Fix exploded jar classloader issues

Fix a bug in `ExplodedURLClassLoader` and merge the code into the
existing `LaunchedURLClassLoader` class. Also polish a few method
names relating to layer support.

See gh-19848
See gh-19767

Author: philwebb

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

@@ -164,8 +164,8 @@ protected void postProcessClassPathArchives(List<Archive> archives) throws Excep
 	}
 
 	@Override
-	protected boolean supportsNestedJars() {
-		return this.archive.supportsNestedJars();
+	protected boolean isExploded() {
+		return this.archive.isExploded();
 	}
 
 	/**

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

@@ -42,17 +42,33 @@ public class LaunchedURLClassLoader extends URLClassLoader {
 		ClassLoader.registerAsParallelCapable();
 	}
 
+	private final boolean exploded;
+
 	/**
 	 * Create a new {@link LaunchedURLClassLoader} instance.
 	 * @param urls the URLs from which to load classes and resources
 	 * @param parent the parent class loader for delegation
 	 */
 	public LaunchedURLClassLoader(URL[] urls, ClassLoader parent) {
+		this(false, urls, parent);
+	}
+
+	/**
+	 * Create a new {@link LaunchedURLClassLoader} instance.
+	 * @param exploded the the underlying archive is exploded
+	 * @param urls the URLs from which to load classes and resources
+	 * @param parent the parent class loader for delegation
+	 */
+	public LaunchedURLClassLoader(boolean exploded, URL[] urls, ClassLoader parent) {
 		super(urls, parent);
+		this.exploded = exploded;
 	}
 
 	@Override
 	public URL findResource(String name) {
+		if (this.exploded) {
+			return super.findResource(name);
+		}
 		Handler.setUseFastConnectionExceptions(true);
 		try {
 			return super.findResource(name);
@@ -64,6 +80,9 @@ public URL findResource(String name) {
 
 	@Override
 	public Enumeration<URL> findResources(String name) throws IOException {
+		if (this.exploded) {
+			return super.findResources(name);
+		}
 		Handler.setUseFastConnectionExceptions(true);
 		try {
 			return new UseFastConnectionExceptionsEnumeration(super.findResources(name));
@@ -86,6 +105,9 @@ protected Class<?> loadClass(String name, boolean resolve) throws ClassNotFoundE
 			catch (ClassNotFoundException ex) {
 			}
 		}
+		if (this.exploded) {
+			return super.loadClass(name, resolve);
+		}
 		Handler.setUseFastConnectionExceptions(true);
 		try {
 			try {
@@ -168,6 +190,9 @@ private void definePackage(String className, String packageName) {
 	 * Clear URL caches.
 	 */
 	public void clearCache() {
+		if (this.exploded) {
+			return;
+		}
 		for (URL url : getURLs()) {
 			try {
 				URLConnection connection = url.openConnection();

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

@@ -49,7 +49,7 @@ public abstract class Launcher {
 	 * @throws Exception if the application fails to launch
 	 */
 	protected void launch(String[] args) throws Exception {
-		if (supportsNestedJars()) {
+		if (!isExploded()) {
 			JarFile.registerUrlProtocolHandler();
 		}
 		ClassLoader classLoader = createClassLoader(getClassPathArchivesIterator());
@@ -94,10 +94,7 @@ protected ClassLoader createClassLoader(Iterator<Archive> archives) throws Excep
 	 * @throws Exception if the classloader cannot be created
 	 */
 	protected ClassLoader createClassLoader(URL[] urls) throws Exception {
-		if (supportsNestedJars()) {
-			return new LaunchedURLClassLoader(urls, getClass().getClassLoader());
-		}
-		return new ExplodedURLClassLoader(urls, getClass().getClassLoader());
+		return new LaunchedURLClassLoader(isExploded(), urls, getClass().getClassLoader());
 	}
 
 	/**
@@ -168,12 +165,12 @@ protected final Archive createArchive() throws Exception {
 	}
 
 	/**
-	 * Returns if the launcher needs to support fully nested JARs. If this method returns
-	 * {@code false} then only regular JARs are supported and the additional URL and
-	 * ClassLoader support infrastructure will not be installed.
-	 * @return if nested JARs are supported
+	 * Returns if the launcher is running in an exploded mode. If this method returns
+	 * {@code true} then only regular JARs are supported and the additional URL and
+	 * ClassLoader support infrastructure can be optimized.
+	 * @return if the jar is exploded.
 	 */
-	protected boolean supportsNestedJars() {
+	protected boolean isExploded() {
 		return true;
 	}
 

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

@@ -90,8 +90,12 @@ default List<Archive> getNestedArchives(EntryFilter filter) throws IOException {
 	@Override
 	Iterator<Entry> iterator();
 
-	default boolean supportsNestedJars() {
-		return true;
+	/**
+	 * Return if the archive is exploded (already unpacked).
+	 * @return if the archive is exploded
+	 */
+	default boolean isExploded() {
+		return false;
 	}
 
 	/**

spring-boot-project/spring-boot-tools/spring-boot-loader/src/main/java/org/springframework/boot/loader/archive/Archive.java

@@ -114,8 +114,8 @@ protected Archive getNestedArchive(Entry entry) throws IOException {
 	}
 
 	@Override
-	public boolean supportsNestedJars() {
-		return false;
+	public boolean isExploded() {
+		return true;
 	}
 
 	@Override