Update Restarter to support for ClassLoaderFiles

Update the `Restarter` so that class files and resources can change
independently of the underlying source folders. This change will
allow updates to be pushed to a remotely running application, without
requiring the application to run in an exploded form.

See gh-3086

spring-boot-developer-tools/src/main/java/org/springframework/boot/developertools/restart/Restarter.java

@@ -22,9 +22,11 @@ import java.lang.reflect.Field;
 import java.lang.reflect.Method;
 import java.net.URL;
 import java.util.Arrays;
+import java.util.Collection;
 import java.util.HashMap;
 import java.util.IdentityHashMap;
 import java.util.Iterator;
+import java.util.LinkedHashSet;
 import java.util.LinkedList;
 import java.util.List;
 import java.util.Map;
@@ -41,6 +43,7 @@ import org.apache.commons.logging.LogFactory;
 import org.springframework.beans.CachedIntrospectionResults;
 import org.springframework.beans.factory.ObjectFactory;
 import org.springframework.boot.SpringApplication;
+import org.springframework.boot.developertools.restart.classloader.ClassLoaderFiles;
 import org.springframework.boot.developertools.restart.classloader.RestartClassLoader;
 import org.springframework.boot.logging.DeferredLog;
 import org.springframework.cglib.core.ClassNameReader;
@@ -81,7 +84,7 @@ public class Restarter {
 
 	private final boolean forceReferenceCleanup;
 
-	private URL[] urls;
+	private URL[] initialUrls;
 
 	private final String mainClassName;
 
@@ -91,6 +94,10 @@ public class Restarter {
 
 	private final UncaughtExceptionHandler exceptionHandler;
 
+	private final Set<URL> urls = new LinkedHashSet<URL>();
+
+	private final ClassLoaderFiles classLoaderFiles = new ClassLoaderFiles();
+
 	private final Map<String, Object> attributes = new HashMap<String, Object>();
 
 	private final BlockingDeque<LeakSafeThread> leakSafeThreads = new LinkedBlockingDeque<LeakSafeThread>();
@@ -115,7 +122,7 @@ public class Restarter {
 		this.logger.debug("Creating new Restarter for thread " + thread);
 		SilentExitExceptionHandler.setup(thread);
 		this.forceReferenceCleanup = forceReferenceCleanup;
-		this.urls = initializer.getInitialUrls(thread);
+		this.initialUrls = initializer.getInitialUrls(thread);
 		this.mainClassName = getMainClassName(thread);
 		this.applicationClassLoader = thread.getContextClassLoader();
 		this.args = args;
@@ -134,7 +141,8 @@ public class Restarter {
 
 	protected void initialize(boolean restartOnInitialize) {
 		preInitializeLeakyClasses();
-		if (this.urls != null) {
+		if (this.initialUrls != null) {
+			this.urls.addAll(Arrays.asList(this.initialUrls));
 			if (restartOnInitialize) {
 				this.logger.debug("Immediately restarting application");
 				immediateRestart();
@@ -176,6 +184,24 @@ public class Restarter {
 		}
 	}
 
+	/**
+	 * Add additional URLs to be includes in the next restart.
+	 * @param urls the urls to add
+	 */
+	public void addUrls(Collection<URL> urls) {
+		Assert.notNull(urls, "Urls must not be null");
+		this.urls.addAll(ChangeableUrls.fromUrls(urls).toList());
+	}
+
+	/**
+	 * Add additional {@link ClassLoaderFiles} to be included in the next restart.
+	 * @param classLoaderFiles the files to add
+	 */
+	public void addClassLoaderFiles(ClassLoaderFiles classLoaderFiles) {
+		Assert.notNull(classLoaderFiles, "ClassLoaderFiles must not be null");
+		this.classLoaderFiles.addAll(classLoaderFiles);
+	}
+
 	/**
 	 * Return a {@link ThreadFactory} that can be used to create leak safe threads.
 	 * @return a leak safe thread factory
@@ -208,10 +234,13 @@ public class Restarter {
 	protected void start() throws Exception {
 		Assert.notNull(this.mainClassName, "Unable to find the main class to restart");
 		ClassLoader parent = this.applicationClassLoader;
-		ClassLoader classLoader = new RestartClassLoader(parent, this.urls, this.logger);
+		URL[] urls = this.urls.toArray(new URL[this.urls.size()]);
+		ClassLoaderFiles updatedFiles = new ClassLoaderFiles(this.classLoaderFiles);
+		ClassLoader classLoader = new RestartClassLoader(parent, urls, updatedFiles,
+				this.logger);
 		if (this.logger.isDebugEnabled()) {
 			this.logger.debug("Starting application " + this.mainClassName
-					+ " with URLs " + Arrays.asList(this.urls));
+					+ " with URLs " + Arrays.asList(urls));
 		}
 		relaunch(classLoader);
 	}
@@ -369,7 +398,7 @@ public class Restarter {
 	 * @return the initial URLs or {@code null}
 	 */
 	public URL[] getInitialUrls() {
-		return this.urls;
+		return this.initialUrls;
 	}
 
 	/**

spring-boot-developer-tools/src/main/java/org/springframework/boot/developertools/restart/classloader/ClassLoaderFile.java

