Lazily resolve JPA fallback bootstrap executor

Previously, the `entityManagerFactoryBuilder` bean method injected a
`Map<String, AsyncTaskExecutor>` to determine the fallback executor used
for background JPA bootstrapping. A `Map` parameter is resolved eagerly,
so this forced early initialization of every `AsyncTaskExecutor` bean
whenever the builder was created, even when background bootstrapping was
not in use. When an `AsyncTaskExecutor` directly or transitively
depended on the `EntityManagerFactory`, this resulted in a
`BeanCurrentlyInCreationException`.

The fallback executor is now resolved lazily.
`EntityManagerFactoryBuilder` holds a `Supplier` that is only invoked
when background bootstrapping is actually required, and the executor is
then looked up from the `BeanFactory` rather than eagerly injected. A
new `Supplier`-based constructor is added for this purpose; the existing
constructor that accepts an `AsyncTaskExecutor` is retained and
delegates to it.

The same eager `Map<String, AsyncTaskExecutor>` injection, along with an
unused private method, is also removed from
`DataJpaRepositoriesAutoConfiguration`.

See gh-50801

Signed-off-by: Ns <397827222@qq.com>

module/spring-boot-data-jpa/src/main/java/org/springframework/boot/data/jpa/autoconfigure/DataJpaRepositoriesAutoConfiguration.java

@@ -16,12 +16,8 @@
 
 package org.springframework.boot.data.jpa.autoconfigure;
 
-import java.util.Map;
-
 import javax.sql.DataSource;
 
-import org.jspecify.annotations.Nullable;
-
 import org.springframework.boot.LazyInitializationExcludeFilter;
 import org.springframework.boot.autoconfigure.AutoConfiguration;
 import org.springframework.boot.autoconfigure.EnableAutoConfiguration;
@@ -38,7 +34,6 @@ import org.springframework.boot.jpa.autoconfigure.EntityManagerFactoryBuilderCus
 import org.springframework.context.annotation.Bean;
 import org.springframework.context.annotation.Import;
 import org.springframework.context.annotation.ImportSelector;
-import org.springframework.core.task.AsyncTaskExecutor;
 import org.springframework.core.type.AnnotationMetadata;
 import org.springframework.data.envers.repository.config.EnableEnversRepositories;
 import org.springframework.data.envers.repository.support.EnversRevisionRepositoryFactoryBean;
@@ -83,8 +78,7 @@ public final class DataJpaRepositoriesAutoConfiguration {
 
 	@Bean
 	@ConditionalOnProperty(name = "spring.data.jpa.repositories.bootstrap-mode", havingValue = "deferred")
-	EntityManagerFactoryBuilderCustomizer entityManagerFactoryBootstrapExecutorCustomizer(
-			Map<String, AsyncTaskExecutor> taskExecutors) {
+	EntityManagerFactoryBuilderCustomizer entityManagerFactoryBootstrapExecutorCustomizer() {
 		return (builder) -> builder.requireBootstrapExecutor(() -> BootstrapExecutorRequiredException
 			.ofProperty("spring.data.jpa.repositories.bootstrap-mode", "deferred"));
 	}
@@ -94,13 +88,6 @@ public final class DataJpaRepositoriesAutoConfiguration {
 		return (name, definition, type) -> "org.springframework.data.jpa.util.JpaMetamodelCacheCleanup".equals(name);
 	}
 
-	private @Nullable AsyncTaskExecutor determineBootstrapExecutor(Map<String, AsyncTaskExecutor> taskExecutors) {
-		if (taskExecutors.size() == 1) {
-			return taskExecutors.values().iterator().next();
-		}
-		return taskExecutors.get(TaskExecutionAutoConfiguration.APPLICATION_TASK_EXECUTOR_BEAN_NAME);
-	}
-
 	static class JpaRepositoriesImportSelector implements ImportSelector {
 
 		private static final boolean ENVERS_AVAILABLE = ClassUtils.isPresent(

module/spring-boot-hibernate/src/test/java/org/springframework/boot/hibernate/autoconfigure/HibernateJpaAutoConfigurationTests.java

@@ -303,6 +303,15 @@ class HibernateJpaAutoConfigurationTests {
 		return (builder) -> builder.setBootstrapExecutor(new SimpleAsyncTaskExecutor());
 	}
 
+	@Test
+	void whenAsyncTaskExecutorIsDefinedInJpaDependentConfigurationDoesNotTriggerABeanCurrentlyInCreationException() {
+		this.contextRunner.withUserConfiguration(AsyncTaskExecutorDependingOnEntityManagerFactoryConfiguration.class)
+			.run((context) -> {
+				assertThat(context).hasNotFailed();
+				assertThat(context).hasSingleBean(EntityManagerFactory.class);
+			});
+	}
+
 	@Test
 	void customJpaProperties() {
 		this.contextRunner
@@ -1474,4 +1483,17 @@ class HibernateJpaAutoConfigurationTests {
 
