Add EnvironmentPostProcessorsFactory

Update `EnvironmentPostProcessorApplicationListener` so that it can
either use values from `spring.factories` or use a factory interface.

Closes gh-22529

spring-boot-project/spring-boot-devtools/src/main/java/org/springframework/boot/devtools/RemoteSpringApplication.java

@@ -33,6 +33,7 @@ import org.springframework.boot.devtools.restart.RestartInitializer;
 import org.springframework.boot.devtools.restart.RestartScopeInitializer;
 import org.springframework.boot.devtools.restart.Restarter;
 import org.springframework.boot.env.EnvironmentPostProcessorApplicationListener;
+import org.springframework.boot.env.EnvironmentPostProcessorsFactory;
 import org.springframework.context.ApplicationContextInitializer;
 import org.springframework.context.ApplicationListener;
 import org.springframework.core.io.ClassPathResource;
@@ -72,7 +73,8 @@ public final class RemoteSpringApplication {
 	private Collection<ApplicationListener<?>> getListeners() {
 		List<ApplicationListener<?>> listeners = new ArrayList<>();
 		listeners.add(new AnsiOutputApplicationListener());
-		listeners.add(new EnvironmentPostProcessorApplicationListener(ConfigDataEnvironmentPostProcessor.class));
+		listeners.add(new EnvironmentPostProcessorApplicationListener(
+				EnvironmentPostProcessorsFactory.singleton(ConfigDataEnvironmentPostProcessor::new)));
 		listeners.add(new ClasspathLoggingApplicationListener());
 		listeners.add(new LoggingApplicationListener());
 		listeners.add(new RemoteUrlPropertyExtractor());

spring-boot-project/spring-boot/src/main/java/org/springframework/boot/env/EnvironmentPostProcessorApplicationListener.java

@@ -16,29 +16,17 @@
 
 package org.springframework.boot.env;
 
-import java.lang.reflect.Constructor;
-import java.util.ArrayList;
-import java.util.Arrays;
 import java.util.List;
-import java.util.stream.Collectors;
-
-import org.apache.commons.logging.Log;
 
 import org.springframework.boot.SpringApplication;
 import org.springframework.boot.context.event.ApplicationEnvironmentPreparedEvent;
 import org.springframework.boot.context.event.ApplicationFailedEvent;
 import org.springframework.boot.context.event.ApplicationPreparedEvent;
-import org.springframework.boot.logging.DeferredLogFactory;
 import org.springframework.boot.logging.DeferredLogs;
 import org.springframework.context.ApplicationEvent;
 import org.springframework.context.event.SmartApplicationListener;
 import org.springframework.core.Ordered;
-import org.springframework.core.annotation.AnnotationAwareOrderComparator;
 import org.springframework.core.env.ConfigurableEnvironment;
-import org.springframework.core.io.support.SpringFactoriesLoader;
-import org.springframework.util.Assert;
-import org.springframework.util.ClassUtils;
-import org.springframework.util.ReflectionUtils;
 
 /**
  * {@link SmartApplicationListener} used to trigger {@link EnvironmentPostProcessor
@@ -54,46 +42,34 @@ public class EnvironmentPostProcessorApplicationListener implements SmartApplica
 	 */
 	public static final int DEFAULT_ORDER = Ordered.HIGHEST_PRECEDENCE + 10;
 
-	private final DeferredLogs deferredLogs = new DeferredLogs();
+	private final DeferredLogs deferredLogs;
 
 	private int order = DEFAULT_ORDER;
 
-	private final List<String> postProcessorClassNames;
+	private EnvironmentPostProcessorsFactory postProcessorsFactory;
 