@@ -0,0 +1,112 @@
+/*
+ * Copyright 2012-2015 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.
+ * You may obtain a copy of the License at
+ *
+ *      http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+package org.springframework.boot.developertools.restart.classloader;
+
+import java.io.Serializable;
+
+import org.springframework.util.Assert;
+
+/**
+ * A single file that may be served from a {@link ClassLoader}. Can be used to represent
+ * files that have been added, modified or deleted since the original JAR was created.
+ *
+ * @author Phillip Webb
+ * @see ClassLoaderFileRepository
+ * @since 1.3.0
+ */
+public class ClassLoaderFile implements Serializable {
+
+	private static final long serialVersionUID = 1;
+
+	private final Kind kind;
+
+	private final byte[] contents;
+
+	private final long lastModified;
+
+	/**
+	 * Create a new {@link ClassLoaderFile} instance.
+	 * @param kind the kind of file
+	 * @param contents the file contents
+	 */
+	public ClassLoaderFile(Kind kind, byte[] contents) {
+		this(kind, System.currentTimeMillis(), contents);
+	}
+
+	/**
+	 * Create a new {@link ClassLoaderFile} instance.
+	 * @param kind the kind of file
+	 * @param lastModified the last modified time
+	 * @param contents the file contents
+	 */
+	public ClassLoaderFile(Kind kind, long lastModified, byte[] contents) {
+		Assert.notNull(kind, "Kind must not be null");
+		Assert.isTrue(kind == Kind.DELETED ? contents == null : contents != null,
+				"Contents must " + (kind == Kind.DELETED ? "" : "not ") + "be null");
+		this.kind = kind;
+		this.lastModified = lastModified;
+		this.contents = contents;
+	}
+
+	/**
+	 * Return the file {@link Kind} (added, modified, deleted).
+	 * @return the kind
+	 */
+	public Kind getKind() {
+		return this.kind;
+	}
+
+	/**
+	 * Return the time that the file was last modified.
+	 * @return the last modified time
+	 */
+	public long getLastModified() {
+		return this.lastModified;
+	}
+
+	/**
+	 * Return the contents of the file as a byte array or {@code null} if
+	 * {@link #getKind()} is {@link Kind#DELETED}.
+	 * @return the contents or {@code null}
+	 */
+	public byte[] getContents() {
+		return this.contents;
+	}
+
+	/**
+	 * The kinds of class load files.
+	 */
+	public static enum Kind {
+
+		/**
+		 * The file has been added since the original JAR was created.
+		 */
+		ADDED,
+
+		/**
+		 * The file has been modified since the original JAR was created.
+		 */
+		MODIFIED,
+
+		/**
+		 * The file has been deleted since the original JAR was created.
+		 */
+		DELETED
+
+	}
+
+}

spring-boot-developer-tools/src/main/java/org/springframework/boot/developertools/restart/classloader/ClassLoaderFileRepository.java

@@ -0,0 +1,50 @@
+/*
+ * Copyright 2012-2015 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.
+ * You may obtain a copy of the License at
+ *
+ *      http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+package org.springframework.boot.developertools.restart.classloader;
+
+/**
+ * A container for files that may be served from a {@link ClassLoader}. Can be used to
+ * represent files that have been added, modified or deleted since the original JAR was
+ * created.
+ *
+ * @author Phillip Webb
+ * @since 1.3.0
+ * @see ClassLoaderFile
+ */
+public interface ClassLoaderFileRepository {
+
+	/**
+	 * Empty {@link ClassLoaderFileRepository} implementation.
+	 */
+	public static final ClassLoaderFileRepository NONE = new ClassLoaderFileRepository() {
+
+		@Override
+		public ClassLoaderFile getFile(String name) {
+			return null;
+		}
+
+	};
+
+	/**
+	 * Return a {@link ClassLoaderFile} for the given name or {@code null} if no file is
+	 * contained in this collection.
+	 * @param name the name of the file
+	 * @return a {@link ClassLoaderFile} or {@code null}
+	 */
+	ClassLoaderFile getFile(String name);
+
+}

spring-boot-developer-tools/src/main/java/org/springframework/boot/developertools/restart/classloader/ClassLoaderFileURLStreamHandler.java

@@ -0,0 +1,67 @@
+/*
+ * Copyright 2012-2015 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.
+ * You may obtain a copy of the License at
+ *
+ *      http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+package org.springframework.boot.developertools.restart.classloader;
+
+import java.io.ByteArrayInputStream;
+import java.io.IOException;
+import java.io.InputStream;
+import java.net.URL;
+import java.net.URLConnection;
+import java.net.URLStreamHandler;
+
+/**
+ * {@link URLStreamHandler} for the contents of a {@link ClassLoaderFile}.
+ *
+ * @author Phillip Webb
+ */
+class ClassLoaderFileURLStreamHandler extends URLStreamHandler {
+
+	private ClassLoaderFile file;
+
+	public ClassLoaderFileURLStreamHandler(ClassLoaderFile file) {
+		this.file = file;
+	}
+
+	@Override
+	protected URLConnection openConnection(URL url) throws IOException {
+		return new Connection(url);
+	}
+
+	private class Connection extends URLConnection {
+
+		public Connection(URL url) {
+			super(url);
+		}
+
+		@Override
+		public void connect() throws IOException {
+		}
+
+		@Override
+		public InputStream getInputStream() throws IOException {
+			return new ByteArrayInputStream(
+					ClassLoaderFileURLStreamHandler.this.file.getContents());
+		}
+
+		@Override
+		public long getLastModified() {
+			return ClassLoaderFileURLStreamHandler.this.file.getLastModified();
+
+		}
+
+	}
+}

spring-boot-developer-tools/src/main/java/org/springframework/boot/developertools/restart/classloader/ClassLoaderFiles.java

