Allow users to opt out of including the layer tools in a layered jar

For Maven, the layer configuration is now an additional configuration
option instead of a layout type.

Closes gh-19866

spring-boot-project/spring-boot-tools/spring-boot-gradle-plugin/src/docs/asciidoc/packaging.adoc

@@ -287,3 +287,18 @@ The jar will then be split into layer folders which may include:
 * `snapshots-dependencies`
 * `dependencies`
 
+When you create a layered jar, the `spring-boot-layertools` jar will be added as a dependency to your jar.
+With this jar on the classpath, you can launch your application in a special mode which allows the bootstrap code to run something entirely different from your application, for example, something that extracts the layers.
+If you wish to exclude this dependency, you can do so in the following manner:
+
+[source,groovy,indent=0,subs="verbatim,attributes",role="primary"]
+.Groovy
+----
+include::../gradle/packaging/boot-jar-layered-exclude-tools.gradle[tags=layered]
+----
+
+[source,kotlin,indent=0,subs="verbatim,attributes",role="secondary"]
+.Kotlin
+----
+include::../gradle/packaging/boot-jar-layered-exclude-tools.gradle.kts[tags=layered]
+----

spring-boot-project/spring-boot-tools/spring-boot-gradle-plugin/src/docs/gradle/packaging/boot-jar-layered-exclude-tools.gradle

@@ -0,0 +1,16 @@
+plugins {
+	id 'java'
+	id 'org.springframework.boot' version '{version}'
+}
+
+bootJar {
+	mainClassName 'com.example.ExampleApplication'
+}
+
+// tag::layered[]
+bootJar {
+	layered {
+		includeLayerTools = false
+	}
+}
+// end::layered[]

spring-boot-project/spring-boot-tools/spring-boot-gradle-plugin/src/docs/gradle/packaging/boot-jar-layered-exclude-tools.gradle.kts

@@ -0,0 +1,18 @@
+import org.springframework.boot.gradle.tasks.bundling.BootJar
+
+plugins {
+	java
+	id("org.springframework.boot") version "{version}"
+}
+
+tasks.getByName<BootJar>("bootJar") {
+	mainClassName = "com.example.ExampleApplication"
+}
+
+// tag::layered[]
+tasks.getByName<BootJar>("bootJar") {
+	layered {
+		includeLayerTools = false
+	}
+}
+// end::layered[]

spring-boot-project/spring-boot-tools/spring-boot-gradle-plugin/src/main/java/org/springframework/boot/gradle/tasks/bundling/BootJar.java

@@ -40,6 +40,8 @@ import org.gradle.api.java.archives.Attributes;
 import org.gradle.api.specs.Spec;
 import org.gradle.api.tasks.Input;
 import org.gradle.api.tasks.Internal;
+import org.gradle.api.tasks.Nested;
+import org.gradle.api.tasks.Optional;
 import org.gradle.api.tasks.bundling.Jar;
 
 import org.springframework.boot.loader.tools.Layer;
@@ -67,6 +69,8 @@ public class BootJar extends Jar implements BootArchive {
 
 	private Layers layers;
 
+	private LayerConfiguration layerConfiguration;
+
 	private static final String BOOT_INF_LAYERS = "BOOT-INF/layers";
 
 	private final List<String> dependencies = new ArrayList<>();
@@ -164,20 +168,33 @@ public class BootJar extends Jar implements BootArchive {
 		action.execute(enableLaunchScriptIfNecessary());
 	}
 
+	@Optional
+	@Nested
+	@Input
+	public LayerConfiguration getLayerConfiguration() {
+		return this.layerConfiguration;
+	}
+
 	/**
 	 * Configures the archive to have layers.
 	 */
 	public void layered() {
-		this.layers = Layers.IMPLICIT;
-		this.bootInf.into("lib", (spec) -> spec.from((Callable<File>) () -> {
-			String jarName = "spring-boot-jarmode-layertools.jar";
-			InputStream stream = getClass().getClassLoader().getResourceAsStream("META-INF/jarmode/" + jarName);
-			File taskTmp = new File(getProject().getBuildDir(), "tmp/" + getName());
-			taskTmp.mkdirs();
-			File layerToolsJar = new File(taskTmp, jarName);
-			FileCopyUtils.copy(stream, new FileOutputStream(layerToolsJar));
-			return layerToolsJar;
-		}));
+		enableLayers();
+		applyLayers();
+	}
+
+	private void applyLayers() {
+		if (this.layerConfiguration.isIncludeLayerTools()) {
+			this.bootInf.into("lib", (spec) -> spec.from((Callable<File>) () -> {
+				String jarName = "spring-boot-jarmode-layertools.jar";
+				InputStream stream = getClass().getClassLoader().getResourceAsStream("META-INF/jarmode/" + jarName);
+				File taskTmp = new File(getProject().getBuildDir(), "tmp/" + getName());
+				taskTmp.mkdirs();
+				File layerToolsJar = new File(taskTmp, jarName);
+				FileCopyUtils.copy(stream, new FileOutputStream(layerToolsJar));
+				return layerToolsJar;
+			}));
+		}
 		this.bootInf.eachFile((details) -> {
 			Layer layer = layerForFileDetails(details);
 			if (layer != null) {
@@ -188,6 +205,20 @@ public class BootJar extends Jar implements BootArchive {
 		this.bootInf.into("", (spec) -> spec.from(createLayersIndex()));
 	}
 
