ClassUtils.forName fails to load class from ContextTypeMatchClassLoader [SPR-17452]

[spring-projects-issues]

Christoph Empl opened SPR-17452 and commented

#21867 changed the implementation of ClassUtils#forName: classloading is implemented with Class#forName instead of Classloader#loadClass.

 Since this change one of our Spring-components ("ClassA") isn't found as an autowiring candidate for an interface ("InterfaceA") anymore:
Class.forName("ClassA", false, clToUse) 
clToUse: (e.g.)

org.springframework.context.support.ContextTypeMatchClassLoader@34d89c26

Results in: ClassA - its classloader is another instance of  ContextTypeMatchClassLoader: (e.g.)

org.springframework.context.support.ContextTypeMatchClassLoader$ContextOverridingClassLoader@3a2db42b

This classloader has two loaded classes: InterfaceA and ClassA.

In contrast, clToUse.loadClass("ClassA") returns the expected result:
ClassA, its classloader is the parent of clToUse 

 
The affected project uses openjdk 11 (11+28). 

The somehow weird behaviour of Class#forName is already mentioned in #18631 and #7300.

 

 

 

---

Affects: 5.1.1, 5.1.2

Issue Links:

• ClassUtils.forName() performance [SPR-14059] #18631 ClassUtils.forName() performance
• ClassUtils could use long form of Class.forName [SPR-17333] #21867 ClassUtils could use long form of Class.forName
• Class.forName() produces different results to ClassLoader.loadClass() in certain circumstances [SPR-2611] #7300 Class.forName() produces different results to ClassLoader.loadClass() in certain circumstances

Referenced from: commits 5cd525a

[spring-projects-issues]

Juergen Hoeller commented

So Class.forName still has issues even on modern-day JVMs... what a shame, in particular since it is an important enabler on GraalVM.

Are you using load-time weaving there? That's pretty much the only reason to use ContextTypeMatchClassLoader...

I suppose we'll have to differentiate in our ClassUtils.forName implementation, only delegating to ClassUtils.forName for standard ClassLoader arrangements.

[spring-projects-issues]

Christoph Empl commented

Yes, i'm using load time weaving.

[spring-projects-issues]

Juergen Hoeller commented

We're enforcing the use of ClassLoader.loadClass in case of a temporary ClassLoader now, as well as in case of a dynamically re-resolved class name from a SpEL expression. This will be available in the upcoming 5.1.3.BUILD-SNAPSHOT should hopefully address your regression.

[spring-projects-issues]

Christoph Empl commented

With the latest build snapshot the application starts fine and the affected Spring component is correctly identified as an autowiring candidate. Thank you!

[spring-projects-issues]

Juergen Hoeller commented

Good to hear :-) Hopefully this is the right balance now... We have yet to see whether other special class loading scenarios are affected as well.