@@ -0,0 +1,202 @@
+/*
+ * Copyright 2012-2015 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.
+ * You may obtain a copy of the License at
+ *
+ *      http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+package org.springframework.boot.developertools.restart.classloader;
+
+import java.io.Serializable;
+import java.util.Collection;
+import java.util.Collections;
+import java.util.LinkedHashMap;
+import java.util.Map;
+import java.util.Map.Entry;
+import java.util.Set;
+
+import javax.management.loading.ClassLoaderRepository;
+
+import org.springframework.util.Assert;
+
+/**
+ * {@link ClassLoaderFileRepository} that maintains a collection of
+ * {@link ClassLoaderFile} items grouped by source folders.
+ *
+ * @author Phillip Webb
+ * @since 1.3.0
+ * @see ClassLoaderFile
+ * @see ClassLoaderRepository
+ */
+public class ClassLoaderFiles implements ClassLoaderFileRepository, Serializable {
+
+	private static final long serialVersionUID = 1;
+
+	private final Map<String, SourceFolder> sourceFolders;
+
+	/**
+	 * Create a new {@link ClassLoaderFiles} instance.
+	 */
+	public ClassLoaderFiles() {
+		this.sourceFolders = new LinkedHashMap<String, SourceFolder>();
+	}
+
+	/**
+	 * Create a new {@link ClassLoaderFiles} instance.
+	 * @param classLoaderFiles the source classloader files.
+	 */
+	public ClassLoaderFiles(ClassLoaderFiles classLoaderFiles) {
+		Assert.notNull(classLoaderFiles, "ClassLoaderFiles must not be null");
+		this.sourceFolders = new LinkedHashMap<String, SourceFolder>(
+				classLoaderFiles.sourceFolders);
+	}
+
+	/**
+	 * Add all elements items from the specified {@link ClassLoaderFiles} to this
+	 * instance.
+	 * @param files the files to add
+	 */
+	public void addAll(ClassLoaderFiles files) {
+		Assert.notNull(files, "Files must not be null");
+		for (SourceFolder folder : files.getSourceFolders()) {
+			for (Map.Entry<String, ClassLoaderFile> entry : folder.getFilesEntrySet()) {
+				addFile(folder.getName(), entry.getKey(), entry.getValue());
+			}
+		}
+	}
+
+	/**
+	 * Add a single {@link ClassLoaderFile} to the collection.
+	 * @param name the name of the file
+	 * @param file the file to add
+	 */
+	public void addFile(String name, ClassLoaderFile file) {
+		addFile("", name, file);
+	}
+
+	/**
+	 * Add a single {@link ClassLoaderFile} to the collection.
+	 * @param sourceFolder the source folder of the file
+	 * @param name the name of the file
+	 * @param file the file to add
+	 */
+	public void addFile(String sourceFolder, String name, ClassLoaderFile file) {
+		Assert.notNull(sourceFolder, "SourceFolder must not be null");
+		Assert.notNull(name, "Name must not be null");
+		Assert.notNull(file, "File must not be null");
+		removeAll(name);
+		getOrCreateSourceFolder(sourceFolder).add(name, file);
+	}
+
+	private void removeAll(String name) {
+		for (SourceFolder sourceFolder : this.sourceFolders.values()) {
+			sourceFolder.remove(name);
+		}
+	}
+
+	/**
+	 * Get or create a {@link SourceFolder} with the given name.
+	 * @param name the name of the folder
+	 * @return an existing or newly added {@link SourceFolder}
+	 */
+	protected final SourceFolder getOrCreateSourceFolder(String name) {
+		SourceFolder sourceFolder = this.sourceFolders.get(name);
+		if (sourceFolder == null) {
+			sourceFolder = new SourceFolder(name);
+			this.sourceFolders.put(name, sourceFolder);
+		}
+		return sourceFolder;
+	}
+
+	/**
+	 * Return all {@link SourceFolder SourceFolders} that have been added to the
+	 * collection.
+	 * @return a collection of {@link SourceFolder} items
+	 */
+	public Collection<SourceFolder> getSourceFolders() {
+		return Collections.unmodifiableCollection(this.sourceFolders.values());
+	}
+
+	/**
+	 * Return the size of the collection.
+	 * @return the size of the collection
+	 */
+	public int size() {
+		int size = 0;
+		for (SourceFolder sourceFolder : this.sourceFolders.values()) {
+			size += sourceFolder.getFiles().size();
+		}
+		return size;
+	}
+
+	@Override
+	public ClassLoaderFile getFile(String name) {
+		for (SourceFolder sourceFolder : this.sourceFolders.values()) {
+			ClassLoaderFile file = sourceFolder.get(name);
+			if (file != null) {
+				return file;
+			}
+		}
+		return null;
+	}
+
+	/**
+	 * An individual source folder that is being managed by the collection.
+	 */
+	public static class SourceFolder implements Serializable {
+
+		private static final long serialVersionUID = 1;
+
+		private final String name;
+
+		private final Map<String, ClassLoaderFile> files = new LinkedHashMap<String, ClassLoaderFile>();
+
+		SourceFolder(String name) {
+			this.name = name;
+		}
+
+		public Set<Entry<String, ClassLoaderFile>> getFilesEntrySet() {
+			return this.files.entrySet();
+		}
+
+		protected final void add(String name, ClassLoaderFile file) {
+			this.files.put(name, file);
+		}
+
+		protected final void remove(String name) {
+			this.files.remove(name);
+		}
+
+		protected final ClassLoaderFile get(String name) {
+			return this.files.get(name);
+		}
+
+		/**
+		 * Return the name of the source folder.
+		 * @return the name of the source folder
+		 */
+		public String getName() {
+			return this.name;
+		}
+
+		/**
+		 * Return all {@link ClassLoaderFile ClassLoaderFiles} in the collection that are
+		 * contained in this source folder.
+		 * @return the files contained in the source folder
+		 */
+		public Collection<ClassLoaderFile> getFiles() {
+			return Collections.unmodifiableCollection(this.files.values());
+		}
+
+	}
+
+}

spring-boot-developer-tools/src/main/java/org/springframework/boot/developertools/restart/classloader/RestartClassLoader.java

