<JarEntry, Library> getLibraryLookup() {
+		Function<JarEntry, @Nullable Library> getLibraryLookup() {
 			return this.libraryLookup;
 		}
 

loader/spring-boot-loader-tools/src/main/java/org/springframework/boot/loader/tools/Repackager.java

@@ -23,6 +23,8 @@ import java.util.Locale;
 import java.util.Map;
 import java.util.jar.JarFile;
 
+import org.jspecify.annotations.Nullable;
+
 import org.springframework.util.Assert;
 
 /**
@@ -103,7 +105,8 @@ public class Repackager extends Packager {
 	 * @throws IOException if the file cannot be repackaged
 	 * @since 1.3.0
 	 */
-	public void repackage(File destination, Libraries libraries, LaunchScript launchScript) throws IOException {
+	public void repackage(File destination, Libraries libraries, @Nullable LaunchScript launchScript)
+			throws IOException {
 		repackage(destination, libraries, launchScript, null);
 	}
 
@@ -118,8 +121,8 @@ public class Repackager extends Packager {
 	 * @throws IOException if the file cannot be repackaged
 	 * @since 2.3.0
 	 */
-	public void repackage(File destination, Libraries libraries, LaunchScript launchScript, FileTime lastModifiedTime)
-			throws IOException {
+	public void repackage(File destination, Libraries libraries, @Nullable LaunchScript launchScript,
+			@Nullable FileTime lastModifiedTime) throws IOException {
 		Assert.isTrue(destination != null && !destination.isDirectory(), "Invalid destination");
 		getLayout(); // get layout early
 		destination = destination.getAbsoluteFile();
@@ -146,8 +149,8 @@ public class Repackager extends Packager {
 		}
 	}
 
-	private void repackage(JarFile sourceJar, File destination, Libraries libraries, LaunchScript launchScript,
-			FileTime lastModifiedTime) throws IOException {
+	private void repackage(JarFile sourceJar, File destination, Libraries libraries,
+			@Nullable LaunchScript launchScript, @Nullable FileTime lastModifiedTime) throws IOException {
 		try (JarWriter writer = new JarWriter(destination, launchScript, lastModifiedTime)) {
 			write(sourceJar, libraries, writer, lastModifiedTime != null);
 		}

loader/spring-boot-loader-tools/src/main/java/org/springframework/boot/loader/tools/RunProcess.java

@@ -23,6 +23,8 @@ import java.util.Collection;
 import java.util.Collections;
 import java.util.Map;
 
+import org.jspecify.annotations.Nullable;
+
 /**
  * Utility used to run a process.
  *
@@ -37,11 +39,11 @@ public class RunProcess {
 
 	private static final long JUST_ENDED_LIMIT = 500;
 
-	private final File workingDirectory;
+	private final @Nullable File workingDirectory;
 
 	private final String[] command;
 
-	private volatile Process process;
+	private volatile @Nullable Process process;
 
 	private volatile long endTime;
 
@@ -60,7 +62,7 @@ public class RunProcess {
 	 * to run in the working directory of the current Java process
 	 * @param command the program to execute and its arguments
 	 */
-	public RunProcess(File workingDirectory, String... command) {
+	public RunProcess(@Nullable File workingDirectory, String... command) {
 		this.workingDirectory = workingDirectory;
 		this.command = command;
 	}
@@ -104,7 +106,7 @@ public class RunProcess {
 	 * Return the running process.
 	 * @return the process or {@code null}
 	 */
-	public Process getRunningProcess() {
+	public @Nullable Process getRunningProcess() {
 		return this.process;
 	}
 

loader/spring-boot-loader-tools/src/main/java/org/springframework/boot/loader/tools/SizeCalculatingEntryWriter.java

@@ -26,6 +26,9 @@ import java.io.IOException;
 import java.io.InputStream;
 import java.io.OutputStream;
 
+import org.jspecify.annotations.Nullable;
+
+import org.springframework.util.Assert;
 import org.springframework.util.StreamUtils;
 
 /**
@@ -74,7 +77,7 @@ final class SizeCalculatingEntryWriter implements EntryWriter {
 		return this.size;
 	}
 
-	static EntryWriter get(EntryWriter entryWriter) throws IOException {
+	static @Nullable EntryWriter get(@Nullable EntryWriter entryWriter) throws IOException {
 		if (entryWriter == null || entryWriter.size() != -1) {
 			return entryWriter;
 		}
@@ -88,7 +91,7 @@ final class SizeCalculatingEntryWriter implements EntryWriter {
 
 		private int size = 0;
 
-		private File tempFile;
+		private @Nullable File tempFile;
 
 		private OutputStream outputStream;
 
@@ -131,8 +134,10 @@ final class SizeCalculatingEntryWriter implements EntryWriter {
 		}
 
 		Object getContent() {
-			return (this.outputStream instanceof ByteArrayOutputStream byteArrayOutputStream)
+			Object result = (this.outputStream instanceof ByteArrayOutputStream byteArrayOutputStream)
 					? byteArrayOutputStream.toByteArray() : this.tempFile;
+			Assert.state(result != null, "'result' must not be null");
+			return result;
 		}
 
 		int getSize() {

loader/spring-boot-loader-tools/src/main/java/org/springframework/boot/loader/tools/ZipHeaderPeekInputStream.java

@@ -22,6 +22,8 @@ import java.io.IOException;
 import java.io.InputStream;
 import java.util.Arrays;
 
+import org.jspecify.annotations.Nullable;
+
 /**
  * {@link InputStream} that can peek ahead at zip header bytes.
  *
@@ -37,7 +39,7 @@ class ZipHeaderPeekInputStream extends FilterInputStream {
 
 	private int position;
 
-	private ByteArrayInputStream headerStream;
+	private @Nullable ByteArrayInputStream headerStream;
 
 	protected ZipHeaderPeekInputStream(InputStream in) throws IOException {
 		super(in);

loader/spring-boot-loader-tools/src/main/java/org/springframework/boot/loader/tools/layer/IncludeExcludeContentSelector.java

@@ -20,6 +20,8 @@ import java.util.Collections;
 import java.util.List;
 import java.util.function.Function;
 
+import org.jspecify.annotations.Nullable;
+
 import org.springframework.boot.loader.tools.Layer;
 import org.springframework.util.Assert;
 
@@ -45,7 +47,7 @@ public class IncludeExcludeContentSelector<T> implements ContentSelector<T> {
 		this(layer, includes, excludes, Function.identity());
 	}
 
-	public <S> IncludeExcludeContentSelector(Layer layer, List<S> includes, List<S> excludes,
+	public <S> IncludeExcludeContentSelector(Layer layer, @Nullable List<S> includes, @Nullable List<S> excludes,
 			Function<S, ContentFilter<T>> filterFactory) {
 		Assert.notNull(layer, "'layer' must not be null");
 		Assert.notNull(filterFactory, "'filterFactory' must not be null");

loader/spring-boot-loader-tools/src/main/java/org/springframework/boot/loader/tools/layer/package-info.java

@@ -16,6 +16,8 @@
 
 /**
  * Classes used to support layer customization.
- *
  */
+@NullMarked
 package org.springframework.boot.loader.tools.layer;
+
+import org.jspecify.annotations.NullMarked;

loader/spring-boot-loader-tools/src/main/java/org/springframework/boot/loader/tools/package-info.java

@@ -17,4 +17,7 @@
 /**
  * Tools for generating executable JAR/WAR files.
  */
+@NullMarked
 package org.springframework.boot.loader.tools;
+
+import org.jspecify.annotations.NullMarked;