Add support for deferred import selector group

This commit allows several DeferredImportSelector instances to be
grouped and managed in a centralized fashion. This typically allows
different instances to provide a consistent ordered set of imports to
apply.

Issue: SPR-16589

spring-context/src/main/java/org/springframework/context/annotation/ConfigurationClassParser.java

@@ -51,6 +51,7 @@ import org.springframework.beans.factory.support.BeanDefinitionReader;
 import org.springframework.beans.factory.support.BeanDefinitionRegistry;
 import org.springframework.beans.factory.support.BeanNameGenerator;
 import org.springframework.context.annotation.ConfigurationCondition.ConfigurationPhase;
+import org.springframework.context.annotation.DeferredImportSelector.Group;
 import org.springframework.core.NestedIOException;
 import org.springframework.core.OrderComparator;
 import org.springframework.core.Ordered;
@@ -100,6 +101,7 @@ import org.springframework.util.StringUtils;
  * @author Juergen Hoeller
  * @author Phillip Webb
  * @author Sam Brannen
+ * @author Stephane Nicoll
  * @since 3.0
  * @see ConfigurationClassBeanDefinitionReader
  */
@@ -543,21 +545,46 @@ class ConfigurationClassParser {
 		}
 
 		deferredImports.sort(DEFERRED_IMPORT_COMPARATOR);
+		Map<Object, DeferredImportSelectorGrouping> groupings = new LinkedHashMap<>();
+		Map<AnnotationMetadata, ConfigurationClass> configurationClasses = new HashMap<>();
 		for (DeferredImportSelectorHolder deferredImport : deferredImports) {
-			ConfigurationClass configClass = deferredImport.getConfigurationClass();
-			try {
-				String[] imports = deferredImport.getImportSelector().selectImports(configClass.getMetadata());
-				processImports(configClass, asSourceClass(configClass), asSourceClasses(imports), false);
-			}
-			catch (BeanDefinitionStoreException ex) {
-				throw ex;
-			}
-			catch (Throwable ex) {
-				throw new BeanDefinitionStoreException(
-						"Failed to process import candidates for configuration class [" +
-						configClass.getMetadata().getClassName() + "]", ex);
-			}
+			Class<? extends Group> group = deferredImport.getImportSelector().getImportGroup();
+			DeferredImportSelectorGrouping grouping = groupings.computeIfAbsent(
+					(group == null ? deferredImport : group),
+					(key) -> new DeferredImportSelectorGrouping(createGroup(group)));
+			grouping.add(deferredImport);
+			configurationClasses.put(deferredImport.getConfigurationClass().getMetadata(),
+					deferredImport.getConfigurationClass());
 		}
+		for (DeferredImportSelectorGrouping grouping : groupings.values()) {
+			grouping.getImports().forEach((entry) -> {
+				ConfigurationClass configurationClass = configurationClasses.get(
+						entry.getMetadata());
+				try {
+					processImports(configurationClass, asSourceClass(configurationClass),
+							asSourceClasses(entry.getImportClassName()), false);
+				}
+				catch (BeanDefinitionStoreException ex) {
+					throw ex;
+				}
+				catch (Throwable ex) {
+					throw new BeanDefinitionStoreException(
+							"Failed to process import candidates for configuration class [" +
+									configurationClass.getMetadata().getClassName() + "]", ex);
+				}
+			});
+		}
+	}
+
+	private Group createGroup(@Nullable Class<? extends Group> type) {
+		Class<? extends Group> effectiveType = (type != null ? type
+				: DefaultDeferredImportSelectorGroup.class);
+		Group group = BeanUtils.instantiateClass(effectiveType);
+		ParserStrategyUtils.invokeAwareMethods(group,
+				ConfigurationClassParser.this.environment,
+				ConfigurationClassParser.this.resourceLoader,
+				ConfigurationClassParser.this.registry);
+		return group;
 	}
 
 	private void processImports(ConfigurationClass configClass, SourceClass currentSourceClass,
@@ -677,7 +704,7 @@ class ConfigurationClassParser {
 	/**
 	 * Factory method to obtain {@link SourceClass}s from class names.
 	 */
-	private Collection<SourceClass> asSourceClasses(String[] classNames) throws IOException {
+	private Collection<SourceClass> asSourceClasses(String... classNames) throws IOException {
 		List<SourceClass> annotatedClasses = new ArrayList<>(classNames.length);
 		for (String className : classNames) {
 			annotatedClasses.add(asSourceClass(className));
@@ -777,6 +804,52 @@ class ConfigurationClassParser {
 	}
 