@@ -17,12 +17,16 @@
 package org.springframework.boot.developertools.restart.classloader;
 
 import java.io.IOException;
+import java.net.MalformedURLException;
 import java.net.URL;
 import java.net.URLClassLoader;
+import java.security.AccessController;
+import java.security.PrivilegedAction;
 import java.util.Enumeration;
 
 import org.apache.commons.logging.Log;
 import org.apache.commons.logging.LogFactory;
+import org.springframework.boot.developertools.restart.classloader.ClassLoaderFile.Kind;
 import org.springframework.core.SmartClassLoader;
 import org.springframework.util.Assert;
 
@@ -38,25 +42,44 @@ public class RestartClassLoader extends URLClassLoader implements SmartClassLoad
 
 	private final Log logger;
 
+	private final ClassLoaderFileRepository updatedFiles;
+
 	/**
 	 * Create a new {@link RestartClassLoader} instance.
-	 * @param parent the parent classloader URLs were created.
+	 * @param parent the parent classloader
 	 * @param urls the urls managed by the classloader
 	 */
 	public RestartClassLoader(ClassLoader parent, URL[] urls) {
-		this(parent, urls, LogFactory.getLog(RestartClassLoader.class));
+		this(parent, urls, ClassLoaderFileRepository.NONE);
 	}
 
 	/**
 	 * Create a new {@link RestartClassLoader} instance.
-	 * @param parent the parent classloader URLs were created.
+	 * @param parent the parent classloader
+	 * @param updatedFiles any files that have been updated since the JARs referenced in
+	 * URLs were created.
+	 * @param urls the urls managed by the classloader
+	 */
+	public RestartClassLoader(ClassLoader parent, URL[] urls,
+			ClassLoaderFileRepository updatedFiles) {
+		this(parent, urls, updatedFiles, LogFactory.getLog(RestartClassLoader.class));
+	}
+
+	/**
+	 * Create a new {@link RestartClassLoader} instance.
+	 * @param parent the parent classloader
+	 * @param updatedFiles any files that have been updated since the JARs referenced in
+	 * URLs were created.
 	 * @param urls the urls managed by the classloader
 	 * @param logger the logger used for messages
 	 */
-	public RestartClassLoader(ClassLoader parent, URL[] urls, Log logger) {
+	public RestartClassLoader(ClassLoader parent, URL[] urls,
+			ClassLoaderFileRepository updatedFiles, Log logger) {
 		super(urls, parent);
 		Assert.notNull(parent, "Parent must not be null");
+		Assert.notNull(updatedFiles, "UpdatedFiles must not be null");
 		Assert.notNull(logger, "Logger must not be null");
+		this.updatedFiles = updatedFiles;
 		this.logger = logger;
 		if (logger.isDebugEnabled()) {
 			logger.debug("Created RestartClassLoader " + toString());
@@ -66,11 +89,26 @@ public class RestartClassLoader extends URLClassLoader implements SmartClassLoad
 	@Override
 	public Enumeration<URL> getResources(String name) throws IOException {
 		// Use the parent since we're shadowing resource and we don't want duplicates
-		return getParent().getResources(name);
+		Enumeration<URL> resources = getParent().getResources(name);
+		ClassLoaderFile file = this.updatedFiles.getFile(name);
+		if (file != null) {
+			// Assume that we're replacing just the first item
+			if (resources.hasMoreElements()) {
+				resources.nextElement();
+			}
+			if (file.getKind() != Kind.DELETED) {
+				return new CompoundEnumeration<URL>(createFileUrl(name, file), resources);
+			}
+		}
+		return resources;
 	}
 
 	@Override
 	public URL getResource(String name) {
+		ClassLoaderFile file = this.updatedFiles.getFile(name);
+		if (file != null && file.getKind() == Kind.DELETED) {
+			return null;
+		}
 		URL resource = findResource(name);
 		if (resource != null) {
 			return resource;
@@ -78,8 +116,30 @@ public class RestartClassLoader extends URLClassLoader implements SmartClassLoad
 		return getParent().getResource(name);
 	}
 
+	@Override
+	public URL findResource(final String name) {
+		final ClassLoaderFile file = this.updatedFiles.getFile(name);
+		if (file == null) {
+			return super.findResource(name);
+		}
+		if (file.getKind() == Kind.DELETED) {
+			return null;
+		}
+		return AccessController.doPrivileged(new PrivilegedAction<URL>() {
+			@Override
+			public URL run() {
+				return createFileUrl(name, file);
+			}
+		});
+	}
+
 	@Override
 	public Class<?> loadClass(String name, boolean resolve) throws ClassNotFoundException {
+		String path = name.replace('.', '/').concat(".class");
+		ClassLoaderFile file = this.updatedFiles.getFile(path);
+		if (file != null && file.getKind() == Kind.DELETED) {
+			throw new ClassNotFoundException(name);
+		}
 		Class<?> loadedClass = findLoadedClass(name);
 		if (loadedClass == null) {
 			try {
@@ -95,6 +155,35 @@ public class RestartClassLoader extends URLClassLoader implements SmartClassLoad
 		return loadedClass;
 	}
 
