Rename AutoConfigurationLoader to ImportCandidates

Move the class to a more suitable package, and load the files from
META-INF/spring/<fqn>.imports

See gh-29872

buildSrc/src/main/java/org/springframework/boot/build/autoconfigure/AutoConfigurationMetadata.java

@@ -66,7 +66,7 @@ public class AutoConfigurationMetadata extends DefaultTask {
 				.withPathSensitivity(PathSensitivity.RELATIVE).withPropertyName("spring.factories");
 		getInputs()
 				.file((Callable<File>) () -> new File(this.sourceSet.getOutput().getResourcesDir(),
-						"META-INF/spring-boot/org.springframework.boot.autoconfigure.AutoConfiguration"))
+						"META-INF/spring/org.springframework.boot.autoconfigure.AutoConfiguration.imports"))
 				.withPathSensitivity(PathSensitivity.RELATIVE)
 				.withPropertyName("org.springframework.boot.autoconfigure.AutoConfiguration");
 
@@ -137,17 +137,17 @@ public class AutoConfigurationMetadata extends DefaultTask {
 
 	/**
 	 * Reads auto-configurations from
-	 * META-INF/spring-boot/org.springframework.boot.autoconfigure.AutoConfiguration.
+	 * META-INF/spring/org.springframework.boot.autoconfigure.AutoConfiguration.imports.
 	 * @return auto-configurations
 	 */
 	private List<String> readAutoConfigurationsFile() throws IOException {
 		File file = new File(this.sourceSet.getOutput().getResourcesDir(),
-				"META-INF/spring-boot/org.springframework.boot.autoconfigure.AutoConfiguration");
+				"META-INF/spring/org.springframework.boot.autoconfigure.AutoConfiguration.imports");
 		if (!file.exists()) {
 			return Collections.emptyList();
 		}
 		// Nearly identical copy of
-		// org.springframework.boot.autoconfigure.AutoConfigurationLoader.readAutoConfigurations
+		// org.springframework.boot.context.annotation.ImportCandidates.load
 		try (BufferedReader reader = new BufferedReader(new InputStreamReader(new FileInputStream(file)))) {
 			List<String> autoConfigurations = new ArrayList<>();
 			String line;

buildSrc/src/main/java/org/springframework/boot/build/test/autoconfigure/TestSliceMetadata.java

@@ -106,7 +106,7 @@ public class TestSliceMetadata extends DefaultTask {
 			Properties springFactories = readSpringFactories(
 					new File(this.sourceSet.getOutput().getResourcesDir(), "META-INF/spring.factories"));
 			readTestSlicesDirectory(springFactories,
-					new File(this.sourceSet.getOutput().getResourcesDir(), "META-INF/spring-boot/"));
+					new File(this.sourceSet.getOutput().getResourcesDir(), "META-INF/spring/"));
 			for (File classesDir : this.sourceSet.getOutput().getClassesDirs()) {
 				addTestSlices(testSlices, classesDir, metadataReaderFactory, springFactories);
 			}
@@ -123,14 +123,17 @@ public class TestSliceMetadata extends DefaultTask {
 	 * @param directory directory to scan
 	 */
 	private void readTestSlicesDirectory(Properties springFactories, File directory) {
-		File[] files = directory.listFiles();
+		File[] files = directory.listFiles((dir, name) -> name.endsWith(".imports"));
 		if (files == null) {
 			return;
 		}
 		for (File file : files) {
 			try {
 				List<String> lines = removeComments(Files.readAllLines(file.toPath()));
-				springFactories.setProperty(file.getName(), StringUtils.collectionToCommaDelimitedString(lines));
+				String fileNameWithoutExtension = file.getName().substring(0,
+						file.getName().length() - ".imports".length());
+				springFactories.setProperty(fileNameWithoutExtension,
+						StringUtils.collectionToCommaDelimitedString(lines));
 			}
 			catch (IOException ex) {
 				throw new UncheckedIOException("Failed to read file " + file, ex);

spring-boot-project/spring-boot-autoconfigure/src/main/java/org/springframework/boot/autoconfigure/AutoConfiguration.java