 	/**
 	 * Create a new {@link EnvironmentPostProcessorApplicationListener} with
 	 * {@link EnvironmentPostProcessor} classes loaded via {@code spring.factories}.
 	 */
 	public EnvironmentPostProcessorApplicationListener() {
-		this(SpringFactoriesLoader.loadFactoryNames(EnvironmentPostProcessor.class,
-				EnvironmentPostProcessorApplicationListener.class.getClassLoader()));
+		this(EnvironmentPostProcessorsFactory
+				.fromSpringFactories(EnvironmentPostProcessorApplicationListener.class.getClassLoader()));
 	}
 
 	/**
-	 * Create a new {@link EnvironmentPostProcessorApplicationListener} with the specified
-	 * {@link EnvironmentPostProcessor} classes.
-	 * @param postProcessorClasses the environment post processor classes
+	 * Create a new {@link EnvironmentPostProcessorApplicationListener} with post
+	 * processors created by the given factory.
+	 * @param postProcessorsFactory the post processors factory
 	 */
-	public EnvironmentPostProcessorApplicationListener(Class<?>... postProcessorClasses) {
-		this(Arrays.stream(postProcessorClasses).map(Class::getName).collect(Collectors.toList()));
+	public EnvironmentPostProcessorApplicationListener(EnvironmentPostProcessorsFactory postProcessorsFactory) {
+		this(postProcessorsFactory, new DeferredLogs());
 	}
 
-	/**
-	 * Create a new {@link EnvironmentPostProcessorApplicationListener} with the specified
-	 * {@link EnvironmentPostProcessor} class names.
-	 * @param postProcessorClassNames the environment post processor class names
-	 */
-	public EnvironmentPostProcessorApplicationListener(String... postProcessorClassNames) {
-		this(Arrays.asList(postProcessorClassNames));
-	}
-
-	/**
-	 * Create a new {@link EnvironmentPostProcessorApplicationListener} with the specified
-	 * {@link EnvironmentPostProcessor} class names.
-	 * @param postProcessorClassNames the environment post processor class names
-	 */
-	public EnvironmentPostProcessorApplicationListener(List<String> postProcessorClassNames) {
-		this.postProcessorClassNames = postProcessorClassNames;
+	EnvironmentPostProcessorApplicationListener(EnvironmentPostProcessorsFactory postProcessorsFactory,
+			DeferredLogs deferredLogs) {
+		this.postProcessorsFactory = postProcessorsFactory;
+		this.deferredLogs = deferredLogs;
 	}
 
 	@Override
@@ -108,64 +84,24 @@ public class EnvironmentPostProcessorApplicationListener implements SmartApplica
 		if (event instanceof ApplicationEnvironmentPreparedEvent) {
 			onApplicationEnvironmentPreparedEvent((ApplicationEnvironmentPreparedEvent) event);
 		}
-		if (event instanceof ApplicationPreparedEvent) {
-			onApplicationPreparedEvent((ApplicationPreparedEvent) event);
+		if (event instanceof ApplicationPreparedEvent || event instanceof ApplicationFailedEvent) {
+			onFinish();
 		}
 	}
 
 	private void onApplicationEnvironmentPreparedEvent(ApplicationEnvironmentPreparedEvent event) {
 		ConfigurableEnvironment environment = event.getEnvironment();
 		SpringApplication application = event.getSpringApplication();
-		List<EnvironmentPostProcessor> postProcessors = loadPostProcessors(event.getSpringApplication());
-		for (EnvironmentPostProcessor postProcessor : postProcessors) {
+		for (EnvironmentPostProcessor postProcessor : getEnvironmentPostProcessors()) {
 			postProcessor.postProcessEnvironment(environment, application);
 		}
 	}
 
-	private List<EnvironmentPostProcessor> loadPostProcessors(SpringApplication application) {
-		return loadPostProcessors(application, this.postProcessorClassNames);
+	List<EnvironmentPostProcessor> getEnvironmentPostProcessors() {
+		return this.postProcessorsFactory.getEnvironmentPostProcessors(this.deferredLogs);
 	}
 