+	@Override
+	protected Class<?> findClass(final String name) throws ClassNotFoundException {
+		String path = name.replace('.', '/').concat(".class");
+		final ClassLoaderFile file = this.updatedFiles.getFile(path);
+		if (file == null) {
+			return super.findClass(name);
+		}
+		if (file.getKind() == Kind.DELETED) {
+			throw new ClassNotFoundException(name);
+		}
+		return AccessController.doPrivileged(new PrivilegedAction<Class<?>>() {
+			@Override
+			public Class<?> run() {
+				byte[] bytes = file.getContents();
+				return defineClass(name, bytes, 0, bytes.length);
+			}
+		});
+	}
+
+	private URL createFileUrl(String name, ClassLoaderFile file) {
+		try {
+			return new URL("reloaded", null, -1, "/" + name,
+					new ClassLoaderFileURLStreamHandler(file));
+		}
+		catch (MalformedURLException ex) {
+			throw new IllegalStateException(ex);
+		}
+	}
+
 	@Override
 	protected void finalize() throws Throwable {
 		if (this.logger.isDebugEnabled()) {
@@ -108,4 +197,35 @@ public class RestartClassLoader extends URLClassLoader implements SmartClassLoad
 		return (classType.getClassLoader() instanceof RestartClassLoader);
 	}
 
+	/**
+	 * Compound {@link Enumeration} that adds an additional item to the front.
+	 */
+	private static class CompoundEnumeration<E> implements Enumeration<E> {
+
+		private E firstElement;
+
+		private final Enumeration<E> enumeration;
+
+		public CompoundEnumeration(E firstElement, Enumeration<E> enumeration) {
+			this.firstElement = firstElement;
+			this.enumeration = enumeration;
+		}
+
+		@Override
+		public boolean hasMoreElements() {
+			return (this.firstElement != null || this.enumeration.hasMoreElements());
+		}
+
+		@Override
+		public E nextElement() {
+			if (this.firstElement == null) {
+				return this.enumeration.nextElement();
+			}
+			E element = this.firstElement;
+			this.firstElement = null;
+			return element;
+		}
+
+	}
+
 }

spring-boot-developer-tools/src/test/java/org/springframework/boot/developertools/restart/RestarterTests.java

@@ -18,6 +18,8 @@ package org.springframework.boot.developertools.restart;
 
 import java.net.URL;
 import java.net.URLClassLoader;
+import java.util.Collection;
+import java.util.Collections;
 import java.util.concurrent.ThreadFactory;
 
 import org.junit.After;
@@ -27,11 +29,15 @@ import org.junit.Test;
 import org.junit.rules.ExpectedException;
 import org.springframework.beans.BeansException;
 import org.springframework.beans.factory.ObjectFactory;
+import org.springframework.boot.developertools.restart.classloader.ClassLoaderFile;
+import org.springframework.boot.developertools.restart.classloader.ClassLoaderFile.Kind;
+import org.springframework.boot.developertools.restart.classloader.ClassLoaderFiles;
 import org.springframework.boot.test.OutputCapture;
 import org.springframework.context.annotation.AnnotationConfigApplicationContext;
 import org.springframework.scheduling.annotation.EnableScheduling;
 import org.springframework.scheduling.annotation.Scheduled;
 import org.springframework.stereotype.Component;
+import org.springframework.util.FileCopyUtils;
 import org.springframework.util.StringUtils;
 
 import static org.hamcrest.Matchers.equalTo;
@@ -100,6 +106,44 @@ public class RestarterTests {
 		assertThat(attribute, equalTo((Object) "abc"));
 	}
 
+	public void addUrlsMustNotBeNull() throws Exception {
+		this.thrown.expect(IllegalArgumentException.class);
+		this.thrown.expectMessage("Urls must not be null");
+		Restarter.getInstance().addUrls(null);
+	}
+
+	@Test
+	public void addUrls() throws Exception {
+		URL url = new URL("file:/proj/module-a.jar!/");
+		Collection<URL> urls = Collections.singleton(url);
+		Restarter restarter = Restarter.getInstance();
+		restarter.addUrls(urls);
+		restarter.restart();
+		ClassLoader classLoader = ((TestableRestarter) restarter)
+				.getRelaunchClassLoader();
+		assertThat(((URLClassLoader) classLoader).getURLs()[0], equalTo(url));
+	}
+
+	@Test
+	public void addClassLoaderFilesMustNotBeNull() throws Exception {
+		this.thrown.expect(IllegalArgumentException.class);
+		this.thrown.expectMessage("ClassLoaderFiles must not be null");
+		Restarter.getInstance().addClassLoaderFiles(null);
+	}
+
+	@Test
+	public void addClassLoaderFiles() throws Exception {
+		ClassLoaderFiles classLoaderFiles = new ClassLoaderFiles();
+		classLoaderFiles.addFile("f", new ClassLoaderFile(Kind.ADDED, "abc".getBytes()));
+		Restarter restarter = Restarter.getInstance();
+		restarter.addClassLoaderFiles(classLoaderFiles);
+		restarter.restart();
+		ClassLoader classLoader = ((TestableRestarter) restarter)
+				.getRelaunchClassLoader();
+		assertThat(FileCopyUtils.copyToByteArray(classLoader.getResourceAsStream("f")),
+				equalTo("abc".getBytes()));
+	}
+
 	@Test
 	@SuppressWarnings("rawtypes")
 	public void getOrAddAttributeWithExistingAttribute() throws Exception {
@@ -191,6 +235,8 @@ public class RestarterTests {
 
 	private static class TestableRestarter extends Restarter {
 
+		private ClassLoader relaunchClassLoader;
+
 		public TestableRestarter() {
 			this(Thread.currentThread(), new String[] {}, false,
 					new MockRestartInitializer());
@@ -212,10 +258,19 @@ public class RestarterTests {
 			}
 		}
 
+		@Override
+		protected void relaunch(ClassLoader classLoader) throws Exception {
+			this.relaunchClassLoader = classLoader;
+		}
+
 		@Override
 		protected void stop() throws Exception {
 		}
 
+		public ClassLoader getRelaunchClassLoader() {
+			return this.relaunchClassLoader;
+		}
+
 	}
 
 }

spring-boot-developer-tools/src/test/java/org/springframework/boot/developertools/restart/classloader/ClassLoaderFileTests.java

