Add support for unpacking nested JARs

Update the executable JAR code to automatically unpack any entries
which include an entry comment starting `UNPACK:` to the temp folder.
The existing Maven and Gradle plugins have been updated with new
configuration options and the `spring-boot-tools` project has been
updated to write the appropriate entry comment based on a flag passed
in via the `Library` class.

This support has been added to allow libraries such a JRuby (which
assumes that `jruby-complete.jar` is always accessible as file) to work
with Spring Boot executable jars.

Fixes gh-1070

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

@@ -17,7 +17,10 @@
 package org.springframework.boot.loader.archive;
 
 import java.io.File;
+import java.io.FileOutputStream;
 import java.io.IOException;
+import java.io.InputStream;
+import java.io.OutputStream;
 import java.net.MalformedURLException;
 import java.net.URL;
 import java.util.ArrayList;
@@ -27,6 +30,7 @@ import java.util.List;
 import java.util.jar.JarEntry;
 import java.util.jar.Manifest;
 
+import org.springframework.boot.loader.data.RandomAccessData.ResourceAccess;
 import org.springframework.boot.loader.jar.JarEntryData;
 import org.springframework.boot.loader.jar.JarEntryFilter;
 import org.springframework.boot.loader.jar.JarFile;
@@ -39,12 +43,23 @@ import org.springframework.boot.loader.util.AsciiBytes;
  */
 public class JarFileArchive extends Archive {
 
+	private static final AsciiBytes UNPACK_MARKER = new AsciiBytes("UNPACK:");
+
+	private static final int BUFFER_SIZE = 32 * 1024;
+
 	private final JarFile jarFile;
 
 	private final List<Entry> entries;
 
+	private URL url;
+
 	public JarFileArchive(File file) throws IOException {
+		this(file, null);
+	}
+
+	public JarFileArchive(File file, URL url) throws IOException {
 		this(new JarFile(file));
+		this.url = url;
 	}
 
 	public JarFileArchive(JarFile jarFile) {
@@ -58,6 +73,9 @@ public class JarFileArchive extends Archive {
 
 	@Override
 	public URL getUrl() throws MalformedURLException {
+		if (this.url != null) {
+			return this.url;
+		}
 		return this.jarFile.getUrl();
 	}
 
@@ -84,10 +102,54 @@ public class JarFileArchive extends Archive {
 
 	protected Archive getNestedArchive(Entry entry) throws IOException {
 		JarEntryData data = ((JarFileEntry) entry).getJarEntryData();
+		if (data.getComment().startsWith(UNPACK_MARKER)) {
+			return getUnpackedNestedArchive(data);
+		}
 		JarFile jarFile = this.jarFile.getNestedJarFile(data);
 		return new JarFileArchive(jarFile);
 	}
 
+	private Archive getUnpackedNestedArchive(JarEntryData data) throws IOException {
+		AsciiBytes hash = data.getComment().substring(UNPACK_MARKER.length());
+		String name = data.getName().toString();
+		if (name.lastIndexOf("/") != -1) {
+			name = name.substring(name.lastIndexOf("/") + 1);
+		}
+		File file = new File(getTempUnpackFolder(), hash.toString() + "-" + name);
+		if (!file.exists() || file.length() != data.getSize()) {
+			unpack(data, file);
+		}
+		return new JarFileArchive(file, file.toURI().toURL());
+	}
+
+	private File getTempUnpackFolder() {
+		File tempFolder = new File(System.getProperty("java.io.tmpdir"));
+		File unpackFolder = new File(tempFolder, "spring-boot-libs");
+		unpackFolder.mkdirs();
+		return unpackFolder;
+	}
+
+	private void unpack(JarEntryData data, File file) throws IOException {
+		InputStream inputStream = data.getData().getInputStream(ResourceAccess.ONCE);
+		try {
+			OutputStream outputStream = new FileOutputStream(file);
+			try {
+				byte[] buffer = new byte[BUFFER_SIZE];
+				int bytesRead = -1;
+				while ((bytesRead = inputStream.read(buffer)) != -1) {
+					outputStream.write(buffer, 0, bytesRead);
+				}
+				outputStream.flush();
+			}
+			finally {
+				outputStream.close();
+			}
+		}
+		finally {
+			inputStream.close();
+		}
+	}
+
 	@Override
 	public Archive getFilteredArchive(final EntryRenameFilter filter) throws IOException {
 		JarFile filteredJar = this.jarFile.getFilteredJarFile(new JarEntryFilter() {