-	private List<EnvironmentPostProcessor> loadPostProcessors(SpringApplication application, List<String> names) {
-		List<EnvironmentPostProcessor> postProcessors = new ArrayList<>(names.size());
-		for (String name : names) {
-			try {
-				postProcessors.add(instantiatePostProcessor(application, name));
-			}
-			catch (Throwable ex) {
-				throw new IllegalArgumentException("Unable to instantiate factory class [" + name
-						+ "] for factory type [" + EnvironmentPostProcessor.class.getName() + "]", ex);
-			}
-		}
-		AnnotationAwareOrderComparator.sort(postProcessors);
-		return postProcessors;
-	}
-
-	private EnvironmentPostProcessor instantiatePostProcessor(SpringApplication application, String name)
-			throws Exception {
-		Class<?> type = ClassUtils.forName(name, getClass().getClassLoader());
-		Assert.isAssignable(EnvironmentPostProcessor.class, type);
-		Constructor<?>[] constructors = type.getDeclaredConstructors();
-		for (Constructor<?> constructor : constructors) {
-			if (constructor.getParameterCount() == 1) {
-				Class<?> cls = constructor.getParameterTypes()[0];
-				if (DeferredLogFactory.class.isAssignableFrom(cls)) {
-					return newInstance(constructor, this.deferredLogs);
-				}
-				if (Log.class.isAssignableFrom(cls)) {
-					return newInstance(constructor, this.deferredLogs.getLog(type));
-				}
-			}
-		}
-		return (EnvironmentPostProcessor) ReflectionUtils.accessibleConstructor(type).newInstance();
-	}
-
-	private EnvironmentPostProcessor newInstance(Constructor<?> constructor, Object... initargs) throws Exception {
-		ReflectionUtils.makeAccessible(constructor);
-		return (EnvironmentPostProcessor) constructor.newInstance(initargs);
-	}
-
-	private void onApplicationPreparedEvent(ApplicationPreparedEvent event) {
+	private void onFinish() {
 		this.deferredLogs.switchOverAll();
 	}
 

spring-boot-project/spring-boot/src/main/java/org/springframework/boot/env/EnvironmentPostProcessorsFactory.java

@@ -0,0 +1,84 @@
+/*
+ * Copyright 2012-2020 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
+ *
+ *      https://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.env;
+
+import java.util.Collections;
+import java.util.List;
+import java.util.function.Function;
+
+import org.springframework.boot.logging.DeferredLogFactory;
+import org.springframework.core.io.support.SpringFactoriesLoader;
+
+/**
+ * Factory interface used by the {@link EnvironmentPostProcessorApplicationListener} to
+ * create the {@link EnvironmentPostProcessor} instances.
+ *
+ * @author Phillip Webb
+ * @since 2.4.0
+ */
+@FunctionalInterface
+public interface EnvironmentPostProcessorsFactory {
+
+	/**
+	 * Create all requested {@link EnvironmentPostProcessor} instances.
+	 * @param logFactory a deferred log factory
+	 * @return the post processor instances
+	 */
+	List<EnvironmentPostProcessor> getEnvironmentPostProcessors(DeferredLogFactory logFactory);
+
+	/**
+	 * Return a {@link EnvironmentPostProcessorsFactory} backed by
+	 * {@code spring.factories}.
+	 * @param classLoader the source class loader
+	 * @return an {@link EnvironmentPostProcessorsFactory} instance
+	 */
+	static EnvironmentPostProcessorsFactory fromSpringFactories(ClassLoader classLoader) {
+		return new ReflectionEnvironmentPostProcessorsFactory(
+				SpringFactoriesLoader.loadFactoryNames(EnvironmentPostProcessor.class, classLoader));
+	}
+
+	/**
+	 * Return a {@link EnvironmentPostProcessorsFactory} that reflectively creates post
+	 * processors from the given classes.
+	 * @param classes the post processor classes
+	 * @return an {@link EnvironmentPostProcessorsFactory} instance
+	 */
+	static EnvironmentPostProcessorsFactory of(Class<?>... classes) {
+		return new ReflectionEnvironmentPostProcessorsFactory(classes);
+	}
+
+	/**
+	 * Return a {@link EnvironmentPostProcessorsFactory} that reflectively creates post
+	 * processors from the given class names.
+	 * @param classNames the post processor class names
+	 * @return an {@link EnvironmentPostProcessorsFactory} instance
+	 */
+	static EnvironmentPostProcessorsFactory of(String... classNames) {
+		return new ReflectionEnvironmentPostProcessorsFactory(classNames);
+	}
+
+	/**
+	 * Create a {@link EnvironmentPostProcessorsFactory} containing only a single post
+	 * processor.
+	 * @param factory the factory used to create the post processor
+	 * @return an {@link EnvironmentPostProcessorsFactory} instance
+	 */
+	static EnvironmentPostProcessorsFactory singleton(Function<DeferredLogFactory, EnvironmentPostProcessor> factory) {
+		return (logFactory) -> Collections.singletonList(factory.apply(logFactory));
+	}
+
+}

