Add AutoConfigurationImportFilter support

Add `AutoConfigurationImportFilter` strategy interface which can be used
to filter auto-configuration candidates before they are loaded.

See gh-7573

Author: philwebb

spring-boot-autoconfigure/src/main/java/org/springframework/boot/autoconfigure/AutoConfigurationImportFilter.java

@@ -0,0 +1,58 @@
+/*
+ * Copyright 2012-2017 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.boot.autoconfigure;
+
+import org.springframework.beans.factory.BeanClassLoaderAware;
+import org.springframework.beans.factory.BeanFactoryAware;
+import org.springframework.context.EnvironmentAware;
+import org.springframework.context.ResourceLoaderAware;
+
+/**
+ * Filter that can be registered in {@code spring.factories} to limit the
+ * auto-configuration classes considered. This interface is designed to allow fast removal
+ * of auto-configuration classes before their bytecode is even read.
+ * <p>
+ * An {@link AutoConfigurationImportFilter} may implement any of the following
+ * {@link org.springframework.beans.factory.Aware Aware} interfaces, and their respective
+ * methods will be called prior to {@link #match}:
+ * <ul>
+ * <li>{@link EnvironmentAware}</li>
+ * <li>{@link BeanFactoryAware }</li>
+ * <li>{@link BeanClassLoaderAware }</li>
+ * <li>{@link ResourceLoaderAware}</li>
+ * </ul>
+ *
+ * @author Phillip Webb
+ * @since 1.5.0
+ */
+public interface AutoConfigurationImportFilter {
+
+	/**
+	 * Apply the filter to the given auto-configuration class candidates.
+	 * @param autoConfigurationClasses the auto-configuration classes being considered.
+	 * Implementations should not change the values in this array.
+	 * @param autoConfigurationMetadata access to the meta-data generated by the
+	 * auto-configure annotation processor
+	 * @return a boolean array indicating which of the auto-configuration classes should
+	 * be imported. The returned array must be the same size as the incoming
+	 * {@code autoConfigurationClasses} parameter. Entries containing {@code false} will
+	 * not be imported.
+	 */
+	boolean[] match(String[] autoConfigurationClasses,
+			AutoConfigurationMetadata autoConfigurationMetadata);
+
+}

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

@@ -24,6 +24,10 @@
 import java.util.List;
 import java.util.Map;
 import java.util.Set;
+import java.util.concurrent.TimeUnit;
+
+import org.apache.commons.logging.Log;
+import org.apache.commons.logging.LogFactory;
 
 import org.springframework.beans.BeansException;
 import org.springframework.beans.factory.Aware;
@@ -67,6 +71,9 @@ public class AutoConfigurationImportSelector
 
 	private static final String[] NO_IMPORTS = {};
 
+	private static final Log logger = LogFactory
+			.getLog(AutoConfigurationImportSelector.class);
+
 	private ConfigurableListableBeanFactory beanFactory;
 
 	private Environment environment;
@@ -91,6 +98,7 @@ public String[] selectImports(AnnotationMetadata annotationMetadata) {
 			Set<String> exclusions = getExclusions(annotationMetadata, attributes);
 			checkExcludedClasses(configurations, exclusions);
 			configurations.removeAll(exclusions);
+			configurations = filter(configurations, autoConfigurationMetadata);
 			fireAutoConfigurationImportListeners(configurations, exclusions);
 			return configurations.toArray(new String[configurations.size()]);
 		}
@@ -233,6 +241,45 @@ private List<String> sort(List<String> configurations,
 		return configurations;
 	}
 
+	private List<String> filter(List<String> configurations,
+			AutoConfigurationMetadata autoConfigurationMetadata) {
+		long startTime = System.nanoTime();
+		String[] candidates = configurations.toArray(new String[configurations.size()]);
+		boolean[] skip = new boolean[candidates.length];
+		boolean skipped = false;
+		for (AutoConfigurationImportFilter filter : getAutoConfigurationImportFilters()) {
+			invokeAwareMethods(filter);
+			boolean[] match = filter.match(candidates, autoConfigurationMetadata);
+			for (int i = 0; i < match.length; i++) {
+				if (!match[i]) {
+					skip[i] = true;
+					skipped = true;
+				}
+			}
+		}
+		if (!skipped) {
+			return configurations;
+		}
+		List<String> result = new ArrayList<String>(candidates.length);
+		for (int i = 0; i < candidates.length; i++) {
+			if (!skip[i]) {
+				result.add(candidates[i]);
+			}
+		}
+		if (logger.isTraceEnabled()) {
+			int numberFiltered = configurations.size() - result.size();
+			logger.trace("Filtered " + numberFiltered + " auto configuration class in "
+					+ TimeUnit.NANOSECONDS.toMillis(System.nanoTime() - startTime)
+					+ " ms");
+		}
+		return new ArrayList<String>(result);
+	}
+
+	protected List<AutoConfigurationImportFilter> getAutoConfigurationImportFilters() {
+		return SpringFactoriesLoader.loadFactories(AutoConfigurationImportFilter.class,
+				this.beanClassLoader);
+	}
+
 	private MetadataReaderFactory getMetadataReaderFactory() {
 		try {
 			return getBeanFactory().getBean(
@@ -271,20 +318,20 @@ protected List<AutoConfigurationImportListener> getAutoConfigurationImportListen
 				this.beanClassLoader);
 	}
 
