Introduce DynamicPropertyRegistrar support

This is a PROOF OF CONCEPT which introduces DynamicPropertyRegistrar
support as a replacement for registering a DynamicPropertyRegistry as
a bean in the ApplicationContext.

It appears that most things work as expected; however, in this POC there
are two instances of DefaultDynamicPropertyRegistry that prevent the use
of @⁠DynamicPropertySource and DynamicPropertyRegistrar in the same
ApplicationContext, since the two features end up writing to two different
valueSuppliers maps. The commented-out "magic.word" assertions in
DynamicPropertySourceIntegrationTests therefore currently fail.

See spring-projectsgh-33501

spring-test/src/main/java/org/springframework/test/context/DynamicPropertyRegistrar.java

@@ -0,0 +1,33 @@
+/*
+ * Copyright 2002-2024 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.test.context;
+
+/**
+ * Registrar that is used to add properties with dynamically resolved values to
+ * the {@code Environment} via a {@link DynamicPropertyRegistry}.
+ *
+ * @author Sam Brannen
+ * @since 6.2
+ * @see DynamicPropertySource
+ * @see DynamicPropertyRegistry
+ */
+@FunctionalInterface
+public interface DynamicPropertyRegistrar {
+
+	void accept(DynamicPropertyRegistry registry);
+
+}

spring-test/src/main/java/org/springframework/test/context/support/DynamicPropertiesContextCustomizer.java

@@ -46,15 +46,12 @@
  * @since 5.2.5
  * @see DynamicPropertiesContextCustomizerFactory
  * @see DefaultDynamicPropertyRegistry
- * @see DynamicPropertySourceBeanInitializer
+ * @see DynamicPropertyRegistrarBeanInitializer
  */
 class DynamicPropertiesContextCustomizer implements ContextCustomizer {
 
-	private static final String DYNAMIC_PROPERTY_REGISTRY_BEAN_NAME =
-			DynamicPropertiesContextCustomizer.class.getName() + ".dynamicPropertyRegistry";
-
-	private static final String DYNAMIC_PROPERTY_SOURCE_BEAN_INITIALIZER_BEAN_NAME =
-			DynamicPropertiesContextCustomizer.class.getName() + ".dynamicPropertySourceBeanInitializer";
+	private static final String DYNAMIC_PROPERTY_REGISTRAR_BEAN_INITIALIZER_BEAN_NAME =
+			DynamicPropertiesContextCustomizer.class.getName() + ".dynamicPropertyRegistrarBeanInitializer";
 
 
 	private final Set<Method> methods;
@@ -68,24 +65,22 @@ class DynamicPropertiesContextCustomizer implements ContextCustomizer {
 
 	@Override
 	public void customizeContext(ConfigurableApplicationContext context, MergedContextConfiguration mergedConfig) {
-		ConfigurableEnvironment environment = context.getEnvironment();
 		ConfigurableListableBeanFactory beanFactory = context.getBeanFactory();
 		if (!(beanFactory instanceof BeanDefinitionRegistry beanDefinitionRegistry)) {
 			throw new IllegalStateException("BeanFactory must be a BeanDefinitionRegistry");
 		}
 
-		DefaultDynamicPropertyRegistry dynamicPropertyRegistry =
-				new DefaultDynamicPropertyRegistry(environment, this.methods.isEmpty());
-		beanFactory.registerSingleton(DYNAMIC_PROPERTY_REGISTRY_BEAN_NAME, dynamicPropertyRegistry);
-
-		if (!beanDefinitionRegistry.containsBeanDefinition(DYNAMIC_PROPERTY_SOURCE_BEAN_INITIALIZER_BEAN_NAME)) {
-			BeanDefinition beanDefinition = new RootBeanDefinition(DynamicPropertySourceBeanInitializer.class);
+		if (!beanDefinitionRegistry.containsBeanDefinition(DYNAMIC_PROPERTY_REGISTRAR_BEAN_INITIALIZER_BEAN_NAME)) {
+			BeanDefinition beanDefinition = new RootBeanDefinition(DynamicPropertyRegistrarBeanInitializer.class);
 			beanDefinition.setRole(BeanDefinition.ROLE_INFRASTRUCTURE);
 			beanDefinitionRegistry.registerBeanDefinition(
-					DYNAMIC_PROPERTY_SOURCE_BEAN_INITIALIZER_BEAN_NAME, beanDefinition);
+					DYNAMIC_PROPERTY_REGISTRAR_BEAN_INITIALIZER_BEAN_NAME, beanDefinition);
 		}
 
 		if (!this.methods.isEmpty()) {
+			ConfigurableEnvironment environment = context.getEnvironment();
+			DefaultDynamicPropertyRegistry dynamicPropertyRegistry =
+					new DefaultDynamicPropertyRegistry(environment, false);
 			MutablePropertySources propertySources = environment.getPropertySources();
 			propertySources.addFirst(new DynamicValuesPropertySource(dynamicPropertyRegistry.valueSuppliers));
 			this.methods.forEach(method -> {

spring-test/src/main/java/org/springframework/test/context/support/DynamicPropertyRegistrarBeanInitializer.java