spring-boot-project/spring-boot/src/main/java/org/springframework/boot/env/ReflectionEnvironmentPostProcessorsFactory.java

@@ -0,0 +1,94 @@
+/*
+ * Copyright 2012-2020 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
+ *
+ *      https://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.env;
+
+import java.lang.reflect.Constructor;
+import java.util.ArrayList;
+import java.util.Arrays;
+import java.util.List;
+
+import org.apache.commons.logging.Log;
+
+import org.springframework.boot.logging.DeferredLogFactory;
+import org.springframework.core.annotation.AnnotationAwareOrderComparator;
+import org.springframework.util.Assert;
+import org.springframework.util.ClassUtils;
+import org.springframework.util.ReflectionUtils;
+
+/**
+ * {@link EnvironmentPostProcessorsFactory} implementation that uses reflection to create
+ * instances.
+ *
+ * @author Phillip Webb
+ */
+class ReflectionEnvironmentPostProcessorsFactory implements EnvironmentPostProcessorsFactory {
+
+	private final List<String> classNames;
+
+	ReflectionEnvironmentPostProcessorsFactory(Class<?>... classes) {
+		this(Arrays.stream(classes).map(Class::getName).toArray(String[]::new));
+	}
+
+	ReflectionEnvironmentPostProcessorsFactory(String... classNames) {
+		this(Arrays.asList(classNames));
+	}
+
+	ReflectionEnvironmentPostProcessorsFactory(List<String> classNames) {
+		this.classNames = classNames;
+	}
+
+	@Override
+	public List<EnvironmentPostProcessor> getEnvironmentPostProcessors(DeferredLogFactory logFactory) {
+		List<EnvironmentPostProcessor> postProcessors = new ArrayList<>(this.classNames.size());
+		for (String className : this.classNames) {
+			try {
+				postProcessors.add(getEnvironmentPostProcessor(className, logFactory));
+			}
+			catch (Throwable ex) {
+				throw new IllegalArgumentException("Unable to instantiate factory class [" + className
+						+ "] for factory type [" + EnvironmentPostProcessor.class.getName() + "]", ex);
+			}
+		}
+		AnnotationAwareOrderComparator.sort(postProcessors);
+		return postProcessors;
+	}
+
+	private EnvironmentPostProcessor getEnvironmentPostProcessor(String className, DeferredLogFactory logFactory)
+			throws Exception {
+		Class<?> type = ClassUtils.forName(className, getClass().getClassLoader());
+		Assert.isAssignable(EnvironmentPostProcessor.class, type);
+		Constructor<?>[] constructors = type.getDeclaredConstructors();
+		for (Constructor<?> constructor : constructors) {
+			if (constructor.getParameterCount() == 1) {
+				Class<?> cls = constructor.getParameterTypes()[0];
+				if (DeferredLogFactory.class.isAssignableFrom(cls)) {
+					return newInstance(constructor, logFactory);
+				}
+				if (Log.class.isAssignableFrom(cls)) {
+					return newInstance(constructor, logFactory.getLog(type));
+				}
+			}
+		}
+		return (EnvironmentPostProcessor) ReflectionUtils.accessibleConstructor(type).newInstance();
+	}
+
+	private EnvironmentPostProcessor newInstance(Constructor<?> constructor, Object... initargs) throws Exception {
+		ReflectionUtils.makeAccessible(constructor);
+		return (EnvironmentPostProcessor) constructor.newInstance(initargs);
+	}
+
+}

