ClassCastException: XXX$$SpringCGLIB$$0 cannot be cast to org.springframework.cglib.proxy.Factory with custom ClassLoader

[AlexanderShchelkunov]

demo.zip

Description

Hello!

I have a Spring Boot application, that supports 3rd party plugins. Because of that I need to use a custom class loader. But if there is a @Configuration that has @Lazy annotation (when Spring has to create a proxy), the app will not start. See the possible way to fix at the bottom.

Environment

Spring Boot: 3.3.3
Spring Framework: 6.1.12
Java: JDK 17

Steps to Reproduce

Start the app

Error Message

Caused by: java.lang.ClassCastException: class com.example.demo.SomeConfig$$SpringCGLIB$$0 cannot be cast to class org.springframework.cglib.proxy.Factory (com.example.demo.SomeConfig$$SpringCGLIB$$0 and org.springframework.cglib.proxy.Factory are in unnamed module of loader org.springframework.boot.loader.launch.LaunchedClassLoader @433c675d)
        at org.springframework.aop.framework.ObjenesisCglibAopProxy.createProxyClassAndInstance(ObjenesisCglibAopProxy.java:91) ~[spring-aop-6.1.12.jar!/:6.1.12]
        at org.springframework.aop.framework.CglibAopProxy.buildProxy(CglibAopProxy.java:221) ~[spring-aop-6.1.12.jar!/:6.1.12]
        ... 30 common frames omitted

Minimal sample application

build.gradle

plugins {
	id 'java'
	id 'org.springframework.boot' version '3.3.3'
	id 'io.spring.dependency-management' version '1.1.7'
}
group = 'com.example'
version = '0.0.1-SNAPSHOT'
java {
	toolchain {
		languageVersion = JavaLanguageVersion.of(17)
	}
}
configurations {
	compileOnly {
		extendsFrom annotationProcessor
	}
}
repositories {
	mavenCentral()
}
dependencies {
	implementation 'org.springframework.boot:spring-boot-starter'
	implementation 'org.springframework.boot:spring-boot-starter-web'
	implementation 'org.springframework.boot:spring-boot-starter-aop'
	implementation 'org.springframework:spring-core'
	compileOnly 'org.projectlombok:lombok'
	annotationProcessor 'org.projectlombok:lombok'
}
tasks.named('test') {
	useJUnitPlatform()
}

DemoApplication.java

@SpringBootApplication
public class DemoApplication {
  public static void main(String[] args) {
    URLClassLoader classLoader = new URLClassLoader(new URL[0], Thread.currentThread().getContextClassLoader());
    SpringApplication app = new SpringApplication(new DefaultResourceLoader(classLoader), DemoApplication.class);
    app.run(args);
  }
}

SomeConfig.java

@Configuration
public class SomeConfig {
}

SomeService.java

@Service
public class SomeService {

  private final SomeConfig config;

  @Lazy
  public SomeService(SomeConfig config) {
    this.config = config;
  }

}

Possible way to fix

This happens because Enhancer, that creates Configuration does not respect provided custom class loader.

In ConfigurationClassEnhancer in method newEnhancer it does not call enhancer.setClassLoader(classLoader)
In the same time CglibAopProxy respects provided custom class loader, it sets classloader in buildProxy method

if (classLoader != null) {
  enhancer.setClassLoader(classLoader);
...

There is also cache in AbstractClassGenerator, where key is ClassLoader:
private static volatile Map<ClassLoader, ClassLoaderData> CACHE = new WeakHashMap<>();
When Spring loads configuration class the first time, it does not use custom classloader and key is the default classloader (method create in AbstractClassGenerator).
When Spring creates cglib proxy for the configuration class, it calles create again, but this time custom class loader set to classLoader field, so the key in the CACHE is different. And this causes the issue.
This probably could be fixed if enhanchers for the same class will always use the same class loader.

For example you can set classloader in ConfigurationClassEnhancer -> newEnhancer method. I tried to do it in debug and it seems to work.

[snicoll]

@AlexanderShchelkunov Thanks for the report. Please move all that text into a sample we can actually run ourselves. You can attach a zip to this issue or push the code to a GitHub repository.

[AlexanderShchelkunov]

@AlexanderShchelkunov Thanks for the report. Please move all that text into a sample we can actually run ourselves. You can attach a zip to this issue or push the code to a GitHub repository.

Hi @snicoll,
Please see the attached file.

demo.zip