General defensiveness about the bootstrap ClassLoader (i.e. null ClassLoader)

Issue: SPR-11721
(cherry picked from commit c05ab3e)

Author: jhoeller

spring-core/src/main/java/org/springframework/core/io/ClassPathResource.java

@@ -1,5 +1,5 @@
 /*
- * Copyright 2002-2012 the original author or authors.
+ * Copyright 2002-2014 the original author or authors.
  *
  * Licensed under the Apache License, Version 2.0 (the "License");
  * you may not use this file except in compliance with the License.
@@ -50,9 +50,9 @@ public class ClassPathResource extends AbstractFileResolvingResource {
 
 
 	/**
-	 * Create a new ClassPathResource for ClassLoader usage.
-	 * A leading slash will be removed, as the ClassLoader
-	 * resource access methods will not accept it.
+	 * Create a new {@code ClassPathResource} for {@code ClassLoader} usage.
+	 * A leading slash will be removed, as the ClassLoader resource access
+	 * methods will not accept it.
 	 * <p>The thread context class loader will be used for
 	 * loading the resource.
 	 * @param path the absolute path within the class path
@@ -64,9 +64,9 @@ public ClassPathResource(String path) {
 	}
 
 	/**
-	 * Create a new ClassPathResource for ClassLoader usage.
-	 * A leading slash will be removed, as the ClassLoader
-	 * resource access methods will not accept it.
+	 * Create a new {@code ClassPathResource} for {@code ClassLoader} usage.
+	 * A leading slash will be removed, as the ClassLoader resource access
+	 * methods will not accept it.
 	 * @param path the absolute path within the classpath
 	 * @param classLoader the class loader to load the resource with,
 	 * or {@code null} for the thread context class loader
@@ -83,9 +83,9 @@ public ClassPathResource(String path, ClassLoader classLoader) {
 	}
 
 	/**
-	 * Create a new ClassPathResource for Class usage.
-	 * The path can be relative to the given class,
-	 * or absolute within the classpath via a leading slash.
+	 * Create a new {@code ClassPathResource} for {@code Class} usage.
+	 * The path can be relative to the given class, or absolute within
+	 * the classpath via a leading slash.
 	 * @param path relative or absolute path within the class path
 	 * @param clazz the class to load resources with
 	 * @see java.lang.Class#getResourceAsStream
@@ -97,8 +97,8 @@ public ClassPathResource(String path, Class<?> clazz) {
 	}
 
 	/**
-	 * Create a new ClassPathResource with optional ClassLoader and Class.
-	 * Only for internal usage.
+	 * Create a new {@code ClassPathResource} with optional {@code ClassLoader}
+	 * and {@code Class}. Only for internal usage.
 	 * @param path relative or absolute path within the classpath
 	 * @param classLoader the class loader to load the resource with, if any
 	 * @param clazz the class to load resources with, if any
@@ -109,6 +109,7 @@ protected ClassPathResource(String path, ClassLoader classLoader, Class<?> clazz
 		this.clazz = clazz;
 	}
 
+
 	/**
 	 * Return the path for this resource (as resource path within the class path).
 	 */
@@ -120,24 +121,34 @@ public final String getPath() {
 	 * Return the ClassLoader that this resource will be obtained from.
 	 */
 	public final ClassLoader getClassLoader() {
-		return (this.classLoader != null ? this.classLoader : this.clazz.getClassLoader());
+		return (this.clazz != null ? this.clazz.getClassLoader() : this.classLoader);
 	}
 
+
 	/**
 	 * This implementation checks for the resolution of a resource URL.
 	 * @see java.lang.ClassLoader#getResource(String)
 	 * @see java.lang.Class#getResource(String)
 	 */
 	@Override
 	public boolean exists() {
-		URL url;
+		return (resolveURL() != null);
+	}
+
+	/**
+	 * Resolves a URL for the underlying class path resource.
+	 * @return the resolved URL, or {@code null} if not resolvable
+	 */
+	protected URL resolveURL() {
 		if (this.clazz != null) {
-			url = this.clazz.getResource(this.path);
+			return this.clazz.getResource(this.path);
+		}
+		else if (this.classLoader != null) {
+			return this.classLoader.getResource(this.path);
 		}
 		else {
-			url = this.classLoader.getResource(this.path);
+			return ClassLoader.getSystemResource(this.path);
 		}
-		return (url != null);
 	}
 
