Moves BootstrapConfiguration classes to ImportSelector. (#444)

This change moves a dynamic list of classes passed to
`SpringApplicationBuilder.sources` to a `DeferredImportSelector` loaded
by a simple `@Configuration` class. `BootstrapImportSelector` now loads
the classes and orders them and returns the class names so that
`@Conditional` annotations (such as `@ConditionalOnClass`) function
properly.

This was exposed while using java 11.

fixes gh-438

spring-cloud-context/src/main/java/org/springframework/cloud/bootstrap/BootstrapApplicationListener.java

@@ -158,14 +158,6 @@ public class BootstrapApplicationListener
 			}
 			bootstrapProperties.addLast(source);
 		}
-		ClassLoader classLoader = Thread.currentThread().getContextClassLoader();
-		// Use names and ensure unique to protect against duplicates
-		List<String> names = new ArrayList<>(SpringFactoriesLoader
-				.loadFactoryNames(BootstrapConfiguration.class, classLoader));
-		for (String name : StringUtils.commaDelimitedListToStringArray(
-				environment.getProperty("spring.cloud.bootstrap.sources", ""))) {
-			names.add(name);
-		}
 		// TODO: is it possible or sensible to share a ResourceLoader?
 		SpringApplicationBuilder builder = new SpringApplicationBuilder()
 				.profiles(environment.getActiveProfiles()).bannerMode(Mode.OFF)
@@ -192,19 +184,7 @@ public class BootstrapApplicationListener
 			builderApplication
 					.setListeners(filterListeners(builderApplication.getListeners()));
 		}
-		List<Class<?>> sources = new ArrayList<>();
-		for (String name : names) {
-			Class<?> cls = ClassUtils.resolveClassName(name, null);
-			try {
-				cls.getDeclaredAnnotations();
-			}
-			catch (Exception e) {
-				continue;
-			}
-			sources.add(cls);
-		}
-		AnnotationAwareOrderComparator.sort(sources);
-		builder.sources(sources.toArray(new Class[sources.size()]));
+		builder.sources(BootstrapImportSelectorConfiguration.class);
 		final ConfigurableApplicationContext context = builder.run();
 		// gh-214 using spring.application.name=bootstrap to set the context id via
 		// `ContextIdApplicationContextInitializer` prevents apps from getting the actual

spring-cloud-context/src/main/java/org/springframework/cloud/bootstrap/BootstrapImportSelector.java

@@ -0,0 +1,78 @@
+/*
+ * Copyright 2013-2018 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.cloud.bootstrap;
+
+import java.util.ArrayList;
+import java.util.Arrays;
+import java.util.List;
+import java.util.stream.Collectors;
+
+import org.springframework.context.EnvironmentAware;
+import org.springframework.context.annotation.DeferredImportSelector;
+import org.springframework.core.annotation.AnnotationAwareOrderComparator;
+import org.springframework.core.env.Environment;
+import org.springframework.core.io.support.SpringFactoriesLoader;
+import org.springframework.core.type.AnnotationMetadata;
+import org.springframework.util.ClassUtils;
+import org.springframework.util.StringUtils;
+
+/**
+ * This class uses {@link SpringFactoriesLoader} to load {@link BootstrapConfiguration}
+ * entries from {@code spring.factories}. The classes are then loaded so they can
+ * be sorted using {@link AnnotationAwareOrderComparator#sort(List)}.
+ * This class is a {@link DeferredImportSelector} so {@code @Conditional} annotations
+ * on imported classes are supported.
+ */
+public class BootstrapImportSelector implements EnvironmentAware, DeferredImportSelector {
+
+	private Environment environment;
+
+	@Override
+	public void setEnvironment(Environment environment) {
+		this.environment = environment;
+	}
+
+	@Override
+	public String[] selectImports(AnnotationMetadata metadata) {
+		ClassLoader classLoader = Thread.currentThread().getContextClassLoader();
+		// Use names and ensure unique to protect against duplicates
+		List<String> names = new ArrayList<>(SpringFactoriesLoader
+				.loadFactoryNames(BootstrapConfiguration.class, classLoader));
+		names.addAll(Arrays.asList(StringUtils.commaDelimitedListToStringArray(
+				environment.getProperty("spring.cloud.bootstrap.sources", ""))));
+
+		List<Class<?>> sources = new ArrayList<>();
+		for (String name : names) {
+			Class<?> cls = ClassUtils.resolveClassName(name, null);
+			try {
+				cls.getDeclaredAnnotations();
+			}
+			catch (Exception e) {
+				continue;
+			}
+			sources.add(cls);
+		}
+		AnnotationAwareOrderComparator.sort(sources);
+
+		List<String> classNames = sources.stream()
+				.map(Class::getName)
+				.collect(Collectors.toList());
+
+
+		return classNames.toArray(new String[0]);
+	}
+}

spring-cloud-context/src/main/java/org/springframework/cloud/bootstrap/BootstrapImportSelectorConfiguration.java

@@ -0,0 +1,25 @@
+/*
+ * Copyright 2013-2018 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.cloud.bootstrap;
+
+import org.springframework.context.annotation.Configuration;
+import org.springframework.context.annotation.Import;
+
+@Configuration
+@Import(BootstrapImportSelector.class)
+public class BootstrapImportSelectorConfiguration {
+}