Support ordering of auto-configuration classes

Update EnableAutoConfigurationImportSelector to sort auto-configuration
classes based on @Order and @AutoConfigureAfter annotations.

spring-bootstrap/src/main/java/org/springframework/bootstrap/context/annotation/AutoConfigurationSorter.java

@@ -0,0 +1,172 @@
+/*
+ * Copyright 2012-2013 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.bootstrap.context.annotation;
+
+import java.io.IOException;
+import java.util.ArrayList;
+import java.util.Collection;
+import java.util.Collections;
+import java.util.LinkedHashSet;
+import java.util.List;
+import java.util.Map;
+import java.util.Set;
+
+import org.springframework.core.OrderComparator;
+import org.springframework.core.Ordered;
+import org.springframework.core.annotation.Order;
+import org.springframework.core.io.ResourceLoader;
+import org.springframework.core.type.AnnotationMetadata;
+import org.springframework.core.type.classreading.CachingMetadataReaderFactory;
+import org.springframework.core.type.classreading.MetadataReader;
+import org.springframework.util.Assert;
+
+/**
+ * Sort {@link EnableAutoConfiguration auto-configuration} classes into priority order by
+ * reading {@link Ordered} and {@link AutoConfigureAfter} annotations (without loading
+ * classes).
+ * 
+ * @author Phillip Webb
+ */
+class AutoConfigurationSorter {
+
+	private CachingMetadataReaderFactory metadataReaderFactory;
+
+	public AutoConfigurationSorter(ResourceLoader resourceLoader) {
+		Assert.notNull(resourceLoader, "ResourceLoader must not be null");
+		this.metadataReaderFactory = new CachingMetadataReaderFactory(resourceLoader);
+	}
+
+	public List<String> getInPriorityOrder(Collection<String> classNames)
+			throws IOException {
+		List<AutoConfigurationClass> autoConfigurationClasses = new ArrayList<AutoConfigurationClass>();
+		for (String className : classNames) {
+			autoConfigurationClasses.add(new AutoConfigurationClass(className));
+		}
+
+		// Sort initially by order
+		Collections.sort(autoConfigurationClasses, OrderComparator.INSTANCE);
+
+		// Then respect @AutoConfigureAfter
+		autoConfigurationClasses = sortByAfterAnnotation(autoConfigurationClasses);
+
+		List<String> orderedClassNames = new ArrayList<String>();
+		for (AutoConfigurationClass autoConfigurationClass : autoConfigurationClasses) {
+			orderedClassNames.add(autoConfigurationClass.toString());
+		}
+		return orderedClassNames;
+	}
+
+	private List<AutoConfigurationClass> sortByAfterAnnotation(
+			Collection<AutoConfigurationClass> autoConfigurationClasses)
+			throws IOException {
+		List<AutoConfigurationClass> tosort = new ArrayList<AutoConfigurationClass>(
+				autoConfigurationClasses);
+		Set<AutoConfigurationClass> sorted = new LinkedHashSet<AutoConfigurationClass>();
+		Set<AutoConfigurationClass> processing = new LinkedHashSet<AutoConfigurationClass>();
+		while (!tosort.isEmpty()) {
+			doSortByAfterAnnotation(tosort, sorted, processing, null);
+		}
+		return new ArrayList<AutoConfigurationClass>(sorted);
+	}
+
+	private void doSortByAfterAnnotation(List<AutoConfigurationClass> tosort,
+			Set<AutoConfigurationClass> sorted, Set<AutoConfigurationClass> processing,
+			AutoConfigurationClass current) throws IOException {
+
+		if (current == null) {
+			current = tosort.remove(0);
+		}
+
+		processing.add(current);
+
+		for (AutoConfigurationClass after : current.getAfter()) {
+			Assert.state(!processing.contains(after),
+					"Cycle @AutoConfigureAfter detected between " + current + " and "
+							+ after);
+			if (!sorted.contains(after) && tosort.contains(after)) {
+				doSortByAfterAnnotation(tosort, sorted, processing, after);
+			}
+		}
+
+		processing.remove(current);
+		sorted.add(current);
+	}
+
+	private class AutoConfigurationClass implements Ordered {
+
+		private final String className;
+
+		private final int order;
+
+		private List<AutoConfigurationClass> after;
+
+		private Map<String, Object> afterAnnotation;
+
+		public AutoConfigurationClass(String className) throws IOException {
+
+			this.className = className;
+
+			MetadataReader metadataReader = AutoConfigurationSorter.this.metadataReaderFactory
+					.getMetadataReader(className);
+			AnnotationMetadata metadata = metadataReader.getAnnotationMetadata();
+
+			// Read @Order annotation
+			Map<String, Object> orderedAnnotation = metadata
+					.getAnnotationAttributes(Order.class.getName());
+			this.order = (orderedAnnotation == null ? Ordered.LOWEST_PRECEDENCE
+					: (Integer) orderedAnnotation.get("value"));
+
+			// Read @AutoConfigureAfter annotation
+			this.afterAnnotation = metadata.getAnnotationAttributes(
+					AutoConfigureAfter.class.getName(), true);
+		}
+
+		@Override
+		public int getOrder() {
+			return this.order;
+		}
+
+		public List<AutoConfigurationClass> getAfter() throws IOException {
+			if (this.after == null) {
+				if (this.afterAnnotation == null) {
+					this.after = Collections.emptyList();
+				} else {
+					this.after = new ArrayList<AutoConfigurationClass>();
+					for (String afterClass : (String[]) this.afterAnnotation.get("value")) {
+						this.after.add(new AutoConfigurationClass(afterClass));
+					}
+				}
+			}
+			return this.after;
+		}
+
+		@Override
+		public String toString() {
+			return this.className;
+		}
+
+		@Override
+		public int hashCode() {
+			return this.className.hashCode();
+		}
+
+		@Override
+		public boolean equals(Object obj) {
+			return this.className.equals(((AutoConfigurationClass) obj).className);
+		}
+	}
+
+}

