Support custom fat jar layouts

Allow support for custom Lyout implementations with both the Maven
and Gradle plugin. Implementations of `LayoutFactory` can now be
specified to allow customization of the layout. In addition a
layout may now implement `CustomLoaderLayout` if it wishes to
write custom loader classes.

See spring-projectsgh-7263

spring-boot-docs/src/main/asciidoc/build-tool-plugins.adoc

@@ -484,6 +484,11 @@ The following configuration options are available:
  (defaults to a guess based on the archive type). See
  <<build-tool-plugins-gradle-configuration-layouts,available layouts for more details>>.
 
+|'layoutFactory`
+|A layout factory that can be used if a custom layout is required. Alternative layouts
+can be provided by 3rd parties. Layout factories are only used when `layout` is not
+specified.
+
 |`requiresUnpack`
 |A list of dependencies (in the form "`groupId:artifactId`" that must be unpacked from
  fat jars in order to run. Items are still packaged into the fat jar, but they will be
@@ -530,6 +535,38 @@ loader should be included or not. The following layouts are available:
 
 
 
++[[build-tool-plugins-gradle-configuration-custom-repackager]]
++==== Using a custom layout
+If you have custom requirements for how to arrange the dependencies and loader classes
+inside the repackaged jar, you can use a custom layout. Any library which defines one
+or more `LayoutFactory` implementations can be added to the build script dependencies
+and then the layout factory becomes available in the `springBoot` configuration.
+For example:
+
+[source,groovy,indent=0,subs="verbatim,attributes"]
+----
+buildscript {
+	repositories {
+		mavenCentral()
+	}
+	dependencies {
+		classpath("org.springframework.boot:spring-boot-gradle-plugin:{spring-boot-version}")
+		classpath("com.example:custom-layout:1.0.0")
+	}
+}
+
+springBoot {
+    layoutFactory = new com.example.CustomLayoutFactory()
+}
++----
+
+NOTE: If there is only one custom `LayoutFactory` on the build classpath and it is
+listed in `META-INF/spring.factories` then it is unnecessary to explicitly set it in the
+`springBoot` configuration. Layout factories are only used when no explicit `layout` is
+specified.
+
+
+
 [[build-tool-plugins-understanding-the-gradle-plugin]]
 === Understanding how the Gradle plugin works
 When `spring-boot` is applied to your Gradle project a default task named `bootRepackage`

spring-boot-tools/spring-boot-gradle-plugin/src/main/java/org/springframework/boot/gradle/SpringBootPluginExtension.java

@@ -26,6 +26,7 @@
 
 import org.springframework.boot.gradle.buildinfo.BuildInfo;
 import org.springframework.boot.loader.tools.Layout;
+import org.springframework.boot.loader.tools.LayoutFactory;
 import org.springframework.boot.loader.tools.Layouts;
 
 /**
@@ -90,6 +91,12 @@ public class SpringBootPluginExtension {
 	 */
 	LayoutType layout;
 
+	/**
+	 * The layout factory that will be used when no explicit layout is specified.
+	 * Alternative layouts can be provided by 3rd parties.
+	 */
+	LayoutFactory layoutFactory;
+
 	/**
 	 * Libraries that must be unpacked from fat jars in order to run. Use Strings in the
 	 * form {@literal groupId:artifactId}.
@@ -196,6 +203,14 @@ public void setLayout(LayoutType layout) {
 		this.layout = layout;
 	}
 
+	public LayoutFactory getLayoutFactory() {
+		return this.layoutFactory;
+	}
+
+	public void setLayoutFactory(LayoutFactory layoutFactory) {
+		this.layoutFactory = layoutFactory;
+	}
+
 	public Set<String> getRequiresUnpack() {
 		return this.requiresUnpack;
 	}

spring-boot-tools/spring-boot-gradle-plugin/src/main/java/org/springframework/boot/gradle/repackage/RepackageTask.java

@@ -213,7 +213,8 @@ private void repackage(File file) {
 				copy(file, outputFile);
 				file = outputFile;
 			}
-			Repackager repackager = new Repackager(file);
+			Repackager repackager = new Repackager(file,
+					this.extension.getLayoutFactory());
 			repackager.addMainClassTimeoutWarningListener(
 					new LoggingMainClassTimeoutWarningListener());
 			setMainClass(repackager);

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

@@ -0,0 +1,37 @@
+/*
+ * Copyright 2012-2016 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.loader.tools;
+
+import java.io.IOException;
+
+/**
+ * Additional interface that can be implemented by {@link Layout Layouts} that write their
+ * own loader classes.
+ *
+ * @author Phillip Webb
+ * @since 1.5.0
+ */
+public interface CustomLoaderLayout {
+
+	/**
+	 * Write the required loader classes into the JAR.
+	 * @param writer the writer used to write the classes
+	 * @throws IOException if the classes cannot be written
+	 */
+	void writeLoadedClasses(LoaderClassesWriter writer) throws IOException;
+
+}

