Add a parent last classloader for restart use

Add a parent last classloader for use with application restarts. The
classloader provides a layer on top of the regular classloader to
contain the classes that might change when an application is restarted.

See gh-3084

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

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+/*
+ * 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.IOException;
+import java.net.URL;
+import java.net.URLClassLoader;
+import java.util.Enumeration;
+
+import org.apache.commons.logging.Log;
+import org.apache.commons.logging.LogFactory;
+import org.springframework.core.SmartClassLoader;
+import org.springframework.util.Assert;
+
+/**
+ * Disposable {@link ClassLoader} used to support application restarting. Provides parent
+ * last loading for the specified URLs.
+ *
+ * @author Andy Clement
+ * @author Phillip Webb
+ * @since 1.3.0
+ */
+public class RestartClassLoader extends URLClassLoader implements SmartClassLoader {
+
+	private final Log logger;
+
+	/**
+	 * Create a new {@link RestartClassLoader} instance.
+	 * @param parent the parent classloader URLs were created.
+	 * @param urls the urls managed by the classloader
+	 */
+	public RestartClassLoader(ClassLoader parent, URL[] urls) {
+		this(parent, urls, LogFactory.getLog(RestartClassLoader.class));
+	}
+
+	/**
+	 * Create a new {@link RestartClassLoader} instance.
+	 * @param parent the parent classloader 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) {
+		super(urls, parent);
+		Assert.notNull(parent, "Parent must not be null");
+		Assert.notNull(logger, "Logger must not be null");
+		this.logger = logger;
+		if (logger.isDebugEnabled()) {
+			logger.debug("Created RestartClassLoader " + toString());
+		}
+	}
+
+	@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);
+	}
+
+	@Override
+	public URL getResource(String name) {
+		URL resource = findResource(name);
+		if (resource != null) {
+			return resource;
+		}
+		return getParent().getResource(name);
+	}
+
+	@Override
+	public Class<?> loadClass(String name, boolean resolve) throws ClassNotFoundException {
+		Class<?> loadedClass = findLoadedClass(name);
+		if (loadedClass == null) {
+			try {
+				loadedClass = findClass(name);
+			}
+			catch (ClassNotFoundException ex) {
+				loadedClass = getParent().loadClass(name);
+			}
+		}
+		if (resolve) {
+			resolveClass(loadedClass);
+		}
+		return loadedClass;
+	}
+
+	@Override
+	protected void finalize() throws Throwable {
+		if (this.logger.isDebugEnabled()) {
+			this.logger.debug("Finalized classloader " + toString());
+		}
+		super.finalize();
+	}
+
+	@Override
+	public boolean isClassReloadable(Class<?> classType) {
+		return (classType.getClassLoader() instanceof RestartClassLoader);
+	}
+
+}

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

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+/*
+ * 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.
+ */
+
+/**
+ * Classloaders used for reload support
+ */
+package org.springframework.boot.developertools.restart.classloader;
+