@@ -24,6 +24,7 @@ import java.lang.annotation.Target;
 
 import org.springframework.boot.autoconfigure.condition.ConditionalOnClass;
 import org.springframework.boot.autoconfigure.condition.ConditionalOnMissingBean;
+import org.springframework.boot.context.annotation.ImportCandidates;
 import org.springframework.context.annotation.Conditional;
 import org.springframework.context.annotation.Configuration;
 import org.springframework.core.io.support.SpringFactoriesLoader;
@@ -34,9 +35,8 @@ import org.springframework.core.io.support.SpringFactoriesLoader;
  * {@link Configuration @Configuration} with the exception that
  * {@literal Configuration#proxyBeanMethods() proxyBeanMethods} is always {@code false}.
  * <p>
- * They are located using the {@link AutoConfigurationLoader} and the
- * {@link SpringFactoriesLoader} mechanism (keyed against
- * {@link EnableAutoConfiguration}).
+ * They are located using {@link ImportCandidates} and the {@link SpringFactoriesLoader}
+ * mechanism (keyed against {@link EnableAutoConfiguration}).
  * <p>
  * Generally auto-configuration classes are marked as {@link Conditional @Conditional}
  * (most often using {@link ConditionalOnClass @ConditionalOnClass} and

spring-boot-project/spring-boot-autoconfigure/src/main/java/org/springframework/boot/autoconfigure/AutoConfigurationExcludeFilter.java

@@ -21,6 +21,7 @@ import java.util.ArrayList;
 import java.util.List;
 
 import org.springframework.beans.factory.BeanClassLoaderAware;
+import org.springframework.boot.context.annotation.ImportCandidates;
 import org.springframework.context.annotation.Configuration;
 import org.springframework.core.io.support.SpringFactoriesLoader;
 import org.springframework.core.type.classreading.MetadataReader;
@@ -63,11 +64,9 @@ public class AutoConfigurationExcludeFilter implements TypeFilter, BeanClassLoad
 
 	protected List<String> getAutoConfigurations() {
 		if (this.autoConfigurations == null) {
-			List<String> autoConfigurations = new ArrayList<>();
-			autoConfigurations.addAll(
+			List<String> autoConfigurations = new ArrayList<>(
 					SpringFactoriesLoader.loadFactoryNames(EnableAutoConfiguration.class, this.beanClassLoader));
-			autoConfigurations
-					.addAll(new AutoConfigurationLoader().loadNames(AutoConfiguration.class, this.beanClassLoader));
+			ImportCandidates.load(AutoConfiguration.class, this.beanClassLoader).forEach(autoConfigurations::add);
 			this.autoConfigurations = autoConfigurations;
 		}
 		return this.autoConfigurations;

spring-boot-project/spring-boot-autoconfigure/src/main/java/org/springframework/boot/autoconfigure/AutoConfigurationImportSelector.java

@@ -40,6 +40,7 @@ import org.springframework.beans.factory.BeanFactory;
 import org.springframework.beans.factory.BeanFactoryAware;
 import org.springframework.beans.factory.NoSuchBeanDefinitionException;
 import org.springframework.beans.factory.config.ConfigurableListableBeanFactory;
+import org.springframework.boot.context.annotation.ImportCandidates;
 import org.springframework.boot.context.properties.bind.Binder;
 import org.springframework.context.EnvironmentAware;
 import org.springframework.context.ResourceLoaderAware;
@@ -168,7 +169,7 @@ public class AutoConfigurationImportSelector implements DeferredImportSelector,
 
