Add AutoConfigurationImportFilter base classes

Add `FilteringSpringBootCondition` base class and refactor the existing
`OnClassCondition` to use it. Also update the `match` method so that
the `autoConfigurationClasses` array may include `null` elements.

See gh-13328

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

@@ -1,5 +1,5 @@
 /*
- * Copyright 2012-2017 the original author or authors.
+ * Copyright 2012-2018 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.
@@ -45,7 +45,8 @@ 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.
+	 * This array may contain {@code null} elements. 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

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

@@ -263,6 +263,7 @@ private List<String> filter(List<String> configurations,
 			for (int i = 0; i < match.length; i++) {
 				if (!match[i]) {
 					skip[i] = true;
+					candidates[i] = null;
 					skipped = true;
 				}
 			}

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

@@ -29,6 +29,7 @@
 import java.util.TreeMap;
 
 import org.springframework.beans.factory.BeanFactory;
+import org.springframework.beans.factory.config.ConfigurableBeanFactory;
 import org.springframework.beans.factory.config.ConfigurableListableBeanFactory;
 import org.springframework.context.annotation.Condition;
 import org.springframework.context.annotation.ConditionContext;
@@ -159,6 +160,20 @@ public ConditionEvaluationReport getParent() {
 		return this.parent;
 	}
 
+	/**
+	 * Attempt to find the {@link ConditionEvaluationReport} for the specified bean
+	 * factory.
+	 * @param beanFactory the bean factory (may be {@code null})
+	 * @return the {@link ConditionEvaluationReport} or {@code null}
+	 */
+	public static ConditionEvaluationReport find(BeanFactory beanFactory) {
+		if (beanFactory != null && beanFactory instanceof ConfigurableBeanFactory) {
+			return ConditionEvaluationReport
+					.get((ConfigurableListableBeanFactory) beanFactory);
+		}
+		return null;
+	}
+
 	/**
 	 * Obtain a {@link ConditionEvaluationReport} for the specified bean factory.
 	 * @param beanFactory the bean factory

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

@@ -0,0 +1,147 @@
+/*
+ * Copyright 2012-2018 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.boot.autoconfigure.condition;
+
+import java.util.ArrayList;
+import java.util.Collection;
+import java.util.Collections;
+import java.util.List;
+
+import org.springframework.beans.BeansException;
+import org.springframework.beans.factory.BeanClassLoaderAware;
+import org.springframework.beans.factory.BeanFactory;
+import org.springframework.beans.factory.BeanFactoryAware;
+import org.springframework.boot.autoconfigure.AutoConfigurationImportFilter;
+import org.springframework.boot.autoconfigure.AutoConfigurationMetadata;
+import org.springframework.util.ClassUtils;
+import org.springframework.util.CollectionUtils;
+
+/**
+ * Abstract base class for a {@link SpringBootCondition} that also implements
+ * {@link AutoConfigurationImportFilter}.
+ *
+ * @author Phillip Webb
+ */
+abstract class FilteringSpringBootCondition extends SpringBootCondition
+		implements AutoConfigurationImportFilter, BeanFactoryAware, BeanClassLoaderAware {
+
+	private BeanFactory beanFactory;
+
+	private ClassLoader beanClassLoader;
+
+	@Override
+	public boolean[] match(String[] autoConfigurationClasses,
+			AutoConfigurationMetadata autoConfigurationMetadata) {
+		ConditionEvaluationReport report = ConditionEvaluationReport
+				.find(this.beanFactory);
+		ConditionOutcome[] outcomes = getOutcomes(autoConfigurationClasses,
+				autoConfigurationMetadata);
+		boolean[] match = new boolean[outcomes.length];
+		for (int i = 0; i < outcomes.length; i++) {
+			match[i] = (outcomes[i] == null || outcomes[i].isMatch());
+			if (!match[i] && outcomes[i] != null) {
+				logOutcome(autoConfigurationClasses[i], outcomes[i]);
+				if (report != null) {
+					report.recordConditionEvaluation(autoConfigurationClasses[i], this,
+							outcomes[i]);
+				}
+			}
+		}
+		return match;
+	}
+
+	protected abstract ConditionOutcome[] getOutcomes(String[] autoConfigurationClasses,
+			AutoConfigurationMetadata autoConfigurationMetadata);
+
+	@Override
+	public void setBeanFactory(BeanFactory beanFactory) throws BeansException {
+		this.beanFactory = beanFactory;
+	}
+
+	protected final BeanFactory getBeanFactory() {
+		return this.beanFactory;
+	}
+
+	protected final ClassLoader getBeanClassLoader() {
+		return this.beanClassLoader;
+	}
+
+	@Override
+	public void setBeanClassLoader(ClassLoader classLoader) {
+		this.beanClassLoader = classLoader;
+	}
+
+	protected List<String> filter(Collection<String> classNames,
+			ClassNameFilter classNameFilter, ClassLoader classLoader) {
+		if (CollectionUtils.isEmpty(classNames)) {
+			return Collections.emptyList();
+		}
+		List<String> matches = new ArrayList<>(classNames.size());
+		for (String candidate : classNames) {
+			if (classNameFilter.matches(candidate, classLoader)) {
+				matches.add(candidate);
+			}
+		}
+		return matches;
+	}
+
+	protected enum ClassNameFilter {
+
+		PRESENT {
+
+			@Override
+			public boolean matches(String className, ClassLoader classLoader) {
+				return isPresent(className, classLoader);
+			}
+
+		},
+
+		MISSING {
+
+			@Override
+			public boolean matches(String className, ClassLoader classLoader) {
+				return !isPresent(className, classLoader);
+			}
+
+		};
+
+		public abstract boolean matches(String className, ClassLoader classLoader);
+
+		public static boolean isPresent(String className, ClassLoader classLoader) {
+			if (classLoader == null) {
+				classLoader = ClassUtils.getDefaultClassLoader();
+			}
+			try {
+				forName(className, classLoader);
+				return true;
+			}
+			catch (Throwable ex) {
+				return false;
+			}
+		}
+
+		private static Class<?> forName(String className, ClassLoader classLoader)
+				throws ClassNotFoundException {
+			if (classLoader != null) {
+				return classLoader.loadClass(className);
+			}
+			return Class.forName(className);
+		}
+
+	}
+
+}