spring-bootstrap/src/main/java/org/springframework/bootstrap/context/annotation/AutoConfigureAfter.java

@@ -0,0 +1,33 @@
+/*
+ * Copyright 2012-2013 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.bootstrap.context.annotation;
+
+import java.lang.annotation.ElementType;
+import java.lang.annotation.Retention;
+import java.lang.annotation.RetentionPolicy;
+import java.lang.annotation.Target;
+
+/**
+ * Hint for that an {@link EnableAutoConfiguration auto-configuration} should be applied
+ * after the specified auto-configuration classes.
+ * 
+ * @author Phillip Webb
+ */
+@Retention(RetentionPolicy.RUNTIME)
+@Target({ ElementType.TYPE })
+public @interface AutoConfigureAfter {
+	Class<?>[] value();
+}

spring-bootstrap/src/main/java/org/springframework/bootstrap/context/annotation/EnableAutoConfiguration.java

@@ -55,6 +55,7 @@ import org.springframework.core.io.support.SpringFactoriesLoader;
  * @see ConditionalOnBean
  * @see ConditionalOnMissingBean
  * @see ConditionalOnClass
+ * @see AutoConfigureAfter
  */
 @Target(ElementType.TYPE)
 @Retention(RetentionPolicy.RUNTIME)

spring-bootstrap/src/main/java/org/springframework/bootstrap/context/annotation/EnableAutoConfigurationImportSelector.java

@@ -16,15 +16,18 @@
 
 package org.springframework.bootstrap.context.annotation;
 
+import java.io.IOException;
 import java.util.ArrayList;
 import java.util.Arrays;
 import java.util.List;
 
 import org.springframework.beans.factory.BeanClassLoaderAware;
+import org.springframework.context.ResourceLoaderAware;
 import org.springframework.context.annotation.DeferredImportSelector;
 import org.springframework.core.Ordered;
 import org.springframework.core.annotation.AnnotationAttributes;
 import org.springframework.core.annotation.Order;
+import org.springframework.core.io.ResourceLoader;
 import org.springframework.core.io.support.SpringFactoriesLoader;
 import org.springframework.core.type.AnnotationMetadata;
 
@@ -37,19 +40,38 @@ import org.springframework.core.type.AnnotationMetadata;
  */
 @Order(Ordered.LOWEST_PRECEDENCE)
 class EnableAutoConfigurationImportSelector implements DeferredImportSelector,
-		BeanClassLoaderAware {
+		BeanClassLoaderAware, ResourceLoaderAware {
 
 	private ClassLoader beanClassLoader;
 
