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 gh-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.gradle.api.plugins.JavaPlugin;
 
 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 class SpringBootPluginExtension {
 		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 @@ public class RepackageTask extends DefaultTask {
 				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 @@ import org.springframework.lang.UsesJava7;
  * @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 @@ public class JarWriter {
 	 * @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 @@ public class JarWriter {
 	 * 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 @@ package org.springframework.boot.loader.tools;
 
 /**
  * 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;
+
+}

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

@@ -30,7 +30,10 @@ import java.util.jar.JarFile;
 import java.util.jar.Manifest;
 
 import org.springframework.boot.loader.tools.JarWriter.EntryTransformer;
+import org.springframework.core.io.support.SpringFactoriesLoader;
 import org.springframework.lang.UsesJava8;
+import org.springframework.util.Assert;
+import org.springframework.util.StringUtils;
 
 /**
  * Utility class that can be used to repackage an archive so that it can be executed using
@@ -66,12 +69,18 @@ public class Repackager {
 
 	private Layout layout;
 
+	private LayoutFactory layoutFactory;
+
 	public Repackager(File source) {
+		this(source, null);
+	}
+
+	public Repackager(File source, LayoutFactory layoutFactory) {
 		if (source == null || !source.exists() || !source.isFile()) {
 			throw new IllegalArgumentException("Source must refer to an existing file");
 		}
 		this.source = source.getAbsoluteFile();
-		this.layout = Layouts.forFile(source);
+		this.layoutFactory = layoutFactory;
 	}
 
 	/**
@@ -113,6 +122,15 @@ public class Repackager {
 		this.layout = layout;
 	}
 
+	/**
+	 * Sets the layout factory for the jar. The factory can be used when no specific
+	 * layout is specific.
+	 * @param layoutFactory the layoutFactory to set
+	 */
+	public void setLayoutFactory(LayoutFactory layoutFactory) {
+		this.layoutFactory = layoutFactory;
+	}
+
 	/**
 	 * Repackage the source file so that it can be run using '{@literal java -jar}'.
 	 * @param libraries the libraries required to run the archive
@@ -150,6 +168,9 @@ public class Repackager {
 		if (libraries == null) {
 			throw new IllegalArgumentException("Libraries must not be null");
 		}
+		if (this.layout == null) {
+			this.layout = getLayoutFactory().getLayout(this.source);
+		}
 		if (alreadyRepackaged()) {
 			return;
 		}
@@ -177,6 +198,19 @@ public class Repackager {
 		}
 	}
 
+	private LayoutFactory getLayoutFactory() {
+		if (this.layoutFactory != null) {
+			return this.layoutFactory;
+		}
+		List<LayoutFactory> factories = SpringFactoriesLoader
+				.loadFactories(LayoutFactory.class, null);
+		if (factories.isEmpty()) {
+			return new DefaultLayoutFactory();
+		}
+		Assert.state(factories.size() == 1, "No unique LayoutFactory found");
+		return factories.get(0);
+	}
+
 	/**
 	 * Return the {@link File} to use to backup the original source.
 	 * @return the file to use to backup the original source
@@ -219,21 +253,7 @@ public class Repackager {
 				}
 
 			});
-			writer.writeManifest(buildManifest(sourceJar));
+			repackage(sourceJar, writer, unpackLibraries, standardLibraries);
-			Set<String> seen = new HashSet<String>();
-			writeNestedLibraries(unpackLibraries, seen, writer);
-			if (this.layout instanceof RepackagingLayout) {
-				writer.writeEntries(sourceJar,
-						new RenamingEntryTransformer(((RepackagingLayout) this.layout)
-								.getRepackagedClassesLocation()));
-			}
-			else {
-				writer.writeEntries(sourceJar);
-			}
-			writeNestedLibraries(standardLibraries, seen, writer);
-			if (this.layout.isExecutable()) {
-				writer.writeLoaderClasses();
-			}
 		}
 		finally {
 			try {
@@ -245,6 +265,23 @@ public class Repackager {
 		}
 	}
 
+	private void repackage(JarFile sourceJar, JarWriter writer,
+			final List<Library> unpackLibraries, final List<Library> standardLibraries)
+					throws IOException {
+		writer.writeManifest(buildManifest(sourceJar));
+		Set<String> seen = new HashSet<String>();
+		writeNestedLibraries(unpackLibraries, seen, writer);
+		if (this.layout instanceof RepackagingLayout) {
+			writer.writeEntries(sourceJar, new RenamingEntryTransformer(
+					((RepackagingLayout) this.layout).getRepackagedClassesLocation()));
+		}
+		else {
+			writer.writeEntries(sourceJar);
+		}
+		writeNestedLibraries(standardLibraries, seen, writer);
+		writeLoaderClasses(writer);
+	}
+
 	private void writeNestedLibraries(List<Library> libraries, Set<String> alreadySeen,
 			JarWriter writer) throws IOException {
 		for (Library library : libraries) {
@@ -260,6 +297,15 @@ public class Repackager {
 		}
 	}
 