 	/**
@@ -151,29 +162,27 @@ public InputStream getInputStream() throws IOException {
 		if (this.clazz != null) {
 			is = this.clazz.getResourceAsStream(this.path);
 		}
-		else {
+		else if (this.classLoader != null) {
 			is = this.classLoader.getResourceAsStream(this.path);
 		}
+		else {
+			is = ClassLoader.getSystemResourceAsStream(this.path);
+		}
 		if (is == null) {
 			throw new FileNotFoundException(getDescription() + " cannot be opened because it does not exist");
 		}
 		return is;
 	}
 
 	/**
-	 * This implementation returns a URL for the underlying class path resource.
+	 * This implementation returns a URL for the underlying class path resource,
+	 * if available.
 	 * @see java.lang.ClassLoader#getResource(String)
 	 * @see java.lang.Class#getResource(String)
 	 */
 	@Override
 	public URL getURL() throws IOException {
-		URL url;
-		if (this.clazz != null) {
-			url = this.clazz.getResource(this.path);
-		}
-		else {
-			url = this.classLoader.getResource(this.path);
-		}
+		URL url = resolveURL();
 		if (url == null) {
 			throw new FileNotFoundException(getDescription() + " cannot be resolved to URL because it does not exist");
 		}

spring-core/src/main/java/org/springframework/core/io/ResourceLoader.java

@@ -1,5 +1,5 @@
 /*
- * Copyright 2002-2012 the original author or authors.
+ * Copyright 2002-2014 the original author or authors.
  *
  * Licensed under the Apache License, Version 2.0 (the "License");
  * you may not use this file except in compliance with the License.
@@ -70,7 +70,9 @@ public interface ResourceLoader {
 	 * <p>Clients which need to access the ClassLoader directly can do so
 	 * in a uniform manner with the ResourceLoader, rather than relying
 	 * on the thread context ClassLoader.
-	 * @return the ClassLoader (never {@code null})
+	 * @return the ClassLoader (only {@code null} if even the system
+	 * ClassLoader isn't accessible)
+	 * @see org.springframework.util.ClassUtils#getDefaultClassLoader()
 	 */
 	ClassLoader getClassLoader();
 

spring-core/src/main/java/org/springframework/core/io/support/PathMatchingResourcePatternResolver.java

@@ -1,5 +1,5 @@
 /*
- * Copyright 2002-2013 the original author or authors.
+ * Copyright 2002-2014 the original author or authors.
  *
  * Licensed under the Apache License, Version 2.0 (the "License");
  * you may not use this file except in compliance with the License.
@@ -229,7 +229,8 @@ public ResourceLoader getResourceLoader() {
 
 	/**
 	 * Return the ClassLoader that this pattern resolver works with
-	 * (never {@code null}).
+	 * (only {@code null} if even the system ClassLoader isn't accessible).
+	 * @see org.springframework.util.ClassUtils#getDefaultClassLoader()
 	 */
 	@Override
 	public ClassLoader getClassLoader() {
@@ -301,7 +302,8 @@ protected Resource[] findAllClassPathResources(String location) throws IOExcepti
 		if (path.startsWith("/")) {
 			path = path.substring(1);
 		}
-		Enumeration<URL> resourceUrls = getClassLoader().getResources(path);
+		ClassLoader cl = getClassLoader();
+		Enumeration<URL> resourceUrls = (cl != null ? cl.getResources(path) : ClassLoader.getSystemResources(path));
 		Set<Resource> result = new LinkedHashSet<Resource>(16);
 		while (resourceUrls.hasMoreElements()) {
 			URL url = resourceUrls.nextElement();

spring-core/src/main/java/org/springframework/core/io/support/PropertiesLoaderUtils.java

