Add ConfigDataEnvironmentUpdateListener support

Add an overloaded `ConfigDataEnvironmentPostProcessor.applyTo` method
that accepts a listener that can used to track the updates that were
applied to the `Environment`.

The listener can be used to track the which `ConfigDataLocation` and
the `ConfigDataResource` were used to add a `PropertySource`. The lister
can also be used to tell which profiles were applied.

This enhancement is being added in a patch release because it's will
be useful for Spring Cloud 2020.0.0.

Closes gh-24504

spring-boot-project/spring-boot/src/main/java/org/springframework/boot/context/config/ConfigDataEnvironment.java

@@ -119,6 +119,8 @@ class ConfigDataEnvironment {
 
 	private final Collection<String> additionalProfiles;
 
+	private final ConfigDataEnvironmentUpdateListener environmentUpdateListener;
+
 	private final ConfigDataLoaders loaders;
 
 	private final ConfigDataEnvironmentContributors contributors;
@@ -130,9 +132,13 @@ class ConfigDataEnvironment {
 	 * @param environment the Spring {@link Environment}.
 	 * @param resourceLoader {@link ResourceLoader} to load resource locations
 	 * @param additionalProfiles any additional profiles to activate
+	 * @param environmentUpdateListener optional
+	 * {@link ConfigDataEnvironmentUpdateListener} that can be used to track
+	 * {@link Environment} updates.
 	 */
 	ConfigDataEnvironment(DeferredLogFactory logFactory, ConfigurableBootstrapContext bootstrapContext,
-			ConfigurableEnvironment environment, ResourceLoader resourceLoader, Collection<String> additionalProfiles) {
+			ConfigurableEnvironment environment, ResourceLoader resourceLoader, Collection<String> additionalProfiles,
+			ConfigDataEnvironmentUpdateListener environmentUpdateListener) {
 		Binder binder = Binder.get(environment);
 		UseLegacyConfigProcessingException.throwIfRequested(binder);
 		this.logFactory = logFactory;
@@ -143,6 +149,8 @@ class ConfigDataEnvironment {
 		this.environment = environment;
 		this.resolvers = createConfigDataLocationResolvers(logFactory, bootstrapContext, binder, resourceLoader);
 		this.additionalProfiles = additionalProfiles;
+		this.environmentUpdateListener = (environmentUpdateListener != null) ? environmentUpdateListener
+				: ConfigDataEnvironmentUpdateListener.NONE;
 		this.loaders = new ConfigDataLoaders(logFactory, bootstrapContext);
 		this.contributors = createContributors(binder);
 	}
@@ -301,16 +309,18 @@ private void applyToEnvironment(ConfigDataEnvironmentContributors contributors,
 		MutablePropertySources propertySources = this.environment.getPropertySources();
 		this.logger.trace("Applying config data environment contributions");
 		for (ConfigDataEnvironmentContributor contributor : contributors) {
-			if (contributor.getKind() == ConfigDataEnvironmentContributor.Kind.BOUND_IMPORT
-					&& contributor.getPropertySource() != null) {
+			PropertySource<?> propertySource = contributor.getPropertySource();
+			if (contributor.getKind() == ConfigDataEnvironmentContributor.Kind.BOUND_IMPORT && propertySource != null) {
 				if (!contributor.isActive(activationContext)) {
-					this.logger.trace(LogMessage.format("Skipping inactive property source '%s'",
-							contributor.getPropertySource().getName()));
+					this.logger.trace(
+							LogMessage.format("Skipping inactive property source '%s'", propertySource.getName()));
 				}
 				else {
-					this.logger.trace(LogMessage.format("Adding imported property source '%s'",
-							contributor.getPropertySource().getName()));
-					propertySources.addLast(contributor.getPropertySource());
+					this.logger
+							.trace(LogMessage.format("Adding imported property source '%s'", propertySource.getName()));
+					propertySources.addLast(propertySource);
+					this.environmentUpdateListener.onPropertySourceAdded(propertySource, contributor.getLocation(),
+							contributor.getResource());
 				}
 			}
 		}
@@ -320,6 +330,7 @@ private void applyToEnvironment(ConfigDataEnvironmentContributors contributors,
 		this.environment.setDefaultProfiles(StringUtils.toStringArray(profiles.getDefault()));
 		this.logger.trace(LogMessage.format("Setting active profiles: %s", profiles.getActive()));
 		this.environment.setActiveProfiles(StringUtils.toStringArray(profiles.getActive()));
+		this.environmentUpdateListener.onSetProfiles(profiles);
 	}
 
 	private void checkForInvalidProperties(ConfigDataEnvironmentContributors contributors) {

spring-boot-project/spring-boot/src/main/java/org/springframework/boot/context/config/ConfigDataEnvironmentPostProcessor.java

@@ -63,11 +63,20 @@ public class ConfigDataEnvironmentPostProcessor implements EnvironmentPostProces
 
 	private final ConfigurableBootstrapContext bootstrapContext;
 
+	private final ConfigDataEnvironmentUpdateListener environmentUpdateListener;
+
 	public ConfigDataEnvironmentPostProcessor(DeferredLogFactory logFactory,
 			ConfigurableBootstrapContext bootstrapContext) {
+		this(logFactory, bootstrapContext, null);
+	}
+
+	public ConfigDataEnvironmentPostProcessor(DeferredLogFactory logFactory,
+			ConfigurableBootstrapContext bootstrapContext,
+			ConfigDataEnvironmentUpdateListener environmentUpdateListener) {
 		this.logFactory = logFactory;
 		this.logger = logFactory.getLog(getClass());
 		this.bootstrapContext = bootstrapContext;
+		this.environmentUpdateListener = environmentUpdateListener;
 	}
 