+	public void layered(Action<LayerConfiguration> action) {
+		action.execute(enableLayers());
+		applyLayers();
+	}
+
+	private LayerConfiguration enableLayers() {
+		this.layers = Layers.IMPLICIT;
+		if (this.layerConfiguration == null) {
+			this.layerConfiguration = new LayerConfiguration();
+		}
+
+		return this.layerConfiguration;
+	}
+
 	private Layer layerForFileDetails(FileCopyDetails details) {
 		String path = details.getPath();
 		if (path.startsWith("BOOT-INF/lib/")) {

spring-boot-project/spring-boot-tools/spring-boot-gradle-plugin/src/main/java/org/springframework/boot/gradle/tasks/bundling/LayerConfiguration.java

@@ -0,0 +1,44 @@
+/*
+ * Copyright 2012-2020 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
+ *
+ *      https://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.gradle.tasks.bundling;
+
+import org.gradle.api.tasks.Input;
+
+/**
+ * Encapsulates the configuration for a layered jar.
+ *
+ * @author Madhura Bhave
+ * @since 2.3.0
+ */
+public class LayerConfiguration {
+
+	private boolean includeLayerTools = true;
+
+	/**
+	 * Whether to include the layer tools jar.
+	 * @return true if layer tools is included
+	 */
+	@Input
+	public boolean isIncludeLayerTools() {
+		return this.includeLayerTools;
+	}
+
+	public void setIncludeLayerTools(boolean includeLayerTools) {
+		this.includeLayerTools = includeLayerTools;
+	}
+
+}

spring-boot-project/spring-boot-tools/spring-boot-gradle-plugin/src/test/java/org/springframework/boot/gradle/tasks/bundling/BootJarIntegrationTests.java

@@ -29,6 +29,7 @@ import static org.assertj.core.api.Assertions.assertThat;
  * Integration tests for {@link BootJar}.
  *
  * @author Andy Wilkinson
+ * @author Madhura Bhave
  */
 class BootJarIntegrationTests extends AbstractBootArchiveIntegrationTests {
 
@@ -53,4 +54,13 @@ class BootJarIntegrationTests extends AbstractBootArchiveIntegrationTests {
 				.isEqualTo(TaskOutcome.SUCCESS);
 	}
 
+	@TestTemplate
+	void notUpToDateWhenBuiltWithLayersAndToolsAndThenWithLayersAndWithoutTools()
+			throws InvalidRunnerConfigurationException, UnexpectedBuildFailure, IOException {
+		assertThat(this.gradleBuild.build("-Playered=true", "bootJar").task(":bootJar").getOutcome())
+				.isEqualTo(TaskOutcome.SUCCESS);
+		assertThat(this.gradleBuild.build("-Playered=true", "-PexcludeTools=true", "bootJar").task(":bootJar")
+				.getOutcome()).isEqualTo(TaskOutcome.SUCCESS);
+	}
+
 }

spring-boot-project/spring-boot-tools/spring-boot-gradle-plugin/src/test/java/org/springframework/boot/gradle/tasks/bundling/BootJarTests.java

@@ -25,6 +25,7 @@ import java.util.jar.JarFile;
 import java.util.stream.Collectors;
 import java.util.zip.ZipEntry;
 
+import org.gradle.api.Action;
 import org.junit.jupiter.api.Test;
 
 import static org.assertj.core.api.Assertions.assertThat;
@@ -129,6 +130,13 @@ class BootJarTests extends AbstractBootArchiveTests<BootJar> {
 		assertThat(entryNames).contains("BOOT-INF/layers/dependencies/lib/spring-boot-jarmode-layertools.jar");
 	}
 
+	@Test
+	void whenJarIsLayeredAndIncludeLayerToolsIsFalseThenLayerToolsAreNotAddedToTheJar() throws IOException {
+		List<String> entryNames = getEntryNames(
+				createLayeredJar((configuration) -> configuration.setIncludeLayerTools(false)));
+		assertThat(entryNames).doesNotContain("BOOT-INF/layers/dependencies/lib/spring-boot-jarmode-layertools.jar");
+	}
+
 	@Test
 	void classpathIndexPointsToBootInfLibs() throws IOException {
 		try (JarFile jarFile = new JarFile(createPopulatedJar())) {
@@ -145,13 +153,22 @@ class BootJarTests extends AbstractBootArchiveTests<BootJar> {
 		return getTask().getArchiveFile().get().getAsFile();
 	}
 
-	private File createLayeredJar() throws IOException {
+	private File createLayeredJar(Action<LayerConfiguration> action) throws IOException {
 		addContent();
-		getTask().layered();
+		if (action != null) {
+			getTask().layered(action);
+		}
+		else {
+			getTask().layered();
+		}
 		executeTask();
 		return getTask().getArchiveFile().get().getAsFile();
 	}
 
+	private File createLayeredJar() throws IOException {
+		return createLayeredJar(null);
+	}
+
 	private void addContent() throws IOException {
 		BootJar bootJar = getTask();
 		bootJar.setMainClassName("com.example.Main");

spring-boot-project/spring-boot-tools/spring-boot-gradle-plugin/src/test/resources/org/springframework/boot/gradle/tasks/bundling/BootJarIntegrationTests.gradle

@@ -11,6 +11,8 @@ bootJar {
 		}
 	}
 	if (project.hasProperty('layered') && project.getProperty('layered')) {
-		layered()
+		layered {
+			includeLayerTools = project.hasProperty('excludeTools') && project.getProperty('excludeTools') ? false : true
+		}
 	}
 }