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-tools/src/main/java/org/springframework/boot/loader/tools/FileUtils.java

@@ -17,13 +17,19 @@
 package org.springframework.boot.loader.tools;
 
 import java.io.File;
+import java.io.FileInputStream;
+import java.io.IOException;
+import java.security.DigestInputStream;
+import java.security.MessageDigest;
+import java.security.NoSuchAlgorithmException;
 
 /**
  * Utilities for manipulating files and directories in Spring Boot tooling.
  * 
  * @author Dave Syer
+ * @author Phillip Webb
  */
-public class FileUtils {
+public abstract class FileUtils {
 
 	/**
 	 * Utility to remove duplicate files from an "output" directory if they already exist
@@ -50,4 +56,37 @@ public class FileUtils {
 		}
 	}
 
+	/**
+	 * Generate a SHA.1 Hash for a given file.
+	 * @param file the file to hash
+	 * @return the hash value as a String
+	 * @throws IOException
+	 */
+	public static String sha1Hash(File file) throws IOException {
+		try {
+			DigestInputStream inputStream = new DigestInputStream(new FileInputStream(
+					file), MessageDigest.getInstance("SHA-1"));
+			try {
+				byte[] buffer = new byte[4098];
+				while (inputStream.read(buffer) != -1) {
+					// Read the entire stream
+				}
+				return bytesToHex(inputStream.getMessageDigest().digest());
+			}
+			finally {
+				inputStream.close();
+			}
+		}
+		catch (NoSuchAlgorithmException ex) {
+			throw new IllegalStateException(ex);
+		}
+	}
+
+	private static String bytesToHex(byte[] bytes) {
+		StringBuilder hex = new StringBuilder();
+		for (byte b : bytes) {
+			hex.append(String.format("%02x", b));
+		}
+		return hex.toString();
+	}
 }

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

@@ -50,7 +50,7 @@ public class JarWriter {
 
 	private static final String NESTED_LOADER_JAR = "META-INF/loader/spring-boot-loader.jar";
 
-	private static final int BUFFER_SIZE = 4096;
+	private static final int BUFFER_SIZE = 32 * 1024;
 
 	private final JarOutputStream jarOutput;
 
@@ -122,11 +122,16 @@ public class JarWriter {
 	/**
 	 * Write a nested library.
 	 * @param destination the destination of the library
-	 * @param file the library file
+	 * @param library the library
 	 * @throws IOException if the write fails
 	 */
-	public void writeNestedLibrary(String destination, File file) throws IOException {
+	public void writeNestedLibrary(String destination, Library library)
+			throws IOException {
+		File file = library.getFile();
 		JarEntry entry = new JarEntry(destination + file.getName());
+		if (library.isUnpackRequired()) {
+			entry.setComment("UNPACK:" + FileUtils.sha1Hash(file));
+		}
 		new CrcAndSize(file).setupStoredEntry(entry);
 		writeEntry(entry, new InputStreamEntryWriter(new FileInputStream(file), true));
 	}

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

@@ -31,14 +31,27 @@ public class Library {
 
 	private final LibraryScope scope;
 
+	private final boolean unpackRequired;
+
 	/**
 	 * Create a new {@link Library}.
 	 * @param file the source file
 	 * @param scope the scope of the library
 	 */
 	public Library(File file, LibraryScope scope) {
+		this(file, scope, false);
+	}
+
+	/**
+	 * Create a new {@link Library}.
+	 * @param file the source file
+	 * @param scope the scope of the library
+	 * @param unpackRequired if the library needs to be unpacked before it can be used
+	 */
+	public Library(File file, LibraryScope scope, boolean unpackRequired) {
 		this.file = file;
 		this.scope = scope;
+		this.unpackRequired = unpackRequired;
 	}
 
 	/**
@@ -55,4 +68,12 @@ public class Library {
 		return this.scope;
 	}
 
+	/**
+	 * @return if the file cannot be used directly as a nested jar and needs to be
+	 * unpacked.
+	 */
+	public boolean isUnpackRequired() {
+		return this.unpackRequired;
+	}
+
 }

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

@@ -147,7 +147,7 @@ public class Repackager {
 						String destination = Repackager.this.layout
 								.getLibraryDestination(file.getName(), library.getScope());
 						if (destination != null) {
-							writer.writeNestedLibrary(destination, file);
+							writer.writeNestedLibrary(destination, library);
 						}
 					}
 				}