 
+	private static class DeferredImportSelectorGrouping {
+
+		private final DeferredImportSelector.Group group;
+
+		private final List<DeferredImportSelectorHolder> deferredImports = new ArrayList<>();
+
+		DeferredImportSelectorGrouping(Group group) {
+			this.group = group;
+		}
+
+		public void add(DeferredImportSelectorHolder deferredImport) {
+			this.deferredImports.add(deferredImport);
+		}
+
+		/**
+		 * Return the imports defined by the group.
+		 * @return each import with its associated configuration class
+		 */
+		public Iterable<Group.Entry> getImports() {
+			for (DeferredImportSelectorHolder deferredImport : this.deferredImports) {
+				this.group.process(deferredImport.getConfigurationClass().getMetadata(),
+						deferredImport.getImportSelector());
+			}
+			return this.group.selectImports();
+		}
+	}
+
+
+	private static class DefaultDeferredImportSelectorGroup implements Group {
+
+		private final List<Entry> imports = new ArrayList<>();
+
+		@Override
+		public void process(AnnotationMetadata metadata, DeferredImportSelector selector) {
+			for (String importClassName : selector.selectImports(metadata)) {
+				this.imports.add(new Entry(metadata, importClassName));
+			}
+		}
+
+		@Override
+		public Iterable<Entry> selectImports() {
+			return this.imports;
+		}
+	}
+
+
 	/**
 	 * Simple wrapper that allows annotated source classes to be dealt with
 	 * in a uniform manner, regardless of how they are loaded.

spring-context/src/main/java/org/springframework/context/annotation/DeferredImportSelector.java

@@ -1,5 +1,5 @@
 /*
- * Copyright 2002-2013 the original author or authors.
+ * Copyright 2002-2018 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 +16,11 @@
 
 package org.springframework.context.annotation;
 
+import java.util.Objects;
+
+import org.springframework.core.type.AnnotationMetadata;
+import org.springframework.lang.Nullable;
+
 /**
  * A variation of {@link ImportSelector} that runs after all {@code @Configuration} beans
  * have been processed. This type of selector can be particularly useful when the selected
@@ -25,9 +30,90 @@ package org.springframework.context.annotation;
  * interface or use the {@link org.springframework.core.annotation.Order} annotation to
  * indicate a precedence against other {@link DeferredImportSelector}s.
  *
+ * <p>Implementations may also provide an {@link #getImportGroup() import group} which
+ * can provide additional sorting and filtering logic across different selectors.
+ *
  * @author Phillip Webb
+ * @author Stephane Nicoll
  * @since 4.0
  */
 public interface DeferredImportSelector extends ImportSelector {
 