 	/**
 	 * Return the auto-configuration class names that should be considered. By default
-	 * this method will load candidates using {@link AutoConfigurationLoader} with
+	 * this method will load candidates using {@link ImportCandidates} with
 	 * {@link #getSpringFactoriesLoaderFactoryClass()}. For backward compatible reasons it
 	 * will also consider {@link SpringFactoriesLoader} with
 	 * {@link #getSpringFactoriesLoaderFactoryClass()}.
@@ -178,12 +179,11 @@ public class AutoConfigurationImportSelector implements DeferredImportSelector,
 	 * @return a list of candidate configurations
 	 */
 	protected List<String> getCandidateConfigurations(AnnotationMetadata metadata, AnnotationAttributes attributes) {
-		List<String> configurations = new ArrayList<>();
-		configurations.addAll(
+		List<String> configurations = new ArrayList<>(
 				SpringFactoriesLoader.loadFactoryNames(getSpringFactoriesLoaderFactoryClass(), getBeanClassLoader()));
-		configurations.addAll(new AutoConfigurationLoader().loadNames(AutoConfiguration.class, getBeanClassLoader()));
+		ImportCandidates.load(AutoConfiguration.class, getBeanClassLoader()).forEach(configurations::add);
 		Assert.notEmpty(configurations,
-				"No auto configuration classes found in META-INF/spring.factories nor in META-INF/spring-boot/org.springframework.boot.autoconfigure.AutoConfiguration. If you "
+				"No auto configuration classes found in META-INF/spring.factories nor in META-INF/spring/org.springframework.boot.autoconfigure.AutoConfiguration.imports. If you "
 						+ "are using a custom packaging, make sure that file is correct.");
 		return configurations;
 	}

spring-boot-project/spring-boot-autoconfigure/src/main/java/org/springframework/boot/autoconfigure/EnableAutoConfiguration.java

@@ -26,6 +26,7 @@ import java.lang.annotation.Target;
 import org.springframework.boot.autoconfigure.condition.ConditionalOnBean;
 import org.springframework.boot.autoconfigure.condition.ConditionalOnClass;
 import org.springframework.boot.autoconfigure.condition.ConditionalOnMissingBean;
+import org.springframework.boot.context.annotation.ImportCandidates;
 import org.springframework.boot.web.embedded.tomcat.TomcatServletWebServerFactory;
 import org.springframework.boot.web.servlet.server.ServletWebServerFactory;
 import org.springframework.context.annotation.Conditional;
@@ -60,7 +61,7 @@ import org.springframework.core.io.support.SpringFactoriesLoader;
  * and classes can be searched.
  * <p>
  * Auto-configuration classes are regular Spring {@link Configuration @Configuration}
- * beans. They are located using the {@link AutoConfigurationLoader} and the
+ * beans. They are located using {@link ImportCandidates} and the
  * {@link SpringFactoriesLoader} mechanism (keyed against this class). Generally
  * auto-configuration beans are {@link Conditional @Conditional} beans (most often using
  * {@link ConditionalOnClass @ConditionalOnClass} and

spring-boot-project/spring-boot-autoconfigure/src/main/java/org/springframework/boot/autoconfigure/ImportAutoConfiguration.java

@@ -59,8 +59,8 @@ public @interface ImportAutoConfiguration {
 
 	/**
 	 * The auto-configuration classes that should be imported. When empty, the classes are
-	 * specified using a file in {@code META-INF/spring-boot} where the file name is the
-	 * fully-qualified name of the annotated class.
+	 * specified using a file in {@code META-INF/spring} where the file name is the
+	 * fully-qualified name of the annotated class, suffixed with '.imports'.
 	 * @return the classes to import
 	 */
 	@AliasFor("value")

spring-boot-project/spring-boot-autoconfigure/src/main/java/org/springframework/boot/autoconfigure/ImportAutoConfigurationImportSelector.java