@@ -0,0 +1,76 @@
+/*
+ * Copyright 2002-2024 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.test.context.support;
+
+import org.apache.commons.logging.Log;
+import org.apache.commons.logging.LogFactory;
+
+import org.springframework.beans.factory.BeanFactoryInitializer;
+import org.springframework.beans.factory.BeanFactoryUtils;
+import org.springframework.beans.factory.ListableBeanFactory;
+import org.springframework.context.EnvironmentAware;
+import org.springframework.core.env.ConfigurableEnvironment;
+import org.springframework.core.env.Environment;
+import org.springframework.lang.Nullable;
+import org.springframework.test.context.DynamicPropertyRegistrar;
+
+/**
+ * Internal component which eagerly initializes {@link DynamicPropertyRegistrar}
+ * beans.
+ *
+ * @author Sam Brannen
+ * @since 6.2
+ */
+class DynamicPropertyRegistrarBeanInitializer implements BeanFactoryInitializer<ListableBeanFactory>, EnvironmentAware {
+
+	private static final Log logger = LogFactory.getLog(DynamicPropertyRegistrarBeanInitializer.class);
+
+
+	@Nullable
+	private ConfigurableEnvironment environment;
+
+
+	@Override
+	public void setEnvironment(Environment environment) {
+		if (!(environment instanceof ConfigurableEnvironment configurableEnvironment)) {
+			throw new IllegalArgumentException("Environment must be a ConfigurableEnvironment");
+		}
+		this.environment = configurableEnvironment;
+	}
+
+	@Override
+	public void initialize(ListableBeanFactory beanFactory) {
+		if (this.environment == null) {
+			throw new IllegalStateException("Environment is required");
+		}
+		String[] beanNames = BeanFactoryUtils.beanNamesForTypeIncludingAncestors(
+				beanFactory, DynamicPropertyRegistrar.class);
+		if (beanNames.length > 0) {
+			DefaultDynamicPropertyRegistry dynamicPropertyRegistry =
+					new DefaultDynamicPropertyRegistry(this.environment, true);
+
+			for (String name : beanNames) {
+				if (logger.isDebugEnabled()) {
+					logger.debug("Eagerly initializing DynamicPropertyRegistrar bean '%s'".formatted(name));
+				}
+				DynamicPropertyRegistrar registrar = beanFactory.getBean(name, DynamicPropertyRegistrar.class);
+				registrar.accept(dynamicPropertyRegistry);
+			}
+		}
+	}
+
+}

spring-test/src/test/java/org/springframework/test/context/DynamicPropertiesTestSuite.java

@@ -41,7 +41,7 @@
 @Suite
 @SelectClasses(
 	value = {
-		DynamicPropertyRegistryIntegrationTests.class,
+		DynamicPropertyRegistrarIntegrationTests.class,
 		DynamicPropertySourceIntegrationTests.class
 	},
 	names = {

spring-test/src/test/java/org/springframework/test/context/DynamicPropertyRegistryIntegrationTests.java → spring-test/src/test/java/org/springframework/test/context/DynamicPropertyRegistrarIntegrationTests.java

@@ -29,20 +29,29 @@
 import org.springframework.test.context.junit.jupiter.SpringJUnitConfig;
 
 import static org.assertj.core.api.Assertions.assertThat;
+import static org.assertj.core.api.Assertions.assertThatRuntimeException;
 
 /**
- * Integration tests for {@link DynamicPropertyRegistry} bean support.
+ * Integration tests for {@link DynamicPropertyRegistrar} bean support.
  *
  * @author Sam Brannen
  * @since 6.2
  * @see DynamicPropertySourceIntegrationTests
  */
 @SpringJUnitConfig
 @TestPropertySource(properties = "api.url: https://example.com/test")
-class DynamicPropertyRegistryIntegrationTests {
+class DynamicPropertyRegistrarIntegrationTests {
 
 	private static final String API_URL = "api.url";
 
+	@Test
+	void customDynamicPropertyRegistryCanExistInApplicationContext(
+			@Autowired DynamicPropertyRegistry dynamicPropertyRegistry) {
+
+		assertThatRuntimeException()
+				.isThrownBy(() -> dynamicPropertyRegistry.add("test", () -> "test"))
+				.withMessage("Boom!");
+	}
 
 	@Test
 	void dynamicPropertySourceOverridesTestPropertySource(@Autowired ConfigurableEnvironment env) {
@@ -90,16 +99,25 @@ private static void assertApiUrlIsDynamic(String apiUrl) {
 	@Import({ EnvironmentInjectedService.class, ConstructorInjectedService.class, SetterInjectedService.class })
 	static class Config {
 
