Don't use RestartClassLoader when proxying classes it did not load

Fixes gh-19010
Fixes gh-25367

spring-boot-project/spring-boot-devtools/build.gradle

@@ -70,6 +70,7 @@ dependencies {
 	testImplementation("org.thymeleaf:thymeleaf-spring5")
 	testImplementation("nz.net.ultraq.thymeleaf:thymeleaf-layout-dialect")
 
+	testRuntimeOnly("org.aspectj:aspectjweaver")
 	testRuntimeOnly("org.yaml:snakeyaml")
 }
 

spring-boot-project/spring-boot-devtools/src/main/java/org/springframework/boot/devtools/restart/classloader/RestartClassLoader.java

@@ -173,6 +173,11 @@ public class RestartClassLoader extends URLClassLoader implements SmartClassLoad
 		return defineClass(name, b, 0, b.length, protectionDomain);
 	}
 
+	@Override
+	public ClassLoader getOriginalClassLoader() {
+		return getParent();
+	}
+
 	private URL createFileUrl(String name, ClassLoaderFile file) {
 		try {
 			return new URL("reloaded", null, -1, "/" + name, new ClassLoaderFileURLStreamHandler(file));

spring-boot-project/spring-boot-devtools/src/test/java/org/springframework/boot/devtools/restart/classloader/RestartClassLoaderTests.java

@@ -20,6 +20,7 @@ import java.io.File;
 import java.io.FileOutputStream;
 import java.io.IOException;
 import java.io.InputStream;
+import java.net.MalformedURLException;
 import java.net.URL;
 import java.net.URLClassLoader;
 import java.nio.charset.StandardCharsets;
@@ -36,7 +37,14 @@ import org.junit.jupiter.api.Test;
 import org.junit.jupiter.api.io.TempDir;
 
 import org.springframework.aop.framework.ProxyFactory;
+import org.springframework.aop.support.AopUtils;
 import org.springframework.boot.devtools.restart.classloader.ClassLoaderFile.Kind;
+import org.springframework.boot.test.context.runner.ApplicationContextRunner;
+import org.springframework.context.annotation.Bean;
+import org.springframework.context.annotation.Configuration;
+import org.springframework.context.annotation.EnableAspectJAutoProxy;
+import org.springframework.transaction.annotation.EnableTransactionManagement;
+import org.springframework.transaction.annotation.Transactional;
 import org.springframework.util.FileCopyUtils;
 import org.springframework.util.StreamUtils;
 
@@ -210,6 +218,20 @@ class RestartClassLoaderTests {
 		// Warning would happen outside the boundary of the test
 	}
 
+	@Test
+	void packagePrivateClassLoadedByParentClassLoaderCanBeProxied() throws MalformedURLException {
+		new ApplicationContextRunner()
+				.withClassLoader(new RestartClassLoader(ExampleTransactional.class.getClassLoader(),
+						new URL[] { this.sampleJarFile.toURI().toURL() }, this.updatedFiles))
+				.withUserConfiguration(ProxyConfiguration.class).run((context) -> {
+					assertThat(context).hasNotFailed();
+					ExampleTransactional transactional = context.getBean(ExampleTransactional.class);
+					assertThat(AopUtils.isCglibProxy(transactional)).isTrue();
+					assertThat(transactional.getClass().getClassLoader())
+							.isEqualTo(ExampleTransactional.class.getClassLoader());
+				});
+	}
+
 	private String readString(InputStream in) throws IOException {
 		return new String(FileCopyUtils.copyToByteArray(in));
 	}
@@ -218,4 +240,32 @@ class RestartClassLoaderTests {
 		return (enumeration != null) ? Collections.list(enumeration) : Collections.emptyList();
 	}
 
+	@Configuration(proxyBeanMethods = false)
+	@EnableAspectJAutoProxy(proxyTargetClass = true)
+	@EnableTransactionManagement
+	static class ProxyConfiguration {
+
+		@Bean
+		ExampleTransactional exampleTransactional() {
+			return new ExampleTransactional();
+		}
+
+	}
+
+	static class ExampleTransactional implements ExampleInterface {
+
+		@Override
+		@Transactional
+		public String doIt() {
+			return "hello";
+		}
+
+	}
+
+	interface ExampleInterface {
+
+		String doIt();
+
+	}
+
 }