Merge branch '3.1.x'

Closes gh-36661

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

@@ -1,5 +1,5 @@
 /*
- * Copyright 2012-2022 the original author or authors.
+ * Copyright 2012-2023 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.
@@ -61,7 +61,9 @@ 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} where the file name is the
-	 * fully-qualified name of the annotated class, suffixed with '.imports'.
+	 * fully-qualified name of the annotated class, suffixed with {@code .imports}. An
+	 * entry in the file may be prefixed with {@code optional:} to indicate that the
+	 * imported class should be ignored if it is not on the classpath.
 	 * @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 2012-2022 the original author or authors.
+ * Copyright 2012-2023 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.
@@ -25,6 +25,7 @@ import java.util.HashSet;
 import java.util.LinkedHashSet;
 import java.util.List;
 import java.util.Map;
+import java.util.Objects;
 import java.util.Set;
 
 import org.springframework.boot.context.annotation.DeterminableImports;
@@ -32,6 +33,7 @@ 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;
+import org.springframework.core.io.ClassPathResource;
 import org.springframework.core.type.AnnotationMetadata;
 import org.springframework.util.ClassUtils;
 import org.springframework.util.LinkedMultiValueMap;
@@ -49,6 +51,8 @@ import org.springframework.util.ObjectUtils;
  */
 class ImportAutoConfigurationImportSelector extends AutoConfigurationImportSelector implements DeterminableImports {
 
+	private static final String OPTIONAL_PREFIX = "optional:";
+
 	private static final Set<String> ANNOTATION_NAMES;
 
 	static {
@@ -92,13 +96,27 @@ class ImportAutoConfigurationImportSelector extends AutoConfigurationImportSelec
 		if (classes.length > 0) {
 			return Arrays.asList(classes);
 		}
-		return loadFactoryNames(source);
+		Collection<String> factoryNames = loadFactoryNames(source);
+		return factoryNames.stream().map((name) -> {
+			if (name.startsWith(OPTIONAL_PREFIX)) {
+				name = name.substring(OPTIONAL_PREFIX.length());
+				if (!present(name)) {
+					return null;
+				}
+			}
+			return name;
+		}).filter(Objects::nonNull).toList();
 	}
 
 	protected Collection<String> loadFactoryNames(Class<?> source) {
 		return ImportCandidates.load(source, getBeanClassLoader()).getCandidates();
 	}
 
+	private boolean present(String className) {
+		String resourcePath = ClassUtils.convertClassNameToResourcePath(className) + ".class";
+		return new ClassPathResource(resourcePath).exists();
+	}
+
 	@Override
 	protected Set<String> getExclusions(AnnotationMetadata metadata, AnnotationAttributes attributes) {
 		Set<String> exclusions = new LinkedHashSet<>();

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

@@ -74,6 +74,25 @@ class ImportAutoConfigurationImportSelectorTests {
 		assertThat(imports).containsExactly(FreeMarkerAutoConfiguration.class.getName());
 	}
 
+	@Test
+	void importsAreSelectedFromImportsFile() throws Exception {
+		AnnotationMetadata annotationMetadata = getAnnotationMetadata(FromImportsFile.class);
+		String[] imports = this.importSelector.selectImports(annotationMetadata);
+		assertThat(imports).containsExactly(
+				"org.springframework.boot.autoconfigure.freemarker.FreeMarkerAutoConfiguration",
+				"org.springframework.boot.autoconfigure.missing.MissingAutoConfiguration");
+	}
+
+	@Test
+	void importsSelectedFromImportsFileIgnoreMissingOptionalClasses() throws Exception {
+		AnnotationMetadata annotationMetadata = getAnnotationMetadata(
+				FromImportsFileIgnoresMissingOptionalClasses.class);
+		String[] imports = this.importSelector.selectImports(annotationMetadata);
+		assertThat(imports).containsExactly(
+				"org.springframework.boot.autoconfigure.freemarker.FreeMarkerAutoConfiguration",
+				"org.springframework.boot.autoconfigure.thymeleaf.ThymeleafAutoConfiguration");
+	}
+
 	@Test
 	void propertyExclusionsAreApplied() throws IOException {
 		this.environment.setProperty("spring.autoconfigure.exclude", FreeMarkerAutoConfiguration.class.getName());
@@ -312,6 +331,18 @@ class ImportAutoConfigurationImportSelectorTests {
 
 	}
 
+	@Retention(RetentionPolicy.RUNTIME)
+	@ImportAutoConfiguration
+	@interface FromImportsFile {
+
+	}
+
+	@Retention(RetentionPolicy.RUNTIME)
+	@ImportAutoConfiguration
+	@interface FromImportsFileIgnoresMissingOptionalClasses {
+
+	}
+
 	static class TestImportAutoConfigurationImportSelector extends ImportAutoConfigurationImportSelector {
 
 		@Override

spring-boot-project/spring-boot-autoconfigure/src/test/resources/META-INF/spring/org.springframework.boot.autoconfigure.ImportAutoConfigurationImportSelectorTests$FromImportsFile.imports

@@ -0,0 +1,2 @@
+org.springframework.boot.autoconfigure.freemarker.FreeMarkerAutoConfiguration
+org.springframework.boot.autoconfigure.missing.MissingAutoConfiguration

spring-boot-project/spring-boot-autoconfigure/src/test/resources/META-INF/spring/org.springframework.boot.autoconfigure.ImportAutoConfigurationImportSelectorTests$FromImportsFileIgnoresMissingOptionalClasses.imports

@@ -0,0 +1,3 @@
+optional:org.springframework.boot.autoconfigure.freemarker.FreeMarkerAutoConfiguration
+optional:org.springframework.boot.autoconfigure.missing.MissingAutoConfiguration
+org.springframework.boot.autoconfigure.thymeleaf.ThymeleafAutoConfiguration