@@ -0,0 +1,90 @@
+/*
+ * Copyright 2012-2015 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.
+ * You may obtain a copy of the License at
+ *
+ *      http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+package org.springframework.boot.developertools.restart.classloader;
+
+import org.junit.Rule;
+import org.junit.Test;
+import org.junit.rules.ExpectedException;
+import org.springframework.boot.developertools.restart.classloader.ClassLoaderFile;
+import org.springframework.boot.developertools.restart.classloader.ClassLoaderFile.Kind;
+
+import static org.hamcrest.Matchers.equalTo;
+import static org.hamcrest.Matchers.nullValue;
+import static org.junit.Assert.assertThat;
+
+/**
+ * Tests for {@link ClassLoaderFile}.
+ *
+ * @author Phillip Webb
+ */
+public class ClassLoaderFileTests {
+
+	public static final byte[] BYTES = "ABC".getBytes();
+
+	@Rule
+	public ExpectedException thrown = ExpectedException.none();
+
+	@Test
+	public void kindMustNotBeNull() {
+		this.thrown.expect(IllegalArgumentException.class);
+		this.thrown.expectMessage("Kind must not be null");
+		new ClassLoaderFile(null, null);
+	}
+
+	@Test
+	public void addedContentsMustNotBeNull() throws Exception {
+		this.thrown.expect(IllegalArgumentException.class);
+		this.thrown.expectMessage("Contents must not be null");
+		new ClassLoaderFile(Kind.ADDED, null);
+	}
+
+	@Test
+	public void modifiedContentsMustNotBeNull() throws Exception {
+		this.thrown.expect(IllegalArgumentException.class);
+		this.thrown.expectMessage("Contents must not be null");
+		new ClassLoaderFile(Kind.MODIFIED, null);
+	}
+
+	@Test
+	public void deletedContentsMustBeNull() throws Exception {
+		this.thrown.expect(IllegalArgumentException.class);
+		this.thrown.expectMessage("Contents must be null");
+		new ClassLoaderFile(Kind.DELETED, new byte[10]);
+	}
+
+	@Test
+	public void added() throws Exception {
+		ClassLoaderFile file = new ClassLoaderFile(Kind.ADDED, BYTES);
+		assertThat(file.getKind(), equalTo(ClassLoaderFile.Kind.ADDED));
+		assertThat(file.getContents(), equalTo(BYTES));
+	}
+
+	@Test
+	public void modified() throws Exception {
+		ClassLoaderFile file = new ClassLoaderFile(Kind.MODIFIED, BYTES);
+		assertThat(file.getKind(), equalTo(ClassLoaderFile.Kind.MODIFIED));
+		assertThat(file.getContents(), equalTo(BYTES));
+	}
+
+	@Test
+	public void deleted() throws Exception {
+		ClassLoaderFile file = new ClassLoaderFile(Kind.DELETED, null);
+		assertThat(file.getKind(), equalTo(ClassLoaderFile.Kind.DELETED));
+		assertThat(file.getContents(), nullValue());
+	}
+
+}

spring-boot-developer-tools/src/test/java/org/springframework/boot/developertools/restart/classloader/ClassLoaderFilesTests.java