@@ -1,5 +1,5 @@
 /*
- * Copyright 2012-2021 the original author or authors.
+ * Copyright 2012-2022 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.
@@ -28,6 +28,7 @@ import java.util.Map;
 import java.util.Set;
 
 import org.springframework.boot.context.annotation.DeterminableImports;
+import org.springframework.boot.context.annotation.ImportCandidates;
 import org.springframework.core.annotation.AnnotatedElementUtils;
 import org.springframework.core.annotation.AnnotationAttributes;
 import org.springframework.core.annotation.AnnotationUtils;
@@ -95,9 +96,9 @@ class ImportAutoConfigurationImportSelector extends AutoConfigurationImportSelec
 	}
 
 	protected Collection<String> loadFactoryNames(Class<?> source) {
-		List<String> factoryNames = new ArrayList<>();
-		factoryNames.addAll(SpringFactoriesLoader.loadFactoryNames(source, getBeanClassLoader()));
-		factoryNames.addAll(new AutoConfigurationLoader().loadNames(source, getBeanClassLoader()));
+		List<String> factoryNames = new ArrayList<>(
+				SpringFactoriesLoader.loadFactoryNames(source, getBeanClassLoader()));
+		ImportCandidates.load(source, getBeanClassLoader()).forEach(factoryNames::add);
 		return factoryNames;
 	}
 

spring-boot-project/spring-boot-autoconfigure/src/test/java/org/springframework/boot/autoconfigure/AutoConfigurationImportSelectorTests.java

@@ -32,6 +32,7 @@ import org.springframework.beans.factory.support.DefaultListableBeanFactory;
 import org.springframework.boot.autoconfigure.freemarker.FreeMarkerAutoConfiguration;
 import org.springframework.boot.autoconfigure.mustache.MustacheAutoConfiguration;
 import org.springframework.boot.autoconfigure.thymeleaf.ThymeleafAutoConfiguration;
+import org.springframework.boot.context.annotation.ImportCandidates;
 import org.springframework.context.annotation.Configuration;
 import org.springframework.core.io.DefaultResourceLoader;
 import org.springframework.core.type.AnnotationMetadata;
@@ -212,7 +213,10 @@ class AutoConfigurationImportSelectorTests {
 	}
 
 	private List<String> getAutoConfigurationClassNames() {
-		return new AutoConfigurationLoader().loadNames(AutoConfiguration.class, getClass().getClassLoader());
+		List<String> autoConfigurationClassNames = new ArrayList<>();
+		ImportCandidates.load(AutoConfiguration.class, getClass().getClassLoader())
+				.forEach(autoConfigurationClassNames::add);
+		return autoConfigurationClassNames;
 	}
 
 	private class TestAutoConfigurationImportSelector extends AutoConfigurationImportSelector {

spring-boot-project/spring-boot-docs/src/docs/asciidoc/features/developing-auto-configuration.adoc

@@ -18,14 +18,14 @@ Additional `@Conditional` annotations are used to constrain when the auto-config
 Usually, auto-configuration classes use `@ConditionalOnClass` and `@ConditionalOnMissingBean` annotations.
 This ensures that auto-configuration applies only when relevant classes are found and when you have not declared your own `@Configuration`.
 
-You can browse the source code of {spring-boot-autoconfigure-module-code}[`spring-boot-autoconfigure`] to see the `@Configuration` classes that Spring provides (see the {spring-boot-code}/spring-boot-project/spring-boot-autoconfigure/src/main/resources/META-INF/spring-boot/org.springframework.boot.autoconfigure.AutoConfiguration[`META-INF/spring-boot/org.springframework.boot.autoconfigure.AutoConfiguration`] file).
+You can browse the source code of {spring-boot-autoconfigure-module-code}[`spring-boot-autoconfigure`] to see the `@Configuration` classes that Spring provides (see the {spring-boot-code}/spring-boot-project/spring-boot-autoconfigure/src/main/resources/META-INF/spring/org.springframework.boot.autoconfigure.AutoConfiguration.imports[`META-INF/spring/org.springframework.boot.autoconfigure.AutoConfiguration.imports`] file).
 