+	private void writeLoaderClasses(JarWriter writer) throws IOException {
+		if (this.layout instanceof CustomLoaderLayout) {
+			((CustomLoaderLayout) this.layout).writeLoadedClasses(writer);
+		}
+		else if (this.layout.isExecutable()) {
+			writer.writeLoaderClasses();
+		}
+	}
+
 	private boolean isZip(File file) {
 		try {
 			FileInputStream fileInputStream = new FileInputStream(file);
@@ -316,8 +362,10 @@ public class Repackager {
 				(this.layout instanceof RepackagingLayout)
 						? ((RepackagingLayout) this.layout).getRepackagedClassesLocation()
 						: this.layout.getClassesLocation());
-		manifest.getMainAttributes().putValue(BOOT_LIB_ATTRIBUTE,
+		String lib = this.layout.getLibraryDestination("", LibraryScope.COMPILE);
-				this.layout.getLibraryDestination("", LibraryScope.COMPILE));
+		if (StringUtils.hasLength(lib)) {
+			manifest.getMainAttributes().putValue(BOOT_LIB_ATTRIBUTE, lib);
+		}
 		return manifest;
 	}
 

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

@@ -16,6 +16,7 @@
 
 package org.springframework.boot.loader.tools;
 
+import java.io.ByteArrayInputStream;
 import java.io.File;
 import java.io.IOException;
 import java.nio.file.Files;
@@ -347,14 +348,46 @@ public class RepackagerTests {
 		final LibraryScope scope = mock(LibraryScope.class);
 		given(layout.getLauncherClassName()).willReturn("testLauncher");
 		given(layout.getLibraryDestination(anyString(), eq(scope))).willReturn("test/");
+		given(layout.getLibraryDestination(anyString(), eq(LibraryScope.COMPILE)))
+				.willReturn("test-lib/");
 		repackager.setLayout(layout);
 		repackager.repackage(new Libraries() {
+
 			@Override
 			public void doWithLibraries(LibraryCallback callback) throws IOException {
 				callback.library(new Library(libJarFile, scope));
 			}
+
 		});
 		assertThat(hasEntry(file, "test/" + libJarFile.getName())).isTrue();
+		assertThat(getManifest(file).getMainAttributes().getValue("Spring-Boot-Lib"))
+				.isEqualTo("test-lib/");
+		assertThat(getManifest(file).getMainAttributes().getValue("Main-Class"))
+				.isEqualTo("testLauncher");
+	}
+
+	@Test
+	public void customLayoutNoBootLib() throws Exception {
+		TestJarFile libJar = new TestJarFile(this.temporaryFolder);
+		libJar.addClass("a/b/C.class", ClassWithoutMainMethod.class);
+		final File libJarFile = libJar.getFile();
+		this.testJarFile.addClass("a/b/C.class", ClassWithMainMethod.class);
+		File file = this.testJarFile.getFile();
+		Repackager repackager = new Repackager(file);
+		Layout layout = mock(Layout.class);
+		final LibraryScope scope = mock(LibraryScope.class);
+		given(layout.getLauncherClassName()).willReturn("testLauncher");
+		repackager.setLayout(layout);
+		repackager.repackage(new Libraries() {
+
+			@Override
+			public void doWithLibraries(LibraryCallback callback) throws IOException {
+				callback.library(new Library(libJarFile, scope));
+			}
+
+		});
+		assertThat(getManifest(file).getMainAttributes().getValue("Spring-Boot-Lib"))
+				.isNull();
 		assertThat(getManifest(file).getMainAttributes().getValue("Main-Class"))
 				.isEqualTo("testLauncher");
 	}
@@ -536,6 +569,29 @@ public class RepackagerTests {
 		}
 	}
 
+	@Test
+	public void customLayoutFactoryWithoutLayout() throws Exception {
+		this.testJarFile.addClass("a/b/C.class", ClassWithMainMethod.class);
+		File source = this.testJarFile.getFile();
+		Repackager repackager = new Repackager(source, new TestLayoutFactory());
+		repackager.repackage(NO_LIBRARIES);
+		JarFile jarFile = new JarFile(source);
+		assertThat(jarFile.getEntry("test")).isNotNull();
+		jarFile.close();
+	}
+
+	@Test
+	public void customLayoutFactoryWithLayout() throws Exception {
+		this.testJarFile.addClass("a/b/C.class", ClassWithMainMethod.class);
+		File source = this.testJarFile.getFile();
+		Repackager repackager = new Repackager(source, new TestLayoutFactory());
+		repackager.setLayout(new Layouts.Jar());
+		repackager.repackage(NO_LIBRARIES);
+		JarFile jarFile = new JarFile(source);
+		assertThat(jarFile.getEntry("test")).isNull();
+		jarFile.close();
+	}
+
 	private boolean hasLauncherClasses(File file) throws IOException {
 		return hasEntry(file, "org/springframework/boot/")
 				&& hasEntry(file, "org/springframework/boot/loader/JarLauncher.class");
@@ -580,4 +636,22 @@ public class RepackagerTests {
 
