GH-1487 - Fall back to Spring-based task executor for ApplicationModulesBootstrap.

We are now using SimpleAsyncTaskExecutor as a fallback in case ApplicationModulesBootstrap is invoked without an Executor instance in the first place. That makes sure that the ClassLoader is properly propagated to the new Thread created and user classes are fully loadable.

Author: odrotbohm

spring-modulith-runtime/src/main/java/org/springframework/modulith/runtime/autoconfigure/SpringModulithRuntimeAutoConfiguration.java

@@ -42,13 +42,15 @@
 import org.springframework.boot.context.event.ApplicationStartedEvent;
 import org.springframework.boot.context.properties.EnableConfigurationProperties;
 import org.springframework.boot.flyway.autoconfigure.FlywayMigrationStrategy;
+import org.springframework.boot.system.JavaVersion;
 import org.springframework.context.ApplicationContext;
 import org.springframework.context.ApplicationListener;
 import org.springframework.context.annotation.Bean;
 import org.springframework.context.annotation.Lazy;
 import org.springframework.context.annotation.Role;
 import org.springframework.core.io.Resource;
 import org.springframework.core.io.support.SpringFactoriesLoader;
+import org.springframework.core.task.SimpleAsyncTaskExecutor;
 import org.springframework.modulith.ApplicationModuleInitializer;
 import org.springframework.modulith.core.ApplicationModule;
 import org.springframework.modulith.core.ApplicationModuleIdentifier;
@@ -200,14 +202,35 @@ static class ApplicationModulesBootstrap {
 			Supplier<ApplicationModules> supplier = () -> initializeApplicationModules(applicationMainClass);
 
 			this.modules = executor == null
-					? CompletableFuture.supplyAsync(supplier)
+					? withFallbackExecutor(supplier)
 					: CompletableFuture.supplyAsync(supplier, executor);
+
 		}
 
 		CompletableFuture<ApplicationModules> getApplicationModules() {
 			return modules;
 		}
 
+		/**
+		 * We didn't get an {@link Executor} instance handed in, so asynchronously execute the supplier through a Spring
+		 * {@link SimpleAsyncTaskExecutor} to make sure we see the right {@link ClassLoader} during the execution.
+		 *
+		 * @param <T>
+		 * @param supplier
+		 * @return
+		 */
+		private static <T> CompletableFuture<T> withFallbackExecutor(Supplier<T> supplier) {
+
+			var fallback = new SimpleAsyncTaskExecutor();
+
+			if (JavaVersion.getJavaVersion().isEqualOrNewerThan(JavaVersion.TWENTY_ONE)) {
+				fallback.setVirtualThreads(true);
+			}
+
+			return fallback.submitCompletable(supplier::get)
+					.whenComplete((m, t) -> fallback.close());
+		}
+
 		static ApplicationModules initializeApplicationModules(Class<?> applicationMainClass) {
 
 			LOGGER.debug("Obtaining Spring Modulith application modules…");