@@ -0,0 +1,184 @@
+/*
+ * Copyright 2012-2015 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.
+ * You may obtain a copy of the License at
+ *
+ *      http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+package org.springframework.boot.developertools.restart.classloader;
+
+import java.io.ByteArrayInputStream;
+import java.io.ByteArrayOutputStream;
+import java.io.ObjectInputStream;
+import java.io.ObjectOutputStream;
+import java.util.ArrayList;
+import java.util.Arrays;
+import java.util.Iterator;
+
+import org.junit.Rule;
+import org.junit.Test;
+import org.junit.rules.ExpectedException;
+import org.springframework.boot.developertools.restart.classloader.ClassLoaderFile.Kind;
+import org.springframework.boot.developertools.restart.classloader.ClassLoaderFiles.SourceFolder;
+
+import static org.hamcrest.Matchers.equalTo;
+import static org.hamcrest.Matchers.notNullValue;
+import static org.hamcrest.Matchers.nullValue;
+import static org.junit.Assert.assertThat;
+import static org.mockito.Mockito.mock;
+
+/**
+ * Tests for {@link ClassLoaderFiles}.
+ *
+ * @author Phillip Webb
+ */
+public class ClassLoaderFilesTests {
+
+	@Rule
+	public ExpectedException thrown = ExpectedException.none();
+
+	private ClassLoaderFiles files = new ClassLoaderFiles();
+
+	@Test
+	public void addFileNameMustNotBeNull() throws Exception {
+		this.thrown.expect(IllegalArgumentException.class);
+		this.thrown.expectMessage("Name must not be null");
+		this.files.addFile(null, mock(ClassLoaderFile.class));
+	}
+
+	@Test
+	public void addFileFileMustNotBeNull() throws Exception {
+		this.thrown.expect(IllegalArgumentException.class);
+		this.thrown.expectMessage("File must not be null");
+		this.files.addFile("test", null);
+	}
+
+	@Test
+	public void getFileWithNullName() throws Exception {
+		assertThat(this.files.getFile(null), nullValue());
+	}
+
+	@Test
+	public void addAndGet() throws Exception {
+		ClassLoaderFile file = new ClassLoaderFile(Kind.ADDED, new byte[10]);
+		this.files.addFile("myfile", file);
+		assertThat(this.files.getFile("myfile"), equalTo(file));
+	}
+
+	@Test
+	public void getMissing() throws Exception {
+		assertThat(this.files.getFile("missing"), nullValue());
+	}
+
+	@Test
+	public void addTwice() throws Exception {
+		ClassLoaderFile file1 = new ClassLoaderFile(Kind.ADDED, new byte[10]);
+		ClassLoaderFile file2 = new ClassLoaderFile(Kind.MODIFIED, new byte[10]);
+		this.files.addFile("myfile", file1);
+		this.files.addFile("myfile", file2);
+		assertThat(this.files.getFile("myfile"), equalTo(file2));
+	}
+
+	@Test
+	public void addTwiceInDifferentSourceFolders() throws Exception {
+		ClassLoaderFile file1 = new ClassLoaderFile(Kind.ADDED, new byte[10]);
+		ClassLoaderFile file2 = new ClassLoaderFile(Kind.MODIFIED, new byte[10]);
+		this.files.addFile("a", "myfile", file1);
+		this.files.addFile("b", "myfile", file2);
+		assertThat(this.files.getFile("myfile"), equalTo(file2));
+		assertThat(this.files.getOrCreateSourceFolder("a").getFiles().size(), equalTo(0));
+		assertThat(this.files.getOrCreateSourceFolder("b").getFiles().size(), equalTo(1));
+	}
+
+	@Test
+	public void getSourceFolders() throws Exception {
+		ClassLoaderFile file1 = new ClassLoaderFile(Kind.ADDED, new byte[10]);
+		ClassLoaderFile file2 = new ClassLoaderFile(Kind.MODIFIED, new byte[10]);
+		ClassLoaderFile file3 = new ClassLoaderFile(Kind.MODIFIED, new byte[10]);
+		ClassLoaderFile file4 = new ClassLoaderFile(Kind.MODIFIED, new byte[10]);
+		this.files.addFile("a", "myfile1", file1);
+		this.files.addFile("a", "myfile2", file2);
+		this.files.addFile("b", "myfile3", file3);
+		this.files.addFile("b", "myfile4", file4);
+		Iterator<SourceFolder> sourceFolders = this.files.getSourceFolders().iterator();
+		SourceFolder sourceFolder1 = sourceFolders.next();
+		SourceFolder sourceFolder2 = sourceFolders.next();
+		assertThat(sourceFolders.hasNext(), equalTo(false));
+		assertThat(sourceFolder1.getName(), equalTo("a"));
+		assertThat(sourceFolder2.getName(), equalTo("b"));
+		assertThat(new ArrayList<ClassLoaderFile>(sourceFolder1.getFiles()),
+				equalTo(Arrays.asList(file1, file2)));
+		assertThat(new ArrayList<ClassLoaderFile>(sourceFolder2.getFiles()),
+				equalTo(Arrays.asList(file3, file4)));
+	}
+
+	@Test
+	public void serialzie() throws Exception {
+		ClassLoaderFile file = new ClassLoaderFile(Kind.ADDED, new byte[10]);
+		this.files.addFile("myfile", file);
+		ByteArrayOutputStream bos = new ByteArrayOutputStream();
+		ObjectOutputStream oos = new ObjectOutputStream(bos);
+		oos.writeObject(this.files);
+		oos.close();
+		ObjectInputStream ois = new ObjectInputStream(new ByteArrayInputStream(
+				bos.toByteArray()));
+		ClassLoaderFiles readObject = (ClassLoaderFiles) ois.readObject();
+		assertThat(readObject.getFile("myfile"), notNullValue());
+	}
+
+	@Test
+	public void addAll() throws Exception {
+		ClassLoaderFile file1 = new ClassLoaderFile(Kind.ADDED, new byte[10]);
+		this.files.addFile("a", "myfile1", file1);
+		ClassLoaderFiles toAdd = new ClassLoaderFiles();
+		ClassLoaderFile file2 = new ClassLoaderFile(Kind.MODIFIED, new byte[10]);
+		ClassLoaderFile file3 = new ClassLoaderFile(Kind.MODIFIED, new byte[10]);
+		toAdd.addFile("a", "myfile2", file2);
+		toAdd.addFile("b", "myfile3", file3);
+		this.files.addAll(toAdd);
+		Iterator<SourceFolder> sourceFolders = this.files.getSourceFolders().iterator();
+		SourceFolder sourceFolder1 = sourceFolders.next();
+		SourceFolder sourceFolder2 = sourceFolders.next();
+		assertThat(sourceFolders.hasNext(), equalTo(false));
+		assertThat(sourceFolder1.getName(), equalTo("a"));
+		assertThat(sourceFolder2.getName(), equalTo("b"));
+		assertThat(new ArrayList<ClassLoaderFile>(sourceFolder1.getFiles()),
+				equalTo(Arrays.asList(file1, file2)));
+	}
+
+	@Test
+	public void getSize() throws Exception {
+		this.files.addFile("s1", "n1", mock(ClassLoaderFile.class));
+		this.files.addFile("s1", "n2", mock(ClassLoaderFile.class));
+		this.files.addFile("s2", "n3", mock(ClassLoaderFile.class));
+		this.files.addFile("s2", "n1", mock(ClassLoaderFile.class));
+		assertThat(this.files.size(), equalTo(3));
+	}
+
+	@Test
+	public void classLoaderFilesMustNotBeNull() throws Exception {
+		this.thrown.expect(IllegalArgumentException.class);
+		this.thrown.expectMessage("ClassLoaderFiles must not be null");
+		new ClassLoaderFiles(null);
+	}
+
+	@Test
+	public void constructFromExistingSet() throws Exception {
+		this.files.addFile("s1", "n1", mock(ClassLoaderFile.class));
+		this.files.addFile("s1", "n2", mock(ClassLoaderFile.class));
+		ClassLoaderFiles copy = new ClassLoaderFiles(this.files);
+		this.files.addFile("s2", "n3", mock(ClassLoaderFile.class));
+		assertThat(this.files.size(), equalTo(3));
+		assertThat(copy.size(), equalTo(2));
+	}
+
+}

spring-boot-developer-tools/src/test/java/org/springframework/boot/developertools/restart/classloader/RestartClassLoaderTests.java