-		// Annotating this @Bean method with @DynamicPropertySource ensures that
-		// this bean will be instantiated before any other singleton beans in the
+		@Bean
+		ApiServer apiServer() {
+			return new ApiServer();
+		}
+
+		// Accepting ApiServer as a method argument ensures that the apiServer
+		// bean will be instantiated before any other singleton beans in the
 		// context which further ensures that the dynamic "api.url" property is
 		// available to all standard singleton beans.
 		@Bean
-		@DynamicPropertySource
-		ApiServer apiServer(DynamicPropertyRegistry registry) {
-			ApiServer apiServer = new ApiServer();
-			registry.add(API_URL, apiServer::getUrl);
-			return apiServer;
+		DynamicPropertyRegistrar apiServerProperties(ApiServer apiServer) {
+			return registry -> registry.add(API_URL, apiServer::getUrl);
+		}
+
+		@Bean
+		DynamicPropertyRegistry dynamicPropertyRegistry() {
+			return (name, valueSupplier) -> {
+				throw new RuntimeException("Boom!");
+			};
 		}
 
 	}

spring-test/src/test/java/org/springframework/test/context/DynamicPropertySourceIntegrationTests.java

@@ -23,21 +23,24 @@
 
 import org.springframework.beans.factory.annotation.Autowired;
 import org.springframework.beans.factory.annotation.Value;
+import org.springframework.context.annotation.Bean;
 import org.springframework.context.annotation.Configuration;
 import org.springframework.context.annotation.Import;
 import org.springframework.core.env.ConfigurableEnvironment;
 import org.springframework.core.env.MutablePropertySources;
 import org.springframework.test.context.junit.jupiter.SpringJUnitConfig;
 
 import static org.assertj.core.api.Assertions.assertThat;
+import static org.assertj.core.api.Assertions.assertThatRuntimeException;
 import static org.junit.jupiter.api.TestInstance.Lifecycle.PER_CLASS;
 
 /**
- * Integration tests for {@link DynamicPropertySource @DynamicPropertySource}.
+ * Integration tests for {@link DynamicPropertySource @DynamicPropertySource} and
+ * {@link DynamicPropertyRegistrar} bean support.
  *
  * @author Phillip Webb
  * @author Sam Brannen
- * @see DynamicPropertyRegistryIntegrationTests
+ * @see DynamicPropertyRegistrarIntegrationTests
  */
 @SpringJUnitConfig
 @TestPropertySource(properties = "test.container.ip: test")
@@ -54,8 +57,12 @@ class DynamicPropertySourceIntegrationTests {
 	static final DemoContainer container = new DemoContainer();
 
 	@DynamicPropertySource
-	static void containerProperties(DynamicPropertyRegistry registry) {
+	static void containerPropertiesIpAddress(DynamicPropertyRegistry registry) {
 		registry.add(TEST_CONTAINER_IP, container::getIpAddress);
+	}
+
+	@DynamicPropertySource
+	static void containerPropertiesPort(DynamicPropertyRegistry registry) {
 		registry.add("test.container.port", container::getPort);
 	}
 
@@ -65,6 +72,16 @@ void clearSystemProperty() {
 		System.clearProperty(TEST_CONTAINER_IP);
 	}
 
+	@Test
+	@DisplayName("A custom DynamicPropertyRegistry bean can exist in the ApplicationContext")
+	void customDynamicPropertyRegistryCanExistInApplicationContext(
+			@Autowired DynamicPropertyRegistry dynamicPropertyRegistry) {
+
+		assertThatRuntimeException()
+				.isThrownBy(() -> dynamicPropertyRegistry.add("test", () -> "test"))
+				.withMessage("Boom!");
+	}
+
 	@Test
 	@DisplayName("@DynamicPropertySource overrides @TestPropertySource and JVM system property")
 	void dynamicPropertySourceOverridesTestPropertySourceAndSystemProperty(@Autowired ConfigurableEnvironment env) {
@@ -74,9 +91,11 @@ void dynamicPropertySourceOverridesTestPropertySourceAndSystemProperty(@Autowire
 		assertThat(propertySources.contains("Inlined Test Properties")).isTrue();
 		assertThat(propertySources.contains("systemProperties")).isTrue();
 		assertThat(propertySources.get("Dynamic Test Properties").getProperty(TEST_CONTAINER_IP)).isEqualTo("127.0.0.1");
+		// assertThat(propertySources.get("Dynamic Test Properties").getProperty("magic.word")).isEqualTo("enigma");
 		assertThat(propertySources.get("Inlined Test Properties").getProperty(TEST_CONTAINER_IP)).isEqualTo("test");
 		assertThat(propertySources.get("systemProperties").getProperty(TEST_CONTAINER_IP)).isEqualTo("system");
 		assertThat(env.getProperty(TEST_CONTAINER_IP)).isEqualTo("127.0.0.1");
+		// assertThat(env.getProperty("magic.word")).isEqualTo("enigma");
 	}
 
 	@Test
@@ -90,6 +109,19 @@ void serviceHasInjectedValues(@Autowired Service service) {
 	@Configuration
 	@Import(Service.class)
 	static class Config {
+
+		@Bean
+		DynamicPropertyRegistrar magicWordProperties() {
+			return registry -> registry.add("magic.word", () -> "engima");
+		}
+
+		@Bean
+		DynamicPropertyRegistry dynamicPropertyRegistry() {
+			return (name, valueSupplier) -> {
+				throw new RuntimeException("Boom!");
+			};
+		}
+
 	}
 
 	static class Service {