+	/**
+	 * Return a specific import group or {@code null} if no grouping is required.
+	 * @return the import group class or {@code null}
+	 */
+	@Nullable
+	default Class<? extends Group> getImportGroup() {
+		return null;
+	}
+
+
+	/**
+	 * Interface used to group results from different import selectors.
+	 */
+	interface Group {
+
+		/**
+		 * Process the {@link AnnotationMetadata} of the importing @{@link Configuration}
+		 * class using the specified {@link DeferredImportSelector}.
+		 */
+		void process(AnnotationMetadata metadata, DeferredImportSelector selector);
+
+		/**
+		 * Return the {@link Entry entries} of which class(es) should be imported for this
+		 * group.
+		 */
+		Iterable<Entry> selectImports();
+
+		/**
+		 * An entry that holds the {@link AnnotationMetadata} of the importing
+		 * {@link Configuration} class and the class name to import.
+		 */
+		class Entry {
+
+			private final AnnotationMetadata metadata;
+
+			private final String importClassName;
+
+			public Entry(AnnotationMetadata metadata, String importClassName) {
+				this.metadata = metadata;
+				this.importClassName = importClassName;
+			}
+
+			/**
+			 * Return the {@link AnnotationMetadata} of the importing
+			 * {@link Configuration} class.
+			 */
+			public AnnotationMetadata getMetadata() {
+				return this.metadata;
+			}
+
+			/**
+			 * Return the fully qualified name of the class to import.
+			 */
+			public String getImportClassName() {
+				return this.importClassName;
+			}
+
+			@Override
+			public boolean equals(Object o) {
+				if (this == o) {
+					return true;
+				}
+				if (o == null || getClass() != o.getClass()) {
+					return false;
+				}
+				Entry entry = (Entry) o;
+				return Objects.equals(this.metadata, entry.metadata) &&
+						Objects.equals(this.importClassName, entry.importClassName);
+			}
+
+			@Override
+			public int hashCode() {
+				return Objects.hash(this.metadata, this.importClassName);
+			}
+		}
+	}
+
 }

spring-context/src/test/java/org/springframework/context/annotation/DeferredImportSelectorTests.java

@@ -0,0 +1,61 @@
+/*
+ * Copyright 2002-2018 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
+ *
+ *      http://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.context.annotation;
+
+import org.junit.Test;
+
+import org.springframework.context.annotation.DeferredImportSelector.Group;
+import org.springframework.core.type.AnnotationMetadata;
+
+import static org.junit.Assert.*;
+import static org.mockito.Mockito.*;
+
+/**
+ * Tests for {@link DeferredImportSelector}.
+ *
+ * @author Stephane Nicoll
+ */
+public class DeferredImportSelectorTests {
+
+	@Test
+	public void entryEqualsSameInstance() {
+		AnnotationMetadata metadata = mock(AnnotationMetadata.class);
+		Group.Entry entry = new Group.Entry(metadata, "com.example.Test");
+		assertEquals(entry, entry);
+	}
+
+	@Test
+	public void entryEqualsSameMetadataAndClassName() {
+		AnnotationMetadata metadata = mock(AnnotationMetadata.class);
+		assertEquals(new Group.Entry(metadata, "com.example.Test"),
+				new Group.Entry(metadata, "com.example.Test"));
+	}
+
+	@Test
+	public void entryEqualDifferentMetadataAndSameClassName() {
+		assertNotEquals(
+				new Group.Entry(mock(AnnotationMetadata.class), "com.example.Test"),
+				new Group.Entry(mock(AnnotationMetadata.class), "com.example.Test"));
+	}
+
+	@Test
+	public void entryEqualSameMetadataAnDifferentClassName() {
+		AnnotationMetadata metadata = mock(AnnotationMetadata.class);
+		assertNotEquals(new Group.Entry(metadata, "com.example.Test"),
+				new Group.Entry(metadata, "com.example.AnotherTest"));
+	}
+}

spring-context/src/test/java/org/springframework/context/annotation/ImportSelectorTests.java

@@ -20,13 +20,19 @@ import java.lang.annotation.ElementType;
 import java.lang.annotation.Retention;
 import java.lang.annotation.RetentionPolicy;
 import java.lang.annotation.Target;
+import java.util.Arrays;
+import java.util.Collections;
 import java.util.HashMap;
+import java.util.Iterator;
+import java.util.LinkedList;
 import java.util.Map;
+import java.util.concurrent.atomic.AtomicInteger;
 
 import org.hamcrest.Matcher;
-import org.junit.BeforeClass;
+import org.junit.Before;
 import org.junit.Test;
 import org.mockito.InOrder;
+
 import org.springframework.beans.BeansException;
 import org.springframework.beans.factory.BeanClassLoaderAware;
 import org.springframework.beans.factory.BeanFactory;
@@ -39,15 +45,20 @@ import org.springframework.core.annotation.Order;
 import org.springframework.core.env.Environment;
 import org.springframework.core.io.ResourceLoader;
 import org.springframework.core.type.AnnotationMetadata;
+import org.springframework.lang.Nullable;
+import org.springframework.util.LinkedMultiValueMap;
+import org.springframework.util.MultiValueMap;
 
 import static org.hamcrest.CoreMatchers.*;
 import static org.junit.Assert.*;
+import static org.mockito.Mockito.any;
 import static org.mockito.Mockito.*;
 