 
 
 [[features.developing-auto-configuration.locating-auto-configuration-candidates]]
 === Locating Auto-configuration Candidates
 
-Spring Boot checks for the presence of a `META-INF/spring-boot/org.springframework.boot.autoconfigure.AutoConfiguration` file within your published jar.
+Spring Boot checks for the presence of a `META-INF/spring/org.springframework.boot.autoconfigure.AutoConfiguration.imports` file within your published jar.
 The file should list your configuration classes, as shown in the following example:
 
 [indent=0]

spring-boot-project/spring-boot-docs/src/docs/asciidoc/features/testing.adoc

@@ -769,9 +769,9 @@ include::code:MyJdbcTests[]
 
 NOTE: Make sure to not use the regular `@Import` annotation to import auto-configurations as they are handled in a specific way by Spring Boot.
 
-Alternatively, additional auto-configurations can be added for any use of a slice annotation by registering them in a file stored in `META-INF/spring-boot` as shown in the following example:
+Alternatively, additional auto-configurations can be added for any use of a slice annotation by registering them in a file stored in `META-INF/spring` as shown in the following example:
 
-.META-INF/spring-boot/org.springframework.boot.test.autoconfigure.jdbc.JdbcTest
+.META-INF/spring/org.springframework.boot.test.autoconfigure.jdbc.JdbcTest.imports
 [indent=0]
 ----
 	com.example.IntegrationAutoConfiguration

spring-boot-project/spring-boot/src/main/java/org/springframework/boot/context/annotation/ImportCandidates.java

@@ -14,7 +14,7 @@
  * limitations under the License.
  */
 
-package org.springframework.boot.autoconfigure;
+package org.springframework.boot.context.annotation;
 
 import java.io.BufferedReader;
 import java.io.IOException;
@@ -22,57 +22,76 @@ import java.io.InputStreamReader;
 import java.net.URL;
 import java.nio.charset.StandardCharsets;
 import java.util.ArrayList;
+import java.util.Collections;
 import java.util.Enumeration;
+import java.util.Iterator;
 import java.util.List;
 
+import org.jetbrains.annotations.NotNull;
+
 import org.springframework.core.io.UrlResource;
-import org.springframework.core.io.support.SpringFactoriesLoader;
 import org.springframework.util.Assert;
 
 /**
- * Loads the names of annotated classes, usually @{@link AutoConfiguration}.
+ * Contains import candidates, usually auto-configurations.
  *
- * The names of the classes are stored in files named META-INF/spring-boot/{full qualified
- * name of the annotation}. Every line contains the full qualified class name of the
- * annotated class. Comments are supported using the # character.
+ * The {@link #load(Class, ClassLoader)} method can be used to discover the import
+ * candidates.
  *
  * @author Moritz Halbritter
- * @see AutoConfiguration
- * @see SpringFactoriesLoader
+ * @since 2.7.0
  */
-class AutoConfigurationLoader {
+public final class ImportCandidates implements Iterable<String> {
 
-	private static final String LOCATION = "META-INF/spring-boot/";
+	private static final String LOCATION = "META-INF/spring/%s.imports";
 
 	private static final String COMMENT_START = "#";
 