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

@@ -0,0 +1,34 @@
+/*
+ * Copyright 2012-2016 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.loader.tools;
+
+import java.io.File;
+
+/**
+ * Default implementation of {@link LayoutFactory}.
+ *
+ * @author Phillip Webb
+ * @since 1.5.0
+ */
+public class DefaultLayoutFactory implements LayoutFactory {
+
+	@Override
+	public Layout getLayout(File source) {
+		return Layouts.forFile(source);
+	}
+
+}

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

@@ -51,7 +51,7 @@
  * @author Phillip Webb
  * @author Andy Wilkinson
  */
-public class JarWriter {
+public class JarWriter implements LoaderClassesWriter {
 
 	private static final String NESTED_LOADER_JAR = "META-INF/loader/spring-boot-loader.jar";
 
@@ -158,6 +158,7 @@ void writeEntries(JarFile jarFile, EntryTransformer entryTransformer)
 	 * @param inputStream The stream from which the entry's data can be read
 	 * @throws IOException if the write fails
 	 */
+	@Override
 	public void writeEntry(String entryName, InputStream inputStream) throws IOException {
 		JarEntry entry = new JarEntry(entryName);
 		writeEntry(entry, new InputStreamEntryWriter(inputStream, true));
@@ -207,8 +208,20 @@ private long getNestedLibraryTime(File file) {
 	 * Write the required spring-boot-loader classes to the JAR.
 	 * @throws IOException if the classes cannot be written
 	 */
+	@Override
 	public void writeLoaderClasses() throws IOException {
-		URL loaderJar = getClass().getClassLoader().getResource(NESTED_LOADER_JAR);
+		writeLoaderClasses(NESTED_LOADER_JAR);
+	}
+
+	/**
+	 * Write the required spring-boot-loader classes to the JAR.
+	 * @param loaderJarResourceName the name of the resource containing the loader classes
+	 * to be written
+	 * @throws IOException if the classes cannot be written
+	 */
+	@Override
+	public void writeLoaderClasses(String loaderJarResourceName) throws IOException {
+		URL loaderJar = getClass().getClassLoader().getResource(loaderJarResourceName);
 		JarInputStream inputStream = new JarInputStream(
 				new BufferedInputStream(loaderJar.openStream()));
 		JarEntry entry;

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

@@ -18,9 +18,13 @@
 
 /**
  * Strategy interface used to determine the layout for a particular type of archive.
+ * Layouts may additionally implement {@link CustomLoaderLayout} if they wish to write
+ * custom loader classes.
  *
  * @author Phillip Webb
  * @see Layouts
+ * @see RepackagingLayout
+ * @see CustomLoaderLayout
  */
 public interface Layout {
 

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

@@ -0,0 +1,36 @@
+/*
+ * Copyright 2012-2016 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.loader.tools;
+
+import java.io.File;
+
+/**
+ * Factory interface used to create a {@link Layout}.
+ *
+ * @author Dave Syer
+ * @author Phillip Webb
+ */
+public interface LayoutFactory {
+
+	/**
+	 * Return a {@link Layout} for the specified source file.
+	 * @param source the source file
+	 * @return the layout to use for the file
+	 */
+	Layout getLayout(File source);
+
+}

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

@@ -0,0 +1,53 @@
+/*
+ * Copyright 2012-2016 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.loader.tools;
+
+import java.io.IOException;
+import java.io.InputStream;
+
+/**
+ * Writer used by {@link CustomLoaderLayout CustomLoaderLayouts} to write classes into a
+ * repackaged JAR.
+ *
+ * @author Phillip Webb
+ * @since 1.5.0
+ */
+public interface LoaderClassesWriter {
+
+	/**
+	 * Write the default required spring-boot-loader classes to the JAR.
+	 * @throws IOException if the classes cannot be written
+	 */
+	void writeLoaderClasses() throws IOException;
+
+	/**
+	 * Write custom required spring-boot-loader classes to the JAR.
+	 * @param loaderJarResourceName the name of the resource containing the loader classes
+	 * to be written
+	 * @throws IOException if the classes cannot be written
+	 */
+	void writeLoaderClasses(String loaderJarResourceName) throws IOException;
+
+	/**
+	 * Write a single entry to the JAR.
+	 * @param name the name of the entry
+	 * @param inputStream the input stream content
+	 * @throws IOException if the entry cannot be written
+	 */
+	void writeEntry(String name, InputStream inputStream) throws IOException;
+
+}