@@ -34,6 +34,7 @@ import org.junit.Rule;
 import org.junit.Test;
 import org.junit.rules.ExpectedException;
 import org.junit.rules.TemporaryFolder;
+import org.springframework.boot.developertools.restart.classloader.ClassLoaderFile.Kind;
 import org.springframework.util.FileCopyUtils;
 import org.springframework.util.StreamUtils;
 
@@ -66,6 +67,8 @@ public class RestartClassLoaderTests {
 
 	private URLClassLoader parentClassLoader;
 
+	private ClassLoaderFiles updatedFiles;
+
 	private RestartClassLoader reloadClassLoader;
 
 	@Before
@@ -75,7 +78,9 @@ public class RestartClassLoaderTests {
 		ClassLoader classLoader = getClass().getClassLoader();
 		URL[] urls = new URL[] { url };
 		this.parentClassLoader = new URLClassLoader(urls, classLoader);
-		this.reloadClassLoader = new RestartClassLoader(this.parentClassLoader, urls);
+		this.updatedFiles = new ClassLoaderFiles();
+		this.reloadClassLoader = new RestartClassLoader(this.parentClassLoader, urls,
+				this.updatedFiles);
 	}
 
 	private File createSampleJarFile() throws IOException {
@@ -98,6 +103,13 @@ public class RestartClassLoaderTests {
 		new RestartClassLoader(null, new URL[] {});
 	}
 
+	@Test
+	public void updatedFilesMustNotBeNull() throws Exception {
+		this.thrown.expect(IllegalArgumentException.class);
+		this.thrown.expectMessage("UpdatedFiles must not be null");
+		new RestartClassLoader(this.parentClassLoader, new URL[] {}, null);
+	}
+
 	@Test
 	public void getResourceFromReloadableUrl() throws Exception {
 		String content = readString(this.reloadClassLoader
@@ -131,6 +143,73 @@ public class RestartClassLoaderTests {
 		assertThat(loaded.getClassLoader(), equalTo(getClass().getClassLoader()));
 	}
 
+	@Test
+	public void getDeletedResource() throws Exception {
+		String name = PACKAGE_PATH + "/Sample.txt";
+		this.updatedFiles.addFile(name, new ClassLoaderFile(Kind.DELETED, null));
+		assertThat(this.reloadClassLoader.getResource(name), equalTo(null));
+	}
+
+	@Test
+	public void getDeletedResourceAsStream() throws Exception {
+		String name = PACKAGE_PATH + "/Sample.txt";
+		this.updatedFiles.addFile(name, new ClassLoaderFile(Kind.DELETED, null));
+		assertThat(this.reloadClassLoader.getResourceAsStream(name), equalTo(null));
+	}
+
+	@Test
+	public void getUpdatedResource() throws Exception {
+		String name = PACKAGE_PATH + "/Sample.txt";
+		byte[] bytes = "abc".getBytes();
+		this.updatedFiles.addFile(name, new ClassLoaderFile(Kind.MODIFIED, bytes));
+		URL resource = this.reloadClassLoader.getResource(name);
+		assertThat(FileCopyUtils.copyToByteArray(resource.openStream()), equalTo(bytes));
+	}
+
+	@Test
+	public void getResourcesWithDeleted() throws Exception {
+		String name = PACKAGE_PATH + "/Sample.txt";
+		this.updatedFiles.addFile(name, new ClassLoaderFile(Kind.DELETED, null));
+		List<URL> resources = toList(this.reloadClassLoader.getResources(name));
+		assertThat(resources.size(), equalTo(0));
+	}
+
+	@Test
+	public void getResourcesWithUpdated() throws Exception {
+		String name = PACKAGE_PATH + "/Sample.txt";
+		byte[] bytes = "abc".getBytes();
+		this.updatedFiles.addFile(name, new ClassLoaderFile(Kind.MODIFIED, bytes));
+		List<URL> resources = toList(this.reloadClassLoader.getResources(name));
+		assertThat(FileCopyUtils.copyToByteArray(resources.get(0).openStream()),
+				equalTo(bytes));
+	}
+
+	@Test
+	public void getDeletedClass() throws Exception {
+		String name = PACKAGE_PATH + "/Sample.class";
+		this.updatedFiles.addFile(name, new ClassLoaderFile(Kind.DELETED, null));
+		this.thrown.expect(ClassNotFoundException.class);
+		this.reloadClassLoader.loadClass(PACKAGE + ".Sample");
+	}
+
+	@Test
+	public void getUpdatedClass() throws Exception {
+		String name = PACKAGE_PATH + "/Sample.class";
+		this.updatedFiles.addFile(name, new ClassLoaderFile(Kind.MODIFIED, new byte[10]));
+		this.thrown.expect(ClassFormatError.class);
+		this.reloadClassLoader.loadClass(PACKAGE + ".Sample");
+	}
+
+	@Test
+	public void getAddedClass() throws Exception {
+		String name = PACKAGE_PATH + "/SampleParent.class";
+		byte[] bytes = FileCopyUtils.copyToByteArray(getClass().getResourceAsStream(
+				"SampleParent.class"));
+		this.updatedFiles.addFile(name, new ClassLoaderFile(Kind.ADDED, bytes));
+		Class<?> loaded = this.reloadClassLoader.loadClass(PACKAGE + ".SampleParent");
+		assertThat(loaded.getClassLoader(), equalTo((ClassLoader) this.reloadClassLoader));
+	}
+
 	private String readString(InputStream in) throws IOException {
 		return new String(FileCopyUtils.copyToByteArray(in));
 	}