spring-boot-project/spring-boot/src/test/java/org/springframework/boot/env/EnvironmentPostProcessorApplicationListenerTests.java

@@ -16,8 +16,26 @@
 
 package org.springframework.boot.env;
 
+import java.util.List;
+
 import org.junit.jupiter.api.Test;
 
+import org.springframework.boot.SpringApplication;
+import org.springframework.boot.context.event.ApplicationEnvironmentPreparedEvent;
+import org.springframework.boot.context.event.ApplicationFailedEvent;
+import org.springframework.boot.context.event.ApplicationPreparedEvent;
+import org.springframework.boot.context.event.ApplicationStartingEvent;
+import org.springframework.boot.logging.DeferredLogFactory;
+import org.springframework.boot.logging.DeferredLogs;
+import org.springframework.context.ConfigurableApplicationContext;
+import org.springframework.core.env.ConfigurableEnvironment;
+import org.springframework.mock.env.MockEnvironment;
+
+import static org.assertj.core.api.Assertions.assertThat;
+import static org.mockito.Mockito.mock;
+import static org.mockito.Mockito.spy;
+import static org.mockito.Mockito.verify;
+
 /**
  * Tests for {@link EnvironmentPostProcessorApplicationListener}.
  *
@@ -25,9 +43,85 @@ import org.junit.jupiter.api.Test;
  */
 class EnvironmentPostProcessorApplicationListenerTests {
 
+	private DeferredLogs deferredLogs = spy(new DeferredLogs());
+
+	private EnvironmentPostProcessorApplicationListener listener = new EnvironmentPostProcessorApplicationListener(
+			EnvironmentPostProcessorsFactory.singleton(TestEnvironmentPostProcessor::new), this.deferredLogs);
+
 	@Test
-	void test() {
-		// fail("Not yet implemented");
+	void createUsesSpringFactories() {
+		EnvironmentPostProcessorApplicationListener listener = new EnvironmentPostProcessorApplicationListener();
+		assertThat(listener.getEnvironmentPostProcessors()).hasSizeGreaterThan(1);
+	}
+
+	@Test
+	void createWhenHasFactoryUsesFactory() {
+		EnvironmentPostProcessorApplicationListener listener = new EnvironmentPostProcessorApplicationListener(
+				EnvironmentPostProcessorsFactory.singleton(TestEnvironmentPostProcessor::new));
+		List<EnvironmentPostProcessor> postProcessors = listener.getEnvironmentPostProcessors();
+		assertThat(postProcessors).hasSize(1);
+		assertThat(postProcessors.get(0)).isInstanceOf(TestEnvironmentPostProcessor.class);
+	}
+
+	@Test
+	void supporteEventTypeWhenApplicationEnvironmentPreparedEventReturnsTrue() {
+		assertThat(this.listener.supportsEventType(ApplicationEnvironmentPreparedEvent.class)).isTrue();
+	}
+
+	@Test
+	void supporteEventTypeWhenApplicationPreparedEventReturnsTrue() {
+		assertThat(this.listener.supportsEventType(ApplicationPreparedEvent.class)).isTrue();
+	}
+
+	@Test
+	void supporteEventTypeWhenApplicationFailedEventReturnsTrue() {
+		assertThat(this.listener.supportsEventType(ApplicationFailedEvent.class)).isTrue();
+	}
+
+	@Test
+	void supporteEventTypeWhenOtherEventReturnsFalse() {
+		assertThat(this.listener.supportsEventType(ApplicationStartingEvent.class)).isFalse();
+	}
+
+	@Test
+	void onApplicationEventWhenApplicationEnvironmentPreparedEventCallsPostProcessors() {
+		SpringApplication application = mock(SpringApplication.class);
+		MockEnvironment environment = new MockEnvironment();
+		ApplicationEnvironmentPreparedEvent event = new ApplicationEnvironmentPreparedEvent(application, new String[0],
+				environment);
+		this.listener.onApplicationEvent(event);
+		assertThat(environment.getProperty("processed")).isEqualTo("true");
+	}
+
+	@Test
+	void onApplicationEventWhenApplicationPreparedEventSwitchesLogs() {
+		SpringApplication application = mock(SpringApplication.class);
+		ConfigurableApplicationContext context = mock(ConfigurableApplicationContext.class);
+		ApplicationPreparedEvent event = new ApplicationPreparedEvent(application, new String[0], context);
+		this.listener.onApplicationEvent(event);
+		verify(this.deferredLogs).switchOverAll();
+	}
+
+	@Test
+	void onApplicationEventWhenApplicationFailedEventSwitchesLogs() {
+		SpringApplication application = mock(SpringApplication.class);
+		ConfigurableApplicationContext context = mock(ConfigurableApplicationContext.class);
+		ApplicationFailedEvent event = new ApplicationFailedEvent(application, new String[0], context,
+				new RuntimeException());
+		this.listener.onApplicationEvent(event);
