Exclude sealed interfaces from auto-proxying (for JDK 17 compatibility)

[dreis2211]

Hi,

I recently opened an issue to track the needed stuff for Spring-Boot in order to support Java 17. spring-projects/spring-boot#26767. I think it makes sense to have the same for Spring Framework.

Known issues:

1. Sealed interfaces need to be handled e.g. when creating proxies.

@Bean
@Scope(proxyMode = ScopedProxyMode.INTERFACES)
String alpha() {
	return "alpha";
}

Essentially, under the hood it retrieves all interfaces of String here which also includes ConstantDesc which is a sealed interface and cannot be used when creating a proxy. See ScopedProxyFactoryBean.setBeanFactory:

if (!isProxyTargetClass() || beanType.isInterface() || Modifier.isPrivate(beanType.getModifiers())) {
        // This should filter sealed interfaces I guess
	pf.setInterfaces(ClassUtils.getAllInterfacesForClass(beanType, cbf.getBeanClassLoader()));
}

After a first look this probably needs to be handled more centrally and more places are potentially affected by sealed interfaces.

There is likely more to do for Java 17 support, but I wanted to kick this off. Feel free to add to this issue or repurpose it to only handle the specific issue.

Let me know if I can help.

Cheers,
Christoph

[jhoeller]

It seems sufficient to exclude sealed interfaces through a reflective Class.isSealed() check in the AopProxyUtils.completeProxiedInterfaces algorithm. I've locally tested this on JDK 17, seems to work fine so far. This will be in main for 5.3.9 tonight, would be great to know whether it also works for a Boot setup then...