 	@Override
@@ -97,7 +106,7 @@ void postProcessEnvironment(ConfigurableEnvironment environment, ResourceLoader
 	ConfigDataEnvironment getConfigDataEnvironment(ConfigurableEnvironment environment, ResourceLoader resourceLoader,
 			Collection<String> additionalProfiles) {
 		return new ConfigDataEnvironment(this.logFactory, this.bootstrapContext, environment, resourceLoader,
-				additionalProfiles);
+				additionalProfiles, this.environmentUpdateListener);
 	}
 
 	private void postProcessUsingLegacyApplicationListener(ConfigurableEnvironment environment,
@@ -154,6 +163,29 @@ public static void applyTo(ConfigurableEnvironment environment, ResourceLoader r
 		postProcessor.postProcessEnvironment(environment, resourceLoader, additionalProfiles);
 	}
 
+	/**
+	 * Apply {@link ConfigData} post-processing to an existing {@link Environment}. This
+	 * method can be useful when working with an {@link Environment} that has been created
+	 * directly and not necessarily as part of a {@link SpringApplication}.
+	 * @param environment the environment to apply {@link ConfigData} to
+	 * @param resourceLoader the resource loader to use
+	 * @param bootstrapContext the bootstrap context to use or {@code null} to use a
+	 * throw-away context
+	 * @param additionalProfiles any additional profiles that should be applied
+	 * @param environmentUpdateListener optional
+	 * {@link ConfigDataEnvironmentUpdateListener} that can be used to track
+	 * {@link Environment} updates.
+	 */
+	public static void applyTo(ConfigurableEnvironment environment, ResourceLoader resourceLoader,
+			ConfigurableBootstrapContext bootstrapContext, Collection<String> additionalProfiles,
+			ConfigDataEnvironmentUpdateListener environmentUpdateListener) {
+		DeferredLogFactory logFactory = Supplier::get;
+		bootstrapContext = (bootstrapContext != null) ? bootstrapContext : new DefaultBootstrapContext();
+		ConfigDataEnvironmentPostProcessor postProcessor = new ConfigDataEnvironmentPostProcessor(logFactory,
+				bootstrapContext, environmentUpdateListener);
+		postProcessor.postProcessEnvironment(environment, resourceLoader, additionalProfiles);
+	}
+
 	@SuppressWarnings("deprecation")
 	static class LegacyConfigFileApplicationListener extends ConfigFileApplicationListener {
 

spring-boot-project/spring-boot/src/main/java/org/springframework/boot/context/config/ConfigDataEnvironmentUpdateListener.java

@@ -0,0 +1,56 @@
+/*
+ * 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.context.config;
+
+import java.util.EventListener;
+
+import org.springframework.core.env.Environment;
+import org.springframework.core.env.PropertySource;
+
+/**
+ * {@link EventListener} to listen to {@link Environment} updates triggered by the
+ * {@link ConfigDataEnvironmentPostProcessor}.
+ *
+ * @author Phillip Webb
+ * @since 2.4.2
+ */
+public interface ConfigDataEnvironmentUpdateListener extends EventListener {
+
+	/**
+	 * A {@link ConfigDataEnvironmentUpdateListener} that does nothing.
+	 */
+	ConfigDataEnvironmentUpdateListener NONE = new ConfigDataEnvironmentUpdateListener() {
+	};
+
+	/**
+	 * Called when a new {@link PropertySource} is added to the {@link Environment}.
+	 * @param propertySource the {@link PropertySource} that was added
+	 * @param location the original {@link ConfigDataLocation} of the source.
+	 * @param resource the {@link ConfigDataResource} of the source.
+	 */
+	default void onPropertySourceAdded(PropertySource<?> propertySource, ConfigDataLocation location,
+			ConfigDataResource resource) {
+	}
+
+	/**
+	 * Called when {@link Environment} profiles are set.
+	 * @param profiles the profiles being set
+	 */
+	default void onSetProfiles(Profiles profiles) {
+	}
+
+}

spring-boot-project/spring-boot/src/test/java/org/springframework/boot/context/config/ConfigDataEnvironmentPostProcessorTests.java

@@ -16,6 +16,7 @@
 
 package org.springframework.boot.context.config;
 
+import java.util.Collections;
 import java.util.Set;
 import java.util.function.Supplier;
 
@@ -119,9 +120,13 @@ void postProcessEnvironmentWhenUseLegacyProcessingSwitchesToLegacyMethod() {
 	@Test
 	void applyToAppliesPostProcessing() {
 		int before = this.environment.getPropertySources().size();
-		ConfigDataEnvironmentPostProcessor.applyTo(this.environment, null, null, "dev");
+		TestConfigDataEnvironmentUpdateListener listener = new TestConfigDataEnvironmentUpdateListener();
+		ConfigDataEnvironmentPostProcessor.applyTo(this.environment, null, null, Collections.singleton("dev"),
+				listener);
 		assertThat(this.environment.getPropertySources().size()).isGreaterThan(before);
 		assertThat(this.environment.getActiveProfiles()).containsExactly("dev");
+		assertThat(listener.getAddedPropertySources()).hasSizeGreaterThan(0);
+		assertThat(listener.getProfiles().getActive()).containsExactly("dev");
 	}
 
 }