Spring Spring 4 ReflectUtil not compatible with jdk16

I maintain a library that has a Spring integration. We of course encourage users to run spring 5, but also run unit tests against spring4 to make sure we don't introduce regressions for users on old Spring.

As of jdk16, spring 4.3.30.RELEASE no longer works:

Caused by: java.lang.IllegalStateException: Cannot load configuration class: org.jdbi.v3.spring4.TestPluginInstall$Config
    at org.springframework.context.annotation.ConfigurationClassPostProcessor.enhanceConfigurationClasses(ConfigurationClassPostProcessor.java:404)
    at org.springframework.context.annotation.ConfigurationClassPostProcessor.postProcessBeanFactory(ConfigurationClassPostProcessor.java:249)
    at org.springframework.context.support.PostProcessorRegistrationDelegate.invokeBeanFactoryPostProcessors(PostProcessorRegistrationDelegate.java:283)
    at org.springframework.context.support.PostProcessorRegistrationDelegate.invokeBeanFactoryPostProcessors(PostProcessorRegistrationDelegate.java:127)
    at org.springframework.context.support.AbstractApplicationContext.invokeBeanFactoryPostProcessors(AbstractApplicationContext.java:687)
    at org.springframework.context.support.AbstractApplicationContext.refresh(AbstractApplicationContext.java:524)
    at org.springframework.test.context.support.AbstractGenericContextLoader.loadContext(AbstractGenericContextLoader.java:127)
    at org.springframework.test.context.support.AbstractGenericContextLoader.loadContext(AbstractGenericContextLoader.java:60)
    at org.springframework.test.context.support.AbstractDelegatingSmartContextLoader.delegateLoading(AbstractDelegatingSmartContextLoader.java:281)
    at org.springframework.test.context.support.AbstractDelegatingSmartContextLoader.loadContext(AbstractDelegatingSmartContextLoader.java:249)
    at org.springframework.test.context.cache.DefaultCacheAwareContextLoaderDelegate.loadContextInternal(DefaultCacheAwareContextLoaderDelegate.java:98)
    at org.springframework.test.context.cache.DefaultCacheAwareContextLoaderDelegate.loadContext(DefaultCacheAwareContextLoaderDelegate.java:116)
    ... 33 more

Caused by: java.lang.ExceptionInInitializerError
    at org.springframework.context.annotation.ConfigurationClassEