Automatically exclude auto-configurations from component scan

Previously, if an auto-configuration class was (wrongly) located in a
candidate package for component scanning, the class was silently loaded
as an app configuration (i.e. with the wrong lifecycle).

This commit adds an `AutoConfigurationExcludeFilter` to
`@SpringBootApplication` so that such classes are automatically
filtered. Since they are registered in `spring.factories`, we can
silently ignore them since we know they'll be loaded later on.

Closes gh-7168

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

@@ -0,0 +1,71 @@
+/*
+ * Copyright 2012-2016 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 java.io.IOException;
+import java.util.List;
+
+import org.springframework.beans.factory.BeanClassLoaderAware;
+import org.springframework.context.annotation.Configuration;
+import org.springframework.core.io.support.SpringFactoriesLoader;
+import org.springframework.core.type.classreading.MetadataReader;
+import org.springframework.core.type.classreading.MetadataReaderFactory;
+import org.springframework.core.type.filter.TypeFilter;
+
+/**
+ * A {@link TypeFilter} implementation that matches registered auto-configuration
+ * classes.
+ *
+ * @author Stephane Nicoll
+ * @since 1.5.0
+ */
+public class AutoConfigurationExcludeFilter implements TypeFilter, BeanClassLoaderAware {
+
+	private ClassLoader beanClassLoader;
+
+	private List<String> candidateAutoConfigurations;
+
+	@Override
+	public void setBeanClassLoader(ClassLoader beanClassLoader) {
+		this.beanClassLoader = beanClassLoader;
+	}
+
+	@Override
+	public boolean match(MetadataReader metadataReader,
+			MetadataReaderFactory metadataReaderFactory) throws IOException {
+		return isConfiguration(metadataReader) && isAutoConfiguration(metadataReader);
+	}
+
+	protected List<String> getCandidateAutoConfigurations() {
+		if (this.candidateAutoConfigurations == null) {
+			this.candidateAutoConfigurations = SpringFactoriesLoader.loadFactoryNames(
+					EnableAutoConfiguration.class, this.beanClassLoader);
+		}
+		return this.candidateAutoConfigurations;
+	}
+
+	private boolean isConfiguration(MetadataReader metadataReader) {
+		return metadataReader.getAnnotationMetadata()
+				.isAnnotated(Configuration.class.getName());
+	}
+
+	private boolean isAutoConfiguration(MetadataReader metadataReader) {
+		return getCandidateAutoConfigurations().contains(
+				metadataReader.getClassMetadata().getClassName());
+	}
+
+}

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

@@ -49,7 +49,9 @@ import org.springframework.core.annotation.AliasFor;
 @Inherited
 @SpringBootConfiguration
 @EnableAutoConfiguration
-@ComponentScan(excludeFilters = @Filter(type = FilterType.CUSTOM, classes = TypeExcludeFilter.class))
+@ComponentScan(excludeFilters = {
+		@Filter(type = FilterType.CUSTOM, classes = TypeExcludeFilter.class),
+		@Filter(type = FilterType.CUSTOM, classes = AutoConfigurationExcludeFilter.class) })
 public @interface SpringBootApplication {
 
 	/**