@@ -1,5 +1,5 @@
 /*
- * Copyright 2002-2013 the original author or authors.
+ * Copyright 2002-2014 the original author or authors.
  *
  * Licensed under the Apache License, Version 2.0 (the "License");
  * you may not use this file except in compliance with the License.
@@ -170,12 +170,13 @@ public static Properties loadAllProperties(String resourceName) throws IOExcepti
 	 */
 	public static Properties loadAllProperties(String resourceName, ClassLoader classLoader) throws IOException {
 		Assert.notNull(resourceName, "Resource name must not be null");
-		ClassLoader clToUse = classLoader;
-		if (clToUse == null) {
-			clToUse = ClassUtils.getDefaultClassLoader();
+		ClassLoader classLoaderToUse = classLoader;
+		if (classLoaderToUse == null) {
+			classLoaderToUse = ClassUtils.getDefaultClassLoader();
 		}
 		Properties props = new Properties();
-		Enumeration<URL> urls = clToUse.getResources(resourceName);
+		Enumeration<URL> urls = (classLoaderToUse != null ? classLoaderToUse.getResources(resourceName) :
+				ClassLoader.getSystemResources(resourceName));
 		while (urls.hasMoreElements()) {
 			URL url = urls.nextElement();
 			URLConnection con = url.openConnection();

spring-core/src/main/java/org/springframework/core/io/support/SpringFactoriesLoader.java

@@ -67,16 +67,17 @@ public abstract class SpringFactoriesLoader {
 	 */
 	public static <T> List<T> loadFactories(Class<T> factoryClass, ClassLoader classLoader) {
 		Assert.notNull(factoryClass, "'factoryClass' must not be null");
-		if (classLoader == null) {
-			classLoader = SpringFactoriesLoader.class.getClassLoader();
+		ClassLoader classLoaderToUse = classLoader;
+		if (classLoaderToUse == null) {
+			classLoaderToUse = SpringFactoriesLoader.class.getClassLoader();
 		}
-		List<String> factoryNames = loadFactoryNames(factoryClass, classLoader);
+		List<String> factoryNames = loadFactoryNames(factoryClass, classLoaderToUse);
 		if (logger.isTraceEnabled()) {
 			logger.trace("Loaded [" + factoryClass.getName() + "] names: " + factoryNames);
 		}
 		List<T> result = new ArrayList<T>(factoryNames.size());
 		for (String factoryName : factoryNames) {
-			result.add(instantiateFactory(factoryName, factoryClass, classLoader));
+			result.add(instantiateFactory(factoryName, factoryClass, classLoaderToUse));
 		}
 		OrderComparator.sort(result);
 		return result;
@@ -86,7 +87,8 @@ public static List<String> loadFactoryNames(Class<?> factoryClass, ClassLoader c
 		String factoryClassName = factoryClass.getName();
 		try {
 			List<String> result = new ArrayList<String>();
-			Enumeration<URL> urls = classLoader.getResources(FACTORIES_RESOURCE_LOCATION);
+			Enumeration<URL> urls = (classLoader != null ? classLoader.getResources(FACTORIES_RESOURCE_LOCATION) :
+					ClassLoader.getSystemResources(FACTORIES_RESOURCE_LOCATION));
 			while (urls.hasMoreElements()) {
 				URL url = urls.nextElement();
 				Properties properties = PropertiesLoaderUtils.loadProperties(new UrlResource(url));