 	}
 
+	public static class TestLayoutFactory implements LayoutFactory {
+
+		@Override
+		public Layout getLayout(File source) {
+			return new TestLayout();
+		}
+
+	}
+
+	private static class TestLayout extends Layouts.Jar implements CustomLoaderLayout {
+
+		@Override
+		public void writeLoadedClasses(LoaderClassesWriter writer) throws IOException {
+			writer.writeEntry("test", new ByteArrayInputStream("test".getBytes()));
+		}
+
+	}
+
 }

spring-boot-tools/spring-boot-maven-plugin/src/main/java/org/springframework/boot/maven/RepackageMojo.java

@@ -40,6 +40,7 @@ import org.apache.maven.shared.artifact.filter.collection.ScopeFilter;
 import org.springframework.boot.loader.tools.DefaultLaunchScript;
 import org.springframework.boot.loader.tools.LaunchScript;
 import org.springframework.boot.loader.tools.Layout;
+import org.springframework.boot.loader.tools.LayoutFactory;
 import org.springframework.boot.loader.tools.Layouts;
 import org.springframework.boot.loader.tools.Libraries;
 import org.springframework.boot.loader.tools.Repackager;
@@ -129,6 +130,15 @@ public class RepackageMojo extends AbstractDependencyFilterMojo {
 	@Parameter
 	private LayoutType layout;
 
+	/**
+	 * The layout factory that will be used to create the executable archive if no
+	 * explicit layout is set. Alternative layouts implementations can be provided by 3rd
+	 * parties.
+	 * @since 1.5
+	 */
+	@Parameter
+	private LayoutFactory layoutFactory;
+
 	/**
 	 * A list of the libraries that must be unpacked from fat jars in order to run.
 	 * Specify each library as a <code>&lt;dependency&gt;</code> with a
@@ -220,7 +230,7 @@ public class RepackageMojo extends AbstractDependencyFilterMojo {
 	}
 
 	private Repackager getRepackager(File source) {
-		Repackager repackager = new Repackager(source);
+		Repackager repackager = new Repackager(source, this.layoutFactory);
 		repackager.addMainClassTimeoutWarningListener(
 				new LoggingMainClassTimeoutWarningListener());
 		repackager.setMainClass(this.mainClass);

spring-boot-tools/spring-boot-maven-plugin/src/site/apt/examples/custom-layout.apt

@@ -0,0 +1,58 @@
+ -----
+ Use a custom layout
+ -----
+ Dave Syer
+ -----
+ 2016-10-30
+ -----
+
+  Spring Boot repackages the jar file for this project using a custom layout factory
+  defined in the additional jar file, provided as a dependency to the build plugin:
+
+---
+<project>
+  ...
+  <build>
+    ...
+    <plugins>
+      ...
+      <plugin>
+        <groupId>${project.groupId}</groupId>
+        <artifactId>${project.artifactId}</artifactId>
+        <version>${project.version}</version>
+        <executions>
+          <execution>
+            <goals>
+              <goal>repackage</goal>
+            </goals>
+            <configuration>
+              <layoutFactory implementation="com.example.CustomLayoutFactory">
+                <customProperty>value</customProperty>
+              </layoutFactory>
+            </configuration>
+          </execution>
+        </executions>
+        <dependencies>
+          <dependency>
+            <groupId>com.example</groupid>
+            <artifactId>custom-layout</artifactId>
+            <version>0.0.1.BUILD-SNAPSHOT</version>
+          </dependency>
+        </dependencies>
+        ...
+      </plugin>
+      ...
+    </plugins>
+    ...
+  </build>
+  ...
+</project>
++---
+
+  The layout factory is provided as an implementation of <<<LayoutFactory>>> (from
+  spring-boot-loader-tools) explicitly specified in the pom. If there is only one custom
+  <<<LayoutFactory>>> on the plugin classpath and it is listed in
+  <<<META-INF/spring.factories>>> then it is unnecessary to explicitly set it in the
+  plugin configuration.
+
+  Layout factories are always ignored if an explicit <<layout>> is set.

spring-boot-tools/spring-boot-maven-plugin/src/site/apt/index.apt

@@ -48,6 +48,8 @@ Spring Boot Maven Plugin
 
   * {{{./examples/repackage-disable-attach.html}Local repackaged artifact}}
 
+* {{{./examples/custom-layout.html}Custom layout}}
+
   * {{{./examples/exclude-dependency.html}Exclude a dependency}}
 
   * {{{./examples/run-debug.html}Debug the application}}