Add support for layered jars in gradle plugin

Closes gh-19792

Co-authored-by: Andy Wilkinson <awilkinson@pivotal.io>

spring-boot-project/spring-boot-tools/spring-boot-gradle-plugin/src/test/java/org/springframework/boot/gradle/docs/PackagingDocumentationTests.java

@@ -178,6 +178,18 @@ class PackagingDocumentationTests {
 		assertThat(bootJar).isFile();
 	}
 
+	@TestTemplate
+	void bootJarLayered() throws IOException {
+		this.gradleBuild.script("src/docs/gradle/packaging/boot-jar-layered").build("bootJar");
+		File file = new File(this.gradleBuild.getProjectDir(),
+				"build/libs/" + this.gradleBuild.getProjectDir().getName() + ".jar");
+		assertThat(file).isFile();
+		try (JarFile jar = new JarFile(file)) {
+			JarEntry entry = jar.getJarEntry("BOOT-INF/layers.idx");
+			assertThat(entry).isNotNull();
+		}
+	}
+
 	protected void jarFile(File file) throws IOException {
 		try (JarOutputStream jar = new JarOutputStream(new FileOutputStream(file))) {
 			jar.putNextEntry(new ZipEntry("META-INF/MANIFEST.MF"));

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

@@ -1,5 +1,5 @@
 /*
- * Copyright 2012-2019 the original author or authors.
+ * 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.
@@ -16,6 +16,15 @@
 
 package org.springframework.boot.gradle.tasks.bundling;
 
+import java.io.IOException;
+
+import org.gradle.testkit.runner.InvalidRunnerConfigurationException;
+import org.gradle.testkit.runner.TaskOutcome;
+import org.gradle.testkit.runner.UnexpectedBuildFailure;
+import org.junit.jupiter.api.TestTemplate;
+
+import static org.assertj.core.api.Assertions.assertThat;
+
 /**
  * Integration tests for {@link BootJar}.
  *
@@ -27,4 +36,21 @@ class BootJarIntegrationTests extends AbstractBootArchiveIntegrationTests {
 		super("bootJar");
 	}
 
+	@TestTemplate
+	void upToDateWhenBuiltTwiceWithLayers()
+			throws InvalidRunnerConfigurationException, UnexpectedBuildFailure, IOException {
+		assertThat(this.gradleBuild.build("-Playered=true", "bootJar").task(":bootJar").getOutcome())
+				.isEqualTo(TaskOutcome.SUCCESS);
+		assertThat(this.gradleBuild.build("-Playered=true", "bootJar").task(":bootJar").getOutcome())
+				.isEqualTo(TaskOutcome.UP_TO_DATE);
+	}
+
+	@TestTemplate
+	void notUpToDateWhenBuiltWithoutLayersAndThenWithLayers()
+			throws InvalidRunnerConfigurationException, UnexpectedBuildFailure, IOException {
+		assertThat(this.gradleBuild.build("bootJar").task(":bootJar").getOutcome()).isEqualTo(TaskOutcome.SUCCESS);
+		assertThat(this.gradleBuild.build("-Playered=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

@@ -18,6 +18,8 @@ package org.springframework.boot.gradle.tasks.bundling;
 
 import java.io.File;
 import java.io.IOException;
+import java.io.InputStream;
+import java.util.List;
 import java.util.jar.JarFile;
 
 import org.junit.jupiter.api.Test;
@@ -28,6 +30,7 @@ import static org.assertj.core.api.Assertions.assertThat;
  * Tests for {@link BootJar}.
  *
  * @author Andy Wilkinson
+ * @author Madhura Bhave
  */
 class BootJarTests extends AbstractBootArchiveTests<BootJar> {
 
@@ -57,6 +60,48 @@ class BootJarTests extends AbstractBootArchiveTests<BootJar> {
 		}
 	}
 
+	@Test
+	void layers() throws IOException {
+		BootJar bootJar = getTask();
+		bootJar.setMainClassName("com.example.Main");
+		bootJar.layered();
+		File classesJavaMain = new File(this.temp, "classes/java/main");
+		File applicationClass = new File(classesJavaMain, "com/example/Application.class");
+		applicationClass.getParentFile().mkdirs();
+		applicationClass.createNewFile();
+		File resourcesMain = new File(this.temp, "resources/main");
+		File applicationProperties = new File(resourcesMain, "application.properties");
+		applicationProperties.getParentFile().mkdirs();
+		applicationProperties.createNewFile();
+		File staticResources = new File(resourcesMain, "static");
+		staticResources.mkdir();
+		File css = new File(staticResources, "test.css");
+		css.createNewFile();
+		bootJar.classpath(classesJavaMain, resourcesMain, jarFile("first-library.jar"), jarFile("second-library.jar"),
+				jarFile("third-library-SNAPSHOT.jar"));
+		bootJar.requiresUnpack("second-library.jar");
+		executeTask();
+		List<String> entryNames = getEntryNames(bootJar.getArchiveFile().get().getAsFile());
+		assertThat(entryNames).containsSubsequence("org/springframework/boot/loader/",
+				"BOOT-INF/layers/application/classes/com/example/Application.class",
+				"BOOT-INF/layers/resources/classes/static/test.css",
+				"BOOT-INF/layers/application/classes/application.properties",
+				"BOOT-INF/layers/dependencies/lib/first-library.jar",
+				"BOOT-INF/layers/dependencies/lib/second-library.jar",
+				"BOOT-INF/layers/snapshot-dependencies/lib/third-library-SNAPSHOT.jar");
+		assertThat(entryNames).doesNotContain("BOOT-INF/classes").doesNotContain("BOOT-INF/lib")
+				.doesNotContain("BOOT-INF/com/");
+		try (JarFile jarFile = new JarFile(bootJar.getArchiveFile().get().getAsFile())) {
+			assertThat(jarFile.getManifest().getMainAttributes().getValue("Spring-Boot-Classes")).isEqualTo(null);
+			assertThat(jarFile.getManifest().getMainAttributes().getValue("Spring-Boot-Lib")).isEqualTo(null);
+			assertThat(jarFile.getManifest().getMainAttributes().getValue("Spring-Boot-Layers-Index"))
+					.isEqualTo("BOOT-INF/layers.idx");
+			try (InputStream input = jarFile.getInputStream(jarFile.getEntry("BOOT-INF/layers.idx"))) {
+				assertThat(input).hasContent("dependencies\nsnapshot-dependencies\nresources\napplication\n");
+			}
+		}
+	}
+
 	@Override
 	protected void executeTask() {
 		getTask().copy();