+	private final List<String> candidates;
+
+	private ImportCandidates(List<String> candidates) {
+		Assert.notNull(candidates, "'candidates' must not be null");
+		this.candidates = Collections.unmodifiableList(candidates);
+	}
+
+	@NotNull
+	@Override
+	public Iterator<String> iterator() {
+		return this.candidates.iterator();
+	}
+
 	/**
-	 * Loads the names of annotated classes.
+	 * Loads the names of import candidates from the classpath.
+	 *
+	 * The names of the import candidates are stored in files named
+	 * {@code META-INF/spring/full-qualified-annotation-name.import} on the classpath.
+	 * Every line contains the full qualified name of the candidate class. Comments are
+	 * supported using the # character.
 	 * @param annotation annotation to load
 	 * @param classLoader class loader to use for loading
 	 * @return list of names of annotated classes
 	 */
-	List<String> loadNames(Class<?> annotation, ClassLoader classLoader) {
+	public static ImportCandidates load(Class<?> annotation, ClassLoader classLoader) {
 		Assert.notNull(annotation, "'annotation' must not be null");
 		ClassLoader classLoaderToUse = decideClassloader(classLoader);
-		String location = LOCATION + annotation.getName();
+		String location = String.format(LOCATION, annotation.getName());
 		Enumeration<URL> urls = findUrlsInClasspath(classLoaderToUse, location);
 		List<String> autoConfigurations = new ArrayList<>();
 		while (urls.hasMoreElements()) {
 			URL url = urls.nextElement();
 			autoConfigurations.addAll(readAutoConfigurations(url));
 		}
-		return autoConfigurations;
+		return new ImportCandidates(autoConfigurations);
 	}
 
-	private ClassLoader decideClassloader(ClassLoader classLoader) {
+	private static ClassLoader decideClassloader(ClassLoader classLoader) {
 		if (classLoader == null) {
-			return AutoConfigurationLoader.class.getClassLoader();
+			return ImportCandidates.class.getClassLoader();
 		}
 		return classLoader;
 	}
 
-	private Enumeration<URL> findUrlsInClasspath(ClassLoader classLoader, String location) {
+	private static Enumeration<URL> findUrlsInClasspath(ClassLoader classLoader, String location) {
 		try {
 			return classLoader.getResources(location);
 		}
@@ -82,7 +101,7 @@ class AutoConfigurationLoader {
 		}
 	}
 
-	private List<String> readAutoConfigurations(URL url) {
+	private static List<String> readAutoConfigurations(URL url) {
 		try (BufferedReader reader = new BufferedReader(
 				new InputStreamReader(new UrlResource(url).getInputStream(), StandardCharsets.UTF_8))) {
 			List<String> autoConfigurations = new ArrayList<>();
@@ -102,7 +121,7 @@ class AutoConfigurationLoader {
 		}
 	}
 
-	private String stripComment(String line) {
+	private static String stripComment(String line) {
 		int commentStart = line.indexOf(COMMENT_START);
 		if (commentStart == -1) {
 			return line;

spring-boot-project/spring-boot/src/test/java/org/springframework/boot/context/annotation/ImportCandidatesTest.java

@@ -14,39 +14,28 @@
  * limitations under the License.
  */
 
-package org.springframework.boot.autoconfigure;
+package org.springframework.boot.context.annotation;
 
 import java.lang.annotation.ElementType;
 import java.lang.annotation.Retention;
 import java.lang.annotation.RetentionPolicy;
 import java.lang.annotation.Target;
-import java.util.List;
 
-import org.junit.jupiter.api.BeforeEach;
 import org.junit.jupiter.api.Test;
 
 import static org.assertj.core.api.Assertions.assertThat;
 
-class AutoConfigurationLoaderTests {
-
-	private AutoConfigurationLoader sut;
-
-	@BeforeEach
-	void setUp() {
-		this.sut = new AutoConfigurationLoader();
-	}
+class ImportCandidatesTest {
 
 	@Test
-	void loadNames() {
-		List<String> classNames = this.sut.loadNames(TestAutoConfiguration.class, null);
-
-		assertThat(classNames).containsExactly("class1", "class2", "class3");
+	void loadReadsFromClasspathFile() {
+		ImportCandidates candidates = ImportCandidates.load(TestAnnotation.class, null);
+		assertThat(candidates).containsExactly("class1", "class2", "class3");
 	}
 
-	@AutoConfiguration
 	@Target(ElementType.TYPE)
 	@Retention(RetentionPolicy.RUNTIME)
-	public @interface TestAutoConfiguration {
+	public @interface TestAnnotation {
 
 	}