Do not include empty starter jars in fat jars

Closes spring-projectsgh-22036

buildSrc/src/main/java/org/springframework/boot/build/starters/StarterPlugin.java

@@ -17,6 +17,8 @@
 package org.springframework.boot.build.starters;
 
 import java.io.File;
+import java.util.Map;
+import java.util.TreeMap;
 
 import org.gradle.api.Plugin;
 import org.gradle.api.Project;
@@ -26,6 +28,7 @@
 import org.gradle.api.plugins.JavaLibraryPlugin;
 import org.gradle.api.plugins.JavaPlugin;
 import org.gradle.api.plugins.PluginContainer;
+import org.gradle.api.tasks.bundling.Jar;
 
 import org.springframework.boot.build.ConventionsPlugin;
 import org.springframework.boot.build.DeployedPlugin;
@@ -57,6 +60,7 @@ public void apply(Project project) {
 				(artifact) -> artifact.builtBy(starterMetadata));
 		createClasspathConflictsCheck(runtimeClasspath, project);
 		createProhibitedDependenciesCheck(runtimeClasspath, project);
+		configureJarManifest(project);
 	}
 
 	private void createClasspathConflictsCheck(Configuration classpath, Project project) {
@@ -75,4 +79,14 @@ private void createProhibitedDependenciesCheck(Configuration classpath, Project
 		project.getTasks().getByName(JavaBasePlugin.CHECK_TASK_NAME).dependsOn(checkClasspathForProhibitedDependencies);
 	}
 
+	private void configureJarManifest(Project project) {
+		project.getTasks().withType(Jar.class, (jar) -> project.afterEvaluate((evaluated) -> {
+			jar.manifest((manifest) -> {
+				Map<String, Object> attributes = new TreeMap<>();
+				attributes.put("Spring-Boot-Starter", project.getName());
+				manifest.attributes(attributes);
+			});
+		}));
+	}
+
 }

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

@@ -30,6 +30,7 @@
 import java.util.Map;
 import java.util.Set;
 import java.util.function.Function;
+import java.util.regex.Pattern;
 import java.util.stream.Collectors;
 import java.util.zip.CRC32;
 
@@ -49,6 +50,7 @@
 
 import org.springframework.boot.loader.tools.DefaultLaunchScript;
 import org.springframework.boot.loader.tools.FileUtils;
+import org.springframework.boot.loader.tools.JarFileUtils;
 import org.springframework.boot.loader.tools.JarModeLibrary;
 import org.springframework.boot.loader.tools.Layer;
 import org.springframework.boot.loader.tools.LayersIndex;
@@ -67,6 +69,8 @@
  */
 class BootZipCopyAction implements CopyAction {
 
+	static final Pattern SPRING_BOOT_STARTER_JAR_PATTERN = Pattern.compile("spring-boot-starter-.*\\.jar");
+
 	static final long CONSTANT_TIME_FOR_ZIP_ENTRIES = new GregorianCalendar(1980, Calendar.FEBRUARY, 1, 0, 0, 0)
 			.getTimeInMillis();
 
@@ -232,6 +236,9 @@ private void processDirectory(FileCopyDetails details) throws IOException {
 		}
 
 		private void processFile(FileCopyDetails details) throws IOException {
+			if (isSpringBootStarterJar(details)) {
+				return;
+			}
 			String name = details.getRelativePath().getPathString();
 			ZipArchiveEntry entry = new ZipArchiveEntry(name);
 			prepareEntry(entry, name, getTime(details), UnixStat.FILE_FLAG | details.getMode());
@@ -251,6 +258,13 @@ private void processFile(FileCopyDetails details) throws IOException {
 			}
 		}
 
+		private boolean isSpringBootStarterJar(FileCopyDetails details) {
+			if (SPRING_BOOT_STARTER_JAR_PATTERN.matcher(details.getSourceName()).matches()) {
+				return JarFileUtils.hasManifestAttribute(details.getFile(), "Spring-Boot-Starter");
+			}
+			return false;
+		}
+
 		private void writeParentDirectoriesIfNecessary(String name, Long time) throws IOException {
 			String parentDirectory = getParentDirectory(name);
 			if (parentDirectory != null && this.writtenDirectories.add(parentDirectory)) {

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

@@ -30,6 +30,7 @@
 import java.util.List;
 import java.util.Map;
 import java.util.Set;
+import java.util.jar.Attributes;
 import java.util.jar.JarEntry;
 import java.util.jar.JarFile;
 import java.util.jar.JarOutputStream;
@@ -369,6 +370,17 @@ void devtoolsJarIsExcludedByDefault() throws IOException {
 		}
 	}
 
+	@Test
+	void springBootStarterJarIsExcluded() throws IOException {
+		this.task.setMainClassName("com.example.Main");
+		this.task.classpath(springBootJarFile("spring-boot-starter-web-0.1.2.jar"));
+		executeTask();
+		assertThat(this.task.getArchiveFile().get().getAsFile()).exists();
+		try (JarFile jarFile = new JarFile(this.task.getArchiveFile().get().getAsFile())) {
+			assertThat(jarFile.getEntry(this.libPath + "spring-boot-starter-web-0.1.2.jar")).isNull();
+		}
+	}
+
 	@Test
 	@Deprecated
 	void devtoolsJarCanBeIncluded() throws IOException {
@@ -430,6 +442,20 @@ protected File jarFile(String name) throws IOException {
 		return file;
 	}
 