 	}
 
+	@Configuration(proxyBeanMethods = false)
+	static class AsyncTaskExecutorDependingOnEntityManagerFactoryConfiguration {
+
+		AsyncTaskExecutorDependingOnEntityManagerFactoryConfiguration(EntityManagerFactory entityManagerFactory) {
+		}
+
+		@Bean
+		SimpleAsyncTaskExecutor exampleTaskExecutor() {
+			return new SimpleAsyncTaskExecutor();
+		}
+
+	}
+
 }

module/spring-boot-jpa/src/main/java/org/springframework/boot/jpa/EntityManagerFactoryBuilder.java

@@ -68,7 +68,7 @@ public class EntityManagerFactoryBuilder {
 
 	private final @Nullable URL persistenceUnitRootLocation;
 
-	private final @Nullable AsyncTaskExecutor fallbackBootstrapExecutor;
+	private final Supplier<? extends @Nullable AsyncTaskExecutor> fallbackBootstrapExecutor;
 
 	private @Nullable AsyncTaskExecutor bootstrapExecutor;
 
@@ -105,7 +105,7 @@ public class EntityManagerFactoryBuilder {
 	public EntityManagerFactoryBuilder(JpaVendorAdapter jpaVendorAdapter,
 			Function<DataSource, Map<String, ?>> jpaPropertiesFactory,
 			@Nullable PersistenceUnitManager persistenceUnitManager, @Nullable URL persistenceUnitRootLocation) {
-		this(jpaVendorAdapter, jpaPropertiesFactory, persistenceUnitManager, persistenceUnitRootLocation, null);
+		this(jpaVendorAdapter, jpaPropertiesFactory, persistenceUnitManager, persistenceUnitRootLocation, () -> null);
 	}
 
 	/**
@@ -126,6 +126,29 @@ public class EntityManagerFactoryBuilder {
 			Function<DataSource, Map<String, ?>> jpaPropertiesFactory,
 			@Nullable PersistenceUnitManager persistenceUnitManager, @Nullable URL persistenceUnitRootLocation,
 			@Nullable AsyncTaskExecutor fallbackBootstrapExecutor) {
+		this(jpaVendorAdapter, jpaPropertiesFactory, persistenceUnitManager, persistenceUnitRootLocation,
+				() -> fallbackBootstrapExecutor);
+	}
+
+	/**
+	 * Create a new instance passing in the common pieces that will be shared if multiple
+	 * EntityManagerFactory instances are created.
+	 * @param jpaVendorAdapter a vendor adapter
+	 * @param jpaPropertiesFactory the JPA properties to be passed to the persistence
+	 * provider, based on the {@linkplain #dataSource(DataSource) configured data source}
+	 * @param persistenceUnitManager optional source of persistence unit information (can
+	 * be null)
+	 * @param persistenceUnitRootLocation the persistence unit root location to use as a
+	 * fallback or {@code null}
+	 * @param fallbackBootstrapExecutor a supplier of the fallback executor to use when
+	 * background bootstrapping is required but no explicit executor has been set. The
+	 * supplier is only invoked when background bootstrapping is actually required.
+	 * @since 4.1.1
+	 */
+	public EntityManagerFactoryBuilder(JpaVendorAdapter jpaVendorAdapter,
+			Function<DataSource, Map<String, ?>> jpaPropertiesFactory,
+			@Nullable PersistenceUnitManager persistenceUnitManager, @Nullable URL persistenceUnitRootLocation,
+			Supplier<? extends @Nullable AsyncTaskExecutor> fallbackBootstrapExecutor) {
 		this.jpaVendorAdapter = jpaVendorAdapter;
 		this.persistenceUnitManager = persistenceUnitManager;
 		this.jpaPropertiesFactory = jpaPropertiesFactory;
@@ -343,8 +366,9 @@ public class EntityManagerFactoryBuilder {
 				return EntityManagerFactoryBuilder.this.bootstrapExecutor;
 			}
 			if (EntityManagerFactoryBuilder.this.requireBootstrapExecutorExceptionSupplier != null) {
-				if (EntityManagerFactoryBuilder.this.fallbackBootstrapExecutor != null) {
-					return EntityManagerFactoryBuilder.this.fallbackBootstrapExecutor;
+				@Nullable AsyncTaskExecutor fallback = EntityManagerFactoryBuilder.this.fallbackBootstrapExecutor.get();
+				if (fallback != null) {
+					return fallback;
 				}
 				RuntimeException ex = EntityManagerFactoryBuilder.this.requireBootstrapExecutorExceptionSupplier.get();
 				throw (ex != null) ? ex : new IllegalStateException("A bootstrap executor is required");

module/spring-boot-jpa/src/main/java/org/springframework/boot/jpa/autoconfigure/JpaBaseConfiguration.java