 /**
  * Tests for {@link ImportSelector} and {@link DeferredImportSelector}.
  *
  * @author Phillip Webb
+ * @author Stephane Nicoll
  */
 @SuppressWarnings("resource")
 public class ImportSelectorTests {
@@ -55,9 +66,11 @@ public class ImportSelectorTests {
 	static Map<Class<?>, String> importFrom = new HashMap<>();
 
 
-	@BeforeClass
-	public static void clearImportFrom() {
+	@Before
+	public void cleanup() {
 		ImportSelectorTests.importFrom.clear();
+		SampleImportSelector.cleanup();
+		TestImportGroup.cleanup();
 	}
 
 
@@ -94,6 +107,48 @@ public class ImportSelectorTests {
 		assertThat(importFrom.get(DeferredImportSelector2.class), isFromIndirect);
 	}
 
+	@Test
+	public void importSelectorsWithGroup() {
+		DefaultListableBeanFactory beanFactory = spy(new DefaultListableBeanFactory());
+		AnnotationConfigApplicationContext context = new AnnotationConfigApplicationContext(beanFactory);
+		context.register(GroupedConfig.class);
+		context.refresh();
+		InOrder ordered = inOrder(beanFactory);
+		ordered.verify(beanFactory).registerBeanDefinition(eq("a"), any());
+		ordered.verify(beanFactory).registerBeanDefinition(eq("b"), any());
+		ordered.verify(beanFactory).registerBeanDefinition(eq("c"), any());
+		ordered.verify(beanFactory).registerBeanDefinition(eq("d"), any());
+		assertThat(TestImportGroup.instancesCount.get(), equalTo(1));
+		assertThat(TestImportGroup.imports.size(), equalTo(1));
+		assertThat(TestImportGroup.imports.values().iterator().next().size(), equalTo(2));
+	}
+
+	@Test
+	public void importSelectorsSeparateWithGroup() {
+		DefaultListableBeanFactory beanFactory = spy(new DefaultListableBeanFactory());
+		AnnotationConfigApplicationContext context = new AnnotationConfigApplicationContext(beanFactory);
+		context.register(GroupedConfig1.class);
+		context.register(GroupedConfig2.class);
+		context.refresh();
+		InOrder ordered = inOrder(beanFactory);
+		ordered.verify(beanFactory).registerBeanDefinition(eq("c"), any());
+		ordered.verify(beanFactory).registerBeanDefinition(eq("d"), any());
+		assertThat(TestImportGroup.instancesCount.get(), equalTo(1));
+		assertThat(TestImportGroup.imports.size(), equalTo(2));
+		Iterator<AnnotationMetadata> iterator = TestImportGroup.imports.keySet().iterator();
+		assertThat(iterator.next().getClassName(), equalTo(GroupedConfig2.class.getName()));
+		assertThat(iterator.next().getClassName(), equalTo(GroupedConfig1.class.getName()));
+	}
+
+	@Test
+	public void invokeAwareMethodsInImportGroup() {
+		AnnotationConfigApplicationContext context = new AnnotationConfigApplicationContext(GroupedConfig1.class);
+		assertThat(TestImportGroup.beanFactory, is(context.getBeanFactory()));
+		assertThat(TestImportGroup.classLoader, is(context.getBeanFactory().getBeanClassLoader()));
+		assertThat(TestImportGroup.resourceLoader, is(notNullValue()));
+		assertThat(TestImportGroup.environment, is(context.getEnvironment()));
+	}
+
 