+		verify(this.deferredLogs).switchOverAll();
+	}
+
+	static class TestEnvironmentPostProcessor implements EnvironmentPostProcessor {
+
+		TestEnvironmentPostProcessor(DeferredLogFactory logFactory) {
+		}
+
+		@Override
+		public void postProcessEnvironment(ConfigurableEnvironment environment, SpringApplication application) {
+			((MockEnvironment) environment).setProperty("processed", "true");
+		}
+
 	}
 
 }

spring-boot-project/spring-boot/src/test/java/org/springframework/boot/env/EnvironmentPostProcessorsFactoryTests.java

@@ -0,0 +1,84 @@
+/*
+ * Copyright 2012-2020 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
+ *
+ *      https://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.env;
+
+import java.util.List;
+import java.util.function.Supplier;
+
+import org.junit.jupiter.api.Test;
+
+import org.springframework.boot.SpringApplication;
+import org.springframework.boot.logging.DeferredLogFactory;
+import org.springframework.core.env.ConfigurableEnvironment;
+
+import static org.assertj.core.api.Assertions.assertThat;
+
+/**
+ * Tests for {@link EnvironmentPostProcessorsFactory}.
+ *
+ * @author Phillip Webb
+ */
+class EnvironmentPostProcessorsFactoryTests {
+
+	private final DeferredLogFactory logFactory = Supplier::get;
+
+	@Test
+	void fromSpringFactoriesReturnsFactory() {
+		EnvironmentPostProcessorsFactory factory = EnvironmentPostProcessorsFactory.fromSpringFactories(null);
+		List<EnvironmentPostProcessor> processors = factory.getEnvironmentPostProcessors(this.logFactory);
+		assertThat(processors).hasSizeGreaterThan(1);
+	}
+
+	@Test
+	void ofClassesReturnsFactory() {
+		EnvironmentPostProcessorsFactory factory = EnvironmentPostProcessorsFactory
+				.of(TestEnvironmentPostProcessor.class);
+		List<EnvironmentPostProcessor> processors = factory.getEnvironmentPostProcessors(this.logFactory);
+		assertThat(processors).hasSize(1);
+		assertThat(processors.get(0)).isInstanceOf(TestEnvironmentPostProcessor.class);
+	}
+
+	@Test
+	void ofClassNamesReturnsFactory() {
+		EnvironmentPostProcessorsFactory factory = EnvironmentPostProcessorsFactory
+				.of(TestEnvironmentPostProcessor.class.getName());
+		List<EnvironmentPostProcessor> processors = factory.getEnvironmentPostProcessors(this.logFactory);
+		assertThat(processors).hasSize(1);
+		assertThat(processors.get(0)).isInstanceOf(TestEnvironmentPostProcessor.class);
+	}
+
+	@Test
+	void singletonReturnsFactory() {
+		EnvironmentPostProcessorsFactory factory = EnvironmentPostProcessorsFactory
+				.singleton(TestEnvironmentPostProcessor::new);
+		List<EnvironmentPostProcessor> processors = factory.getEnvironmentPostProcessors(this.logFactory);
+		assertThat(processors).hasSize(1);
+		assertThat(processors.get(0)).isInstanceOf(TestEnvironmentPostProcessor.class);
+	}
+
+	static class TestEnvironmentPostProcessor implements EnvironmentPostProcessor {
+
+		TestEnvironmentPostProcessor(DeferredLogFactory logFactory) {
+		}
+
+		@Override
+		public void postProcessEnvironment(ConfigurableEnvironment environment, SpringApplication application) {
+		}
+
+	}
+
+}