spring-core/src/main/java/org/springframework/util/ClassUtils.java

@@ -142,24 +142,35 @@ private static void registerCommonClasses(Class<?>... commonClasses) {
 	 * ClassLoader, if available; the ClassLoader that loaded the ClassUtils
 	 * class will be used as fallback.
 	 * <p>Call this method if you intend to use the thread context ClassLoader
-	 * in a scenario where you absolutely need a non-null ClassLoader reference:
+	 * in a scenario where you clearly prefer a non-null ClassLoader reference:
 	 * for example, for class path resource loading (but not necessarily for
 	 * {@code Class.forName}, which accepts a {@code null} ClassLoader
 	 * reference as well).
-	 * @return the default ClassLoader (never {@code null})
+	 * @return the default ClassLoader (only {@code null} if even the system
+	 * ClassLoader isn't accessible)
 	 * @see Thread#getContextClassLoader()
+	 * @see ClassLoader#getSystemClassLoader()
 	 */
 	public static ClassLoader getDefaultClassLoader() {
 		ClassLoader cl = null;
 		try {
 			cl = Thread.currentThread().getContextClassLoader();
 		}
 		catch (Throwable ex) {
-			// Cannot access thread context ClassLoader - falling back to system class loader...
+			// Cannot access thread context ClassLoader - falling back...
 		}
 		if (cl == null) {
 			// No thread context class loader -> use class loader of this class.
 			cl = ClassUtils.class.getClassLoader();
+			if (cl == null) {
+				// getClassLoader() returning null indicates the bootstrap ClassLoader
+				try {
+					cl = ClassLoader.getSystemClassLoader();
+				}
+				catch (Throwable ex) {
+					// Cannot access system ClassLoader - oh well, maybe the caller can live with null...
+				}
+			}
 		}
 		return cl;
 	}
@@ -185,7 +196,7 @@ public static ClassLoader overrideThreadContextClassLoader(ClassLoader classLoad
 
 	/**
 	 * Replacement for {@code Class.forName()} that also returns Class instances
-	 * for primitives (e.g."int") and array class names (e.g. "String[]").
+	 * for primitives (e.g. "int") and array class names (e.g. "String[]").
 	 * Furthermore, it is also capable of resolving inner class names in Java source
 	 * style (e.g. "java.lang.Thread.State" instead of "java.lang.Thread$State").
 	 * @param name the name of the Class
@@ -228,19 +239,19 @@ public static Class<?> forName(String name, ClassLoader classLoader) throws Clas
 			return Array.newInstance(elementClass, 0).getClass();
 		}
 
-		ClassLoader classLoaderToUse = classLoader;
-		if (classLoaderToUse == null) {
-			classLoaderToUse = getDefaultClassLoader();
+		ClassLoader clToUse = classLoader;
+		if (clToUse == null) {
+			clToUse = getDefaultClassLoader();
 		}
 		try {
-			return classLoaderToUse.loadClass(name);
+			return (clToUse != null ? clToUse.loadClass(name) : Class.forName(name));
 		}
 		catch (ClassNotFoundException ex) {
 			int lastDotIndex = name.lastIndexOf('.');
 			if (lastDotIndex != -1) {
 				String innerClassName = name.substring(0, lastDotIndex) + '$' + name.substring(lastDotIndex + 1);
 				try {
-					return classLoaderToUse.loadClass(innerClassName);
+					return (clToUse != null ? clToUse.loadClass(innerClassName) : Class.forName(innerClassName));
 				}
 				catch (ClassNotFoundException ex2) {
 					// swallow - let original exception get through

spring-core/src/main/java/org/springframework/util/ResourceUtils.java

@@ -116,7 +116,8 @@ public static URL getURL(String resourceLocation) throws FileNotFoundException {
 		Assert.notNull(resourceLocation, "Resource location must not be null");
 		if (resourceLocation.startsWith(CLASSPATH_URL_PREFIX)) {
 			String path = resourceLocation.substring(CLASSPATH_URL_PREFIX.length());
-			URL url = ClassUtils.getDefaultClassLoader().getResource(path);
+			ClassLoader cl = ClassUtils.getDefaultClassLoader();
+			URL url = (cl != null ? cl.getResource(path) : ClassLoader.getSystemResource(path));
 			if (url == null) {
 				String description = "class path resource [" + path + "]";
 				throw new FileNotFoundException(
@@ -156,7 +157,8 @@ public static File getFile(String resourceLocation) throws FileNotFoundException
 		if (resourceLocation.startsWith(CLASSPATH_URL_PREFIX)) {
 			String path = resourceLocation.substring(CLASSPATH_URL_PREFIX.length());
 			String description = "class path resource [" + path + "]";
-			URL url = ClassUtils.getDefaultClassLoader().getResource(path);
+			ClassLoader cl = ClassUtils.getDefaultClassLoader();
+			URL url = (cl != null ? cl.getResource(path) : ClassLoader.getSystemResource(path));
 			if (url == null) {
 				throw new FileNotFoundException(
 						description + " cannot be resolved to absolute file path " +