-	private void invokeAwareMethods(AutoConfigurationImportListener listener) {
-		if (listener instanceof Aware) {
-			if (listener instanceof BeanClassLoaderAware) {
-				((BeanClassLoaderAware) listener)
+	private void invokeAwareMethods(Object instance) {
+		if (instance instanceof Aware) {
+			if (instance instanceof BeanClassLoaderAware) {
+				((BeanClassLoaderAware) instance)
 						.setBeanClassLoader(this.beanClassLoader);
 			}
-			if (listener instanceof BeanFactoryAware) {
-				((BeanFactoryAware) listener).setBeanFactory(this.beanFactory);
+			if (instance instanceof BeanFactoryAware) {
+				((BeanFactoryAware) instance).setBeanFactory(this.beanFactory);
 			}
-			if (listener instanceof EnvironmentAware) {
-				((EnvironmentAware) listener).setEnvironment(this.environment);
+			if (instance instanceof EnvironmentAware) {
+				((EnvironmentAware) instance).setEnvironment(this.environment);
 			}
-			if (listener instanceof ResourceLoaderAware) {
-				((ResourceLoaderAware) listener).setResourceLoader(this.resourceLoader);
+			if (instance instanceof ResourceLoaderAware) {
+				((ResourceLoaderAware) instance).setResourceLoader(this.resourceLoader);
 			}
 		}
 	}

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

@@ -16,15 +16,21 @@
 
 package org.springframework.boot.autoconfigure;
 
+import java.util.ArrayList;
 import java.util.Collections;
+import java.util.HashSet;
 import java.util.List;
+import java.util.Set;
 
 import org.junit.Before;
 import org.junit.Rule;
 import org.junit.Test;
 import org.junit.rules.ExpectedException;
 import org.mockito.MockitoAnnotations;
 
+import org.springframework.beans.BeansException;
+import org.springframework.beans.factory.BeanFactory;
+import org.springframework.beans.factory.BeanFactoryAware;
 import org.springframework.beans.factory.config.ConfigurableListableBeanFactory;
 import org.springframework.beans.factory.support.DefaultListableBeanFactory;
 import org.springframework.boot.autoconfigure.freemarker.FreeMarkerAutoConfiguration;
@@ -53,6 +59,8 @@ public class AutoConfigurationImportSelectorTests {
 
 	private final MockEnvironment environment = new MockEnvironment();
 
+	private List<AutoConfigurationImportFilter> filters = new ArrayList<AutoConfigurationImportFilter>();
+
 	@Rule
 	public ExpectedException expected = ExpectedException.none();
 
@@ -191,6 +199,26 @@ public void nameAndPropertyExclusionsWhenNotPresentOnClasspathShouldNotThrowExce
 						"org.springframework.boot.autoconfigure.DoesNotExist2");
 	}
 
+	@Test
+	public void filterShouldFilterImports() throws Exception {
+		String[] defaultImports = selectImports(BasicEnableAutoConfiguration.class);
+		this.filters.add(new TestAutoConfigurationImportFilter(defaultImports, 1));
+		this.filters.add(new TestAutoConfigurationImportFilter(defaultImports, 3, 4));
+		String[] filtered = selectImports(BasicEnableAutoConfiguration.class);
+		assertThat(filtered).hasSize(defaultImports.length - 3);
+		assertThat(filtered).doesNotContain(defaultImports[1], defaultImports[3],
+				defaultImports[4]);
+	}
+
+	@Test
+	public void filterShouldSupportAware() throws Exception {
+		TestAutoConfigurationImportFilter filter = new TestAutoConfigurationImportFilter(
+				new String[] {});
+		this.filters.add(filter);
+		selectImports(BasicEnableAutoConfiguration.class);
+		assertThat(filter.getBeanFactory()).isEqualTo(this.beanFactory);
+	}
+
 	private String[] selectImports(Class<?> source) {
 		return this.importSelector.selectImports(new StandardAnnotationMetadata(source));
 	}
@@ -200,11 +228,16 @@ private List<String> getAutoConfigurationClassNames() {
 				getClass().getClassLoader());
 	}
 
-	private static class TestAutoConfigurationImportSelector
+	private class TestAutoConfigurationImportSelector
 			extends AutoConfigurationImportSelector {
 
 		private AutoConfigurationImportEvent lastEvent;
 
+		@Override
+		protected List<AutoConfigurationImportFilter> getAutoConfigurationImportFilters() {
+			return AutoConfigurationImportSelectorTests.this.filters;
+		}
+
 		@Override
 		protected List<AutoConfigurationImportListener> getAutoConfigurationImportListeners() {
 			return Collections.<AutoConfigurationImportListener>singletonList(
@@ -225,6 +258,40 @@ public AutoConfigurationImportEvent getLastEvent() {
 
 	}
 
+	private static class TestAutoConfigurationImportFilter
+			implements AutoConfigurationImportFilter, BeanFactoryAware {
+
+		private final Set<String> nonMatching = new HashSet<String>();
+
+		private BeanFactory beanFactory;
+
+		TestAutoConfigurationImportFilter(String[] configurations, int... nonMatching) {
+			for (int i : nonMatching) {
+				this.nonMatching.add(configurations[i]);
+			}
+		}
+
+		@Override
+		public boolean[] match(String[] autoConfigurationClasses,
+				AutoConfigurationMetadata autoConfigurationMetadata) {
+			boolean[] result = new boolean[autoConfigurationClasses.length];
+			for (int i = 0; i < result.length; i++) {
+				result[i] = !this.nonMatching.contains(autoConfigurationClasses[i]);
+			}
+			return result;
+		}
+
+		@Override
+		public void setBeanFactory(BeanFactory beanFactory) throws BeansException {
+			this.beanFactory = beanFactory;
+		}
+
+		public BeanFactory getBeanFactory() {
+			return this.beanFactory;
+		}
+
+	}
+
 	@Configuration
 	private class TestConfiguration {