+	protected File springBootJarFile(String name) throws IOException {
+		File file = newFile(name);
+		try (JarOutputStream jar = new JarOutputStream(new FileOutputStream(file))) {
+			jar.putNextEntry(new ZipEntry("META-INF/MANIFEST.MF"));
+			Manifest manifest = new Manifest();
+			Attributes attributes = manifest.getMainAttributes();
+			attributes.put(Attributes.Name.MANIFEST_VERSION, "1.0");
+			attributes.putValue("Spring-Boot-Starter", name);
+			manifest.write(jar);
+			jar.closeEntry();
+		}
+		return file;
+	}
+
 	private T configure(T task) throws IOException {
 		AbstractArchiveTask archiveTask = task;
 		archiveTask.getArchiveBaseName().set("test");

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

@@ -0,0 +1,47 @@
+/*
+ * 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.loader.tools;
+
+import java.io.File;
+import java.util.jar.Attributes;
+import java.util.jar.JarFile;
+
+/**
+ * Utilities for working with {@link java.util.jar.JarFile}.
+ *
+ * @author Christoph Dreis
+ * @since 2.4.0
+ */
+public abstract class JarFileUtils {
+
+	/**
+	 * Determines if a file has an attribute in the JARs manifest.
+	 * @param file the jar file
+	 * @param attribute name of the attribute
+	 * @return {@code true} if attribute with the given name was found in the JAR
+	 * manifest, {@code false} otherwise
+	 */
+	public static boolean hasManifestAttribute(File file, String attribute) {
+		try (JarFile jarFile = new JarFile(file)) {
+			return jarFile.getManifest().getMainAttributes().containsKey(new Attributes.Name(attribute));
+		}
+		catch (Exception ignore) {
+		}
+		return false;
+	}
+
+}

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

@@ -28,6 +28,7 @@
 import java.util.jar.Attributes;
 import java.util.jar.JarFile;
 import java.util.jar.Manifest;
+import java.util.regex.Pattern;
 import java.util.stream.Collectors;
 import java.util.zip.ZipEntry;
 
@@ -70,6 +71,8 @@ public abstract class Packager {
 
 	private static final String SPRING_BOOT_APPLICATION_CLASS_NAME = "org.springframework.boot.autoconfigure.SpringBootApplication";
 
+	private static final Pattern SPRING_BOOT_STARTER_JAR_PATTERN = Pattern.compile("spring-boot-starter-.*\\.jar");
+
 	private List<MainClassTimeoutWarningListener> mainClassTimeoutListeners = new ArrayList<>();
 
 	private String mainClass;
@@ -461,7 +464,7 @@ private final class WritableLibraries implements UnpackHandler {
 
 		WritableLibraries(Libraries libraries) throws IOException {
 			libraries.doWithLibraries((library) -> {
-				if (isZip(library::openStream)) {
+				if (isZip(library::openStream) && !isSpringBootStarterJar(library)) {
 					addLibrary(library);
 				}
 			});
@@ -479,6 +482,13 @@ private void addLibrary(Library library) {
 			}
 		}
 
+		private boolean isSpringBootStarterJar(Library library) {
+			if (SPRING_BOOT_STARTER_JAR_PATTERN.matcher(library.getName()).matches()) {
+				return JarFileUtils.hasManifestAttribute(library.getFile(), "Spring-Boot-Starter");
+			}
+			return false;
+		}
+
 		@Override
 		public boolean requiresUnpack(String name) {
 			Library library = this.libraries.get(name);

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

@@ -32,6 +32,7 @@
 import java.util.Random;
 import java.util.Set;
 import java.util.jar.Attributes;
+import java.util.jar.JarOutputStream;
 import java.util.jar.Manifest;
 import java.util.stream.Collectors;
 import java.util.stream.Stream;
@@ -583,12 +584,41 @@ void kotlinModuleMetadataMovesBeneathBootInfClassesWhenRepackaged() throws Excep
 		assertThat(getPackagedEntry("BOOT-INF/classes/META-INF/test.kotlin_module")).isNotNull();
 	}
 
+	@Test
+	void springBootStarterJarIsExcluded() throws IOException {
+		this.testJarFile.addClass("com/example/Application.class", ClassWithMainMethod.class);
+		File libraryOne = createSpringBootJarFile("spring-boot-starter-web-0.1.2.jar");
+		P packager = createPackager();
+		execute(packager, (callback) -> callback.library(new Library(libraryOne, LibraryScope.COMPILE, false)));
+		assertThat(getPackagedEntryNames()).doesNotContain("BOOT-INF/lib/" + libraryOne.getName());
+	}
+
 	private File createLibrary() throws IOException {
 		TestJarFile library = new TestJarFile(this.tempDir);
 		library.addClass("com/example/library/Library.class", ClassWithoutMainMethod.class);
 		return library.getFile();
 	}
 
+	protected File createSpringBootJarFile(String name) throws IOException {
+		File file = newFile(name);
+		try (JarOutputStream jar = new JarOutputStream(new FileOutputStream(file))) {
+			jar.putNextEntry(new ZipEntry("META-INF/MANIFEST.MF"));
+			Manifest manifest = new Manifest();
+			Attributes attributes = manifest.getMainAttributes();
+			attributes.put(Attributes.Name.MANIFEST_VERSION, "1.0");
+			attributes.putValue("Spring-Boot-Starter", name);
+			manifest.write(jar);
+			jar.closeEntry();
+		}
+		return file;
+	}
+
+	protected File newFile(String name) throws IOException {
+		File file = new File(this.tempDir, name);
+		file.createNewFile();
+		return file;
+	}
+
 	protected final P createPackager() throws IOException {
 		return createPackager(this.testJarFile.getFile());
 	}