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

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+/*
+ * 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.File;
+import java.io.FileOutputStream;
+import java.io.IOException;
+import java.io.InputStream;
+import java.net.URL;
+import java.net.URLClassLoader;
+import java.nio.charset.Charset;
+import java.util.ArrayList;
+import java.util.Enumeration;
+import java.util.List;
+import java.util.jar.JarOutputStream;
+import java.util.zip.ZipEntry;
+
+import org.junit.Before;
+import org.junit.Rule;
+import org.junit.Test;
+import org.junit.rules.ExpectedException;
+import org.junit.rules.TemporaryFolder;
+import org.springframework.util.FileCopyUtils;
+import org.springframework.util.StreamUtils;
+
+import static org.hamcrest.Matchers.equalTo;
+import static org.hamcrest.Matchers.startsWith;
+import static org.junit.Assert.assertThat;
+
+/**
+ * Tests for {@link RestartClassLoader}.
+ *
+ * @author Phillip Webb
+ */
+@SuppressWarnings("resource")
+public class RestartClassLoaderTests {
+
+	private static final String PACKAGE = RestartClassLoaderTests.class.getPackage()
+			.getName();
+
+	private static final String PACKAGE_PATH = PACKAGE.replace(".", "/");
+
+	private static final Charset UTF_8 = Charset.forName("UTF-8");
+
+	@Rule
+	public ExpectedException thrown = ExpectedException.none();
+
+	@Rule
+	public TemporaryFolder temp = new TemporaryFolder();
+
+	private File sampleJarFile;
+
+	private URLClassLoader parentClassLoader;
+
+	private RestartClassLoader reloadClassLoader;
+
+	@Before
+	public void setup() throws Exception {
+		this.sampleJarFile = createSampleJarFile();
+		URL url = this.sampleJarFile.toURI().toURL();
+		ClassLoader classLoader = getClass().getClassLoader();
+		URL[] urls = new URL[] { url };
+		this.parentClassLoader = new URLClassLoader(urls, classLoader);
+		this.reloadClassLoader = new RestartClassLoader(this.parentClassLoader, urls);
+	}
+
+	private File createSampleJarFile() throws IOException {
+		File file = this.temp.newFile("sample.jar");
+		JarOutputStream jarOutputStream = new JarOutputStream(new FileOutputStream(file));
+		jarOutputStream.putNextEntry(new ZipEntry(PACKAGE_PATH + "/Sample.class"));
+		StreamUtils.copy(getClass().getResourceAsStream("Sample.class"), jarOutputStream);
+		jarOutputStream.closeEntry();
+		jarOutputStream.putNextEntry(new ZipEntry(PACKAGE_PATH + "/Sample.txt"));
+		StreamUtils.copy("fromchild", UTF_8, jarOutputStream);
+		jarOutputStream.closeEntry();
+		jarOutputStream.close();
+		return file;
+	}
+
+	@Test
+	public void parentMustNotBeNull() throws Exception {
+		this.thrown.expect(IllegalArgumentException.class);
+		this.thrown.expectMessage("Parent must not be null");
+		new RestartClassLoader(null, new URL[] {});
+	}
+
+	@Test
+	public void getResourceFromReloadableUrl() throws Exception {
+		String content = readString(this.reloadClassLoader
+				.getResourceAsStream(PACKAGE_PATH + "/Sample.txt"));
+		assertThat(content, startsWith("fromchild"));
+	}
+
+	@Test
+	public void getResourceFromParent() throws Exception {
+		String content = readString(this.reloadClassLoader
+				.getResourceAsStream(PACKAGE_PATH + "/Parent.txt"));
+		assertThat(content, startsWith("fromparent"));
+	}
+
+	@Test
+	public void getResourcesFiltersDuplicates() throws Exception {
+		List<URL> resources = toList(this.reloadClassLoader.getResources(PACKAGE_PATH
+				+ "/Sample.txt"));
+		assertThat(resources.size(), equalTo(1));
+	}
+
+	@Test
+	public void loadClassFromReloadableUrl() throws Exception {
+		Class<?> loaded = this.reloadClassLoader.loadClass(PACKAGE + ".Sample");
+		assertThat(loaded.getClassLoader(), equalTo((ClassLoader) this.reloadClassLoader));
+	}
+
+	@Test
+	public void loadClassFromParent() throws Exception {
+		Class<?> loaded = this.reloadClassLoader.loadClass(PACKAGE + ".SampleParent");
+		assertThat(loaded.getClassLoader(), equalTo(getClass().getClassLoader()));
+	}
+
+	private String readString(InputStream in) throws IOException {
+		return new String(FileCopyUtils.copyToByteArray(in));
+	}
+
+	private <T> List<T> toList(Enumeration<T> enumeration) {
+		List<T> list = new ArrayList<T>();
+		if (enumeration != null) {
+			while (enumeration.hasMoreElements()) {
+				list.add(enumeration.nextElement());
+			}
+		}
+		return list;
+	}
+
+}

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

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+/*
+ * 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 sample class used to test reloading.
+ *
+ * @author Phillip Webb
+ */
+public class Sample {
+
+}

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

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+/*
+ * 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 sample class used to test reloading.
+ *
+ * @author Phillip Webb
+ */
+public class SampleParent {
+
+}