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

@@ -96,10 +96,11 @@ public class Handler extends URLStreamHandler {
 			return openConnection(getFallbackHandler(), url);
 		}
 		catch (Exception ex) {
-			this.logger.log(Level.WARNING, "Unable to open fallback handler", ex);
 			if (reason instanceof IOException) {
+				this.logger.log(Level.FINEST, "Unable to open fallback handler", ex);
 				throw (IOException) reason;
 			}
+			this.logger.log(Level.WARNING, "Unable to open fallback handler", ex);
 			if (reason instanceof RuntimeException) {
 				throw (RuntimeException) reason;
 			}
@@ -111,7 +112,6 @@ public class Handler extends URLStreamHandler {
 		if (this.fallbackHandler != null) {
 			return this.fallbackHandler;
 		}
-
 		for (String handlerClassName : FALLBACK_HANDLERS) {
 			try {
 				Class<?> handlerClass = Class.forName(handlerClassName);

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

@@ -93,7 +93,13 @@ public final class JarEntryData {
 		return inputStream;
 	}
 
-	RandomAccessData getData() throws IOException {
+	/**
+	 * @return the underlying {@link RandomAccessData} for this entry. Generally this
+	 * method should not be called directly and instead data should be accessed via
+	 * {@link JarFile#getInputStream(ZipEntry)}.
+	 * @throws IOException
+	 */
+	public RandomAccessData getData() throws IOException {
 		if (this.data == null) {
 			// aspectjrt-1.7.4.jar has a different ext bytes length in the
 			// local directory to the central directory. We need to re-read

spring-boot-tools/spring-boot-loader/src/test/java/org/springframework/boot/loader/TestJarCreator.java

@@ -35,6 +35,10 @@ import java.util.zip.ZipEntry;
 public abstract class TestJarCreator {
 
 	public static void createTestJar(File file) throws Exception {
+		createTestJar(file, false);
+	}
+
+	public static void createTestJar(File file, boolean unpackNested) throws Exception {
 		FileOutputStream fileOutputStream = new FileOutputStream(file);
 		JarOutputStream jarOutputStream = new JarOutputStream(fileOutputStream);
 		try {
@@ -50,6 +54,9 @@ public abstract class TestJarCreator {
 			byte[] nestedJarData = getNestedJarData();
 			nestedEntry.setSize(nestedJarData.length);
 			nestedEntry.setCompressedSize(nestedJarData.length);
+			if (unpackNested) {
+				nestedEntry.setComment("UNPACK:0000000000000000000000000000000000000000");
+			}
 			CRC32 crc32 = new CRC32();
 			crc32.update(nestedJarData);
 			nestedEntry.setCrc(crc32.getValue());

spring-boot-tools/spring-boot-loader/src/test/java/org/springframework/boot/loader/archive/JarFileArchiveTests.java

@@ -29,7 +29,9 @@ import org.springframework.boot.loader.TestJarCreator;
 import org.springframework.boot.loader.archive.Archive.Entry;
 import org.springframework.boot.loader.util.AsciiBytes;
 
+import static org.hamcrest.Matchers.endsWith;
 import static org.hamcrest.Matchers.equalTo;
+import static org.hamcrest.Matchers.startsWith;
 import static org.junit.Assert.assertThat;
 
 /**
@@ -48,8 +50,12 @@ public class JarFileArchiveTests {
 
 	@Before
 	public void setup() throws Exception {
+		setup(false);
+	}
+
+	private void setup(boolean unpackNested) throws Exception {
 		this.rootJarFile = this.temporaryFolder.newFile();
-		TestJarCreator.createTestJar(this.rootJarFile);
+		TestJarCreator.createTestJar(this.rootJarFile, unpackNested);
 		this.archive = new JarFileArchive(this.rootJarFile);
 	}
 
@@ -80,6 +86,15 @@ public class JarFileArchiveTests {
 				equalTo("jar:file:" + this.rootJarFile.getPath() + "!/nested.jar!/"));
 	}
 
+	@Test
+	public void getNestedUnpackedArchive() throws Exception {
+		setup(true);
+		Entry entry = getEntriesMap(this.archive).get("nested.jar");
+		Archive nested = this.archive.getNestedArchive(entry);
+		assertThat(nested.getUrl().toString(), startsWith("file:"));
+		assertThat(nested.getUrl().toString(), endsWith(".jar"));
+	}
+
 	@Test
 	public void getFilteredArchive() throws Exception {
 		Archive filteredArchive = this.archive