 	@Configuration
 	@Import(SampleImportSelector.class)
@@ -109,6 +164,13 @@ public class ImportSelectorTests {
 		static BeanFactory beanFactory;
 		static Environment environment;
 
+		static void cleanup() {
+			SampleImportSelector.classLoader = null;
+			SampleImportSelector.beanFactory = null;
+			SampleImportSelector.resourceLoader = null;
+			SampleImportSelector.environment = null;
+		}
+
 		@Override
 		public void setBeanClassLoader(ClassLoader classLoader) {
 			SampleImportSelector.classLoader = classLoader;
@@ -255,4 +317,107 @@ public class ImportSelectorTests {
 	public static class IndirectImport {
 	}
 
+
+	@GroupedSample
+	@Configuration
+	static class GroupedConfig {
+	}
+
+
+	@Target(ElementType.TYPE)
+	@Retention(RetentionPolicy.RUNTIME)
+	@Import({GroupedDeferredImportSelector1.class, GroupedDeferredImportSelector2.class, ImportSelector1.class, ImportSelector2.class})
+	public @interface GroupedSample {
+	}
+
+	@Configuration
+	@Import(GroupedDeferredImportSelector1.class)
+	static class GroupedConfig1 {
+	}
+
+	@Configuration
+	@Import(GroupedDeferredImportSelector2.class)
+	static class GroupedConfig2 {
+	}
+
+
+	public static class GroupedDeferredImportSelector1 extends DeferredImportSelector1 {
+
+		@Nullable
+		@Override
+		public Class<? extends Group> getImportGroup() {
+			return TestImportGroup.class;
+		}
+	}
+
+	public static class GroupedDeferredImportSelector2 extends DeferredImportSelector2 {
+
+		@Nullable
+		@Override
+		public Class<? extends Group> getImportGroup() {
+			return TestImportGroup.class;
+		}
+	}
+
+
+	public static class TestImportGroup implements DeferredImportSelector.Group,
+			BeanClassLoaderAware, ResourceLoaderAware, BeanFactoryAware, EnvironmentAware {
+
+		static ClassLoader classLoader;
+		static ResourceLoader resourceLoader;
+		static BeanFactory beanFactory;
+		static Environment environment;
+
+		static AtomicInteger instancesCount = new AtomicInteger();
+		static MultiValueMap<AnnotationMetadata, String> imports = new LinkedMultiValueMap<>();
+
+		public TestImportGroup() {
+			TestImportGroup.instancesCount.incrementAndGet();
+		}
+
+		static void cleanup() {
+			TestImportGroup.classLoader = null;
+			TestImportGroup.beanFactory = null;
+			TestImportGroup.resourceLoader = null;
+			TestImportGroup.environment = null;
+			TestImportGroup.instancesCount = new AtomicInteger();
+			TestImportGroup.imports.clear();
+		}
+
+		@Override
+		public void process(AnnotationMetadata metadata, DeferredImportSelector selector) {
+			TestImportGroup.imports.addAll(metadata,
+					Arrays.asList(selector.selectImports(metadata)));
+		}
+
+		@Override
+		public Iterable<Entry> selectImports() {
+			LinkedList<Entry> content = new LinkedList<>();
+			TestImportGroup.imports.forEach((metadata, values) ->
+				    values.forEach(value ->  content.add(new Entry(metadata, value))));
+			Collections.reverse(content);
+			return content;
+		}
+
+		@Override
+		public void setBeanClassLoader(ClassLoader classLoader) {
+			TestImportGroup.classLoader = classLoader;
+		}
+
+		@Override
+		public void setBeanFactory(BeanFactory beanFactory) throws BeansException {
+			TestImportGroup.beanFactory = beanFactory;
+		}
+
+		@Override
+		public void setResourceLoader(ResourceLoader resourceLoader) {
+			TestImportGroup.resourceLoader = resourceLoader;
+		}
+
+		@Override
+		public void setEnvironment(Environment environment) {
+			TestImportGroup.environment = environment;
+		}
+	}
+
 }