@@ -28,6 +28,7 @@ import org.apache.commons.logging.LogFactory;
 import org.jspecify.annotations.Nullable;
 
 import org.springframework.beans.factory.BeanFactory;
+import org.springframework.beans.factory.ListableBeanFactory;
 import org.springframework.beans.factory.ObjectProvider;
 import org.springframework.boot.autoconfigure.AutoConfigurationPackages;
 import org.springframework.boot.autoconfigure.EnableAutoConfiguration;
@@ -123,11 +124,10 @@ public abstract class JpaBaseConfiguration {
 	@ConditionalOnMissingBean
 	public EntityManagerFactoryBuilder entityManagerFactoryBuilder(JpaVendorAdapter jpaVendorAdapter,
 			ObjectProvider<PersistenceUnitManager> persistenceUnitManager,
-			ObjectProvider<EntityManagerFactoryBuilderCustomizer> customizers,
-			Map<String, AsyncTaskExecutor> taskExecutors) {
-		AsyncTaskExecutor bootstrapExecutor = determineBootstrapExecutor(taskExecutors);
+			ObjectProvider<EntityManagerFactoryBuilderCustomizer> customizers, ListableBeanFactory beanFactory) {
 		EntityManagerFactoryBuilder builder = new EntityManagerFactoryBuilder(jpaVendorAdapter,
-				this::buildJpaProperties, persistenceUnitManager.getIfAvailable(), null, bootstrapExecutor);
+				this::buildJpaProperties, persistenceUnitManager.getIfAvailable(), null,
+				() -> determineBootstrapExecutor(beanFactory));
 		if (this.properties.getBootstrap() == Bootstrap.ASYNC) {
 			builder.requireBootstrapExecutor(
 					() -> BootstrapExecutorRequiredException.ofProperty("spring.jpa.bootstrap", "async"));
@@ -136,7 +136,8 @@ public abstract class JpaBaseConfiguration {
 		return builder;
 	}
 
-	private @Nullable AsyncTaskExecutor determineBootstrapExecutor(Map<String, AsyncTaskExecutor> taskExecutors) {
+	private @Nullable AsyncTaskExecutor determineBootstrapExecutor(ListableBeanFactory beanFactory) {
+		Map<String, AsyncTaskExecutor> taskExecutors = beanFactory.getBeansOfType(AsyncTaskExecutor.class);
 		return (taskExecutors.size() == 1) ? taskExecutors.values().iterator().next()
 				: taskExecutors.get(TaskExecutionAutoConfiguration.APPLICATION_TASK_EXECUTOR_BEAN_NAME);
 	}

module/spring-boot-jpa/src/test/java/org/springframework/boot/jpa/EntityManagerFactoryBuilderTests.java

@@ -18,7 +18,9 @@ package org.springframework.boot.jpa;
 
 import java.util.Collections;
 import java.util.Map;
+import java.util.concurrent.atomic.AtomicBoolean;
 import java.util.function.Function;
+import java.util.function.Supplier;
 
 import javax.sql.DataSource;
 
@@ -125,6 +127,26 @@ class EntityManagerFactoryBuilderTests {
 			.withMessage("A bootstrap executor is required");
 	}
 
+	@Test
+	void requireBootstrapExecutorWhenFallbackExecutorSupplierProvidesExecutorDoesNotThrow() {
+		EntityManagerFactoryBuilder builder = createEmptyBuilderWithFallbackSupplier(SimpleAsyncTaskExecutor::new);
+		builder.requireBootstrapExecutor(() -> new IllegalStateException("BAD"));
+		DataSource dataSource = mock();
+		assertThatNoException().isThrownBy(builder.dataSource(dataSource)::build);
+	}
+
+	@Test
+	void fallbackExecutorSupplierIsNotInvokedWhenBootstrapExecutorNotRequired() {
+		AtomicBoolean invoked = new AtomicBoolean();
+		EntityManagerFactoryBuilder builder = createEmptyBuilderWithFallbackSupplier(() -> {
+			invoked.set(true);
+			return new SimpleAsyncTaskExecutor();
+		});
+		DataSource dataSource = mock();
+		builder.dataSource(dataSource).build();
+		assertThat(invoked).isFalse();
+	}
+
 	private EntityManagerFactoryBuilder createEmptyBuilder() {
 		return createEmptyBuilder(null);
 	}
@@ -135,6 +157,13 @@ class EntityManagerFactoryBuilderTests {
 				fallbackBootstrapExecutor);
 	}
 
+	private EntityManagerFactoryBuilder createEmptyBuilderWithFallbackSupplier(
+			Supplier<? extends @Nullable AsyncTaskExecutor> fallbackBootstrapExecutorSupplier) {
+		Function<DataSource, Map<String, ?>> jpaPropertiesFactory = (dataSource) -> Collections.emptyMap();
+		return new EntityManagerFactoryBuilder(new TestJpaVendorAdapter(), jpaPropertiesFactory, null, null,
+				fallbackBootstrapExecutorSupplier);
+	}
+
 	static class TestJpaVendorAdapter extends AbstractJpaVendorAdapter {
 
 		@Override