spring-boot-project/spring-boot/src/test/java/org/springframework/boot/env/ReflectionEnvironmentPostProcessorsFactoryTests.java

@@ -0,0 +1,157 @@
+/*
+ * Copyright 2012-2020 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
+ *
+ *      https://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.env;
+
+import java.io.InputStream;
+import java.util.Arrays;
+import java.util.List;
+import java.util.function.Supplier;
+
+import org.apache.commons.logging.Log;
+import org.junit.jupiter.api.Test;
+
+import org.springframework.boot.SpringApplication;
+import org.springframework.boot.logging.DeferredLogFactory;
+import org.springframework.core.env.ConfigurableEnvironment;
+
+import static org.assertj.core.api.Assertions.assertThat;
+import static org.assertj.core.api.Assertions.assertThatIllegalArgumentException;
+
+/**
+ * Tests for {@link ReflectionEnvironmentPostProcessorsFactory}.
+ *
+ * @author Phillip Webb
+ */
+class ReflectionEnvironmentPostProcessorsFactoryTests {
+
+	private final DeferredLogFactory logFactory = Supplier::get;
+
+	@Test
+	void createWithClassesCreatesFactory() {
+		ReflectionEnvironmentPostProcessorsFactory factory = new ReflectionEnvironmentPostProcessorsFactory(
+				TestEnvironmentPostProcessor.class);
+		assertThatFactory(factory).createsSinglePostProcessor(TestEnvironmentPostProcessor.class);
+	}
+
+	@Test
+	void createWithClassNamesArrayCreatesFactory() {
+		ReflectionEnvironmentPostProcessorsFactory factory = new ReflectionEnvironmentPostProcessorsFactory(
+				TestEnvironmentPostProcessor.class.getName());
+		assertThatFactory(factory).createsSinglePostProcessor(TestEnvironmentPostProcessor.class);
+	}
+
+	@Test
+	void createWithClassNamesListCreatesFactory() {
+		ReflectionEnvironmentPostProcessorsFactory factory = new ReflectionEnvironmentPostProcessorsFactory(
+				Arrays.asList(TestEnvironmentPostProcessor.class.getName()));
+		assertThatFactory(factory).createsSinglePostProcessor(TestEnvironmentPostProcessor.class);
+	}
+
+	@Test
+	void getEnvironmentPostProcessorsWhenHasDefaultConstructorCreatesPostProcessors() {
+		ReflectionEnvironmentPostProcessorsFactory factory = new ReflectionEnvironmentPostProcessorsFactory(
+				TestEnvironmentPostProcessor.class.getName());
+		assertThatFactory(factory).createsSinglePostProcessor(TestEnvironmentPostProcessor.class);
+	}
+
+	@Test
+	void getEnvironmentPostProcessorsWhenHasLogFactoryConstructorCreatesPostProcessors() {
+		ReflectionEnvironmentPostProcessorsFactory factory = new ReflectionEnvironmentPostProcessorsFactory(
+				TestLogFactoryEnvironmentPostProcessor.class.getName());
+		assertThatFactory(factory).createsSinglePostProcessor(TestLogFactoryEnvironmentPostProcessor.class);
+	}
+
+	@Test
+	void getEnvironmentPostProcessorsWhenHasLogConstructorCreatesPostProcessors() {
+		ReflectionEnvironmentPostProcessorsFactory factory = new ReflectionEnvironmentPostProcessorsFactory(
+				TestLogEnvironmentPostProcessor.class.getName());
+		assertThatFactory(factory).createsSinglePostProcessor(TestLogEnvironmentPostProcessor.class);
+	}
+
+	@Test
+	void getEnvironmentPostProcessorsWhenHasNoSuitableConstructorThrowsException() {
+		ReflectionEnvironmentPostProcessorsFactory factory = new ReflectionEnvironmentPostProcessorsFactory(
+				BadEnvironmentPostProcessor.class.getName());
+		assertThatIllegalArgumentException().isThrownBy(() -> factory.getEnvironmentPostProcessors(this.logFactory))
+				.withMessageContaining("Unable to instantiate");
+	}
+
+	private EnvironmentPostProcessorsFactoryAssert assertThatFactory(EnvironmentPostProcessorsFactory factory) {
+		return new EnvironmentPostProcessorsFactoryAssert(factory);
+	}
+
+	class EnvironmentPostProcessorsFactoryAssert {
+
+		private EnvironmentPostProcessorsFactory factory;
+
+		EnvironmentPostProcessorsFactoryAssert(EnvironmentPostProcessorsFactory factory) {
+			this.factory = factory;
+		}
+
+		void createsSinglePostProcessor(Class<?> expectedType) {
+			List<EnvironmentPostProcessor> processors = this.factory
+					.getEnvironmentPostProcessors(ReflectionEnvironmentPostProcessorsFactoryTests.this.logFactory);
+			assertThat(processors).hasSize(1);
+			assertThat(processors.get(0)).isInstanceOf(expectedType);
+		}
+
+	}
+
+	static class TestEnvironmentPostProcessor implements EnvironmentPostProcessor {
+
+		@Override
+		public void postProcessEnvironment(ConfigurableEnvironment environment, SpringApplication application) {
+		}
+
+	}
+
+	static class TestLogFactoryEnvironmentPostProcessor implements EnvironmentPostProcessor {
+
+		TestLogFactoryEnvironmentPostProcessor(DeferredLogFactory logFactory) {
+			assertThat(logFactory).isNotNull();
+		}
+
+		@Override
+		public void postProcessEnvironment(ConfigurableEnvironment environment, SpringApplication application) {
+		}
+
+	}
+
+	static class TestLogEnvironmentPostProcessor implements EnvironmentPostProcessor {
+
+		TestLogEnvironmentPostProcessor(Log log) {
+			assertThat(log).isNotNull();
+		}
+
+		@Override
+		public void postProcessEnvironment(ConfigurableEnvironment environment, SpringApplication application) {
+		}
+
+	}
+
+	static class BadEnvironmentPostProcessor implements EnvironmentPostProcessor {
+
+		BadEnvironmentPostProcessor(InputStream inputStream) {
+		}
+
+		@Override
+		public void postProcessEnvironment(ConfigurableEnvironment environment, SpringApplication application) {
+		}
+
+	}
+
+}