+	private ResourceLoader resourceLoader;
+
 	@Override
 	public String[] selectImports(AnnotationMetadata metadata) {
-		AnnotationAttributes attributes = AnnotationAttributes.fromMap(metadata
+		try {
-				.getAnnotationAttributes(EnableAutoConfiguration.class.getName(), true));
+			AnnotationAttributes attributes = AnnotationAttributes.fromMap(metadata
-		List<String> factories = new ArrayList<String>(
+					.getAnnotationAttributes(EnableAutoConfiguration.class.getName(),
-				SpringFactoriesLoader.loadFactoryNames(EnableAutoConfiguration.class,
+							true));
-						this.beanClassLoader));
+
-		factories.removeAll(Arrays.asList(attributes.getStringArray("exclude")));
+			// Find all possible auto configuration classes
-		return factories.toArray(new String[factories.size()]);
+			List<String> factories = new ArrayList<String>(
+					SpringFactoriesLoader.loadFactoryNames(EnableAutoConfiguration.class,
+							this.beanClassLoader));
+
+			// Remove those specifically disabled
+			factories.removeAll(Arrays.asList(attributes.getStringArray("exclude")));
+
+			// Sort
+			factories = new AutoConfigurationSorter(this.resourceLoader)
+					.getInPriorityOrder(factories);
+
+			// Always add the ComponentScanDetector as the first in the list
+			factories.add(0, ComponentScanDetector.class.getName());
+
+			return factories.toArray(new String[factories.size()]);
+		} catch (IOException ex) {
+			throw new IllegalStateException(ex);
+		}
 	}
 
 	@Override
@@ -57,4 +79,9 @@ class EnableAutoConfigurationImportSelector implements DeferredImportSelector,
 		this.beanClassLoader = classLoader;
 	}
 
+	@Override
+	public void setResourceLoader(ResourceLoader resourceLoader) {
+		this.resourceLoader = resourceLoader;
+	}
+
 }

spring-bootstrap/src/test/java/org/springframework/bootstrap/context/annotation/AutoConfigurationSorterTest.java

@@ -0,0 +1,104 @@
+/*
+ * Copyright 2012-2013 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.bootstrap.context.annotation;
+
+import java.util.Arrays;
+import java.util.List;
+
+import org.junit.Before;
+import org.junit.Rule;
+import org.junit.Test;
+import org.junit.rules.ExpectedException;
+import org.springframework.core.Ordered;
+import org.springframework.core.annotation.Order;
+import org.springframework.core.io.DefaultResourceLoader;
+
+import static org.hamcrest.Matchers.equalTo;
+import static org.junit.Assert.assertThat;
+
+/**
+ * Tests for {@link AutoConfigurationSorter}.
+ * 
+ * @author Phillip Webb
+ */
+public class AutoConfigurationSorterTest {
+
+	private static final String LOWEST = OrderLowest.class.getName();
+	private static final String HIGHEST = OrderHighest.class.getName();
+	private static final String A = AutoConfigureA.class.getName();
+	private static final String B = AutoConfigureB.class.getName();
+	private static final String C = AutoConfigureC.class.getName();
+	private static final String D = AutoConfigureD.class.getName();
+
+	@Rule
+	public ExpectedException thrown = ExpectedException.none();
+
+	private AutoConfigurationSorter sorter;
+
+	@Before
+	public void setup() {
+		this.sorter = new AutoConfigurationSorter(new DefaultResourceLoader());
+	}
+
+	@Test
+	public void byOrderAnnotation() throws Exception {
+		List<String> actual = this.sorter.getInPriorityOrder(Arrays.asList(LOWEST,
+				HIGHEST));
+		assertThat(actual, equalTo(Arrays.asList(HIGHEST, LOWEST)));
+	}
+
+	@Test
+	public void byAutoConfigureAfter() throws Exception {
+		List<String> actual = this.sorter.getInPriorityOrder(Arrays.asList(A, B, C));
+		assertThat(actual, equalTo(Arrays.asList(C, B, A)));
+	}
+
+	@Test
+	public void byAutoConfigureAfterWithMissing() throws Exception {
+		List<String> actual = this.sorter.getInPriorityOrder(Arrays.asList(A, B));
+		assertThat(actual, equalTo(Arrays.asList(B, A)));
+	}
+
+	@Test
+	public void byAutoConfigureAfterWithCycle() throws Exception {
+		this.thrown.expect(IllegalStateException.class);
+		this.thrown.expectMessage("Cycle");
+		this.sorter.getInPriorityOrder(Arrays.asList(A, B, C, D));
+	}
+
+	@Order(Ordered.LOWEST_PRECEDENCE)
+	public static class OrderLowest {
+	}
+
+	@Order(Ordered.HIGHEST_PRECEDENCE)
+	public static class OrderHighest {
+	}
+
+	@AutoConfigureAfter(AutoConfigureB.class)
+	public static class AutoConfigureA {
+	}
+
+	@AutoConfigureAfter({ AutoConfigureC.class, AutoConfigureD.class })
+	public static class AutoConfigureB {
+	}
+
+	public static class AutoConfigureC {
+	}
+
+	@AutoConfigureAfter(AutoConfigureA.class)
+	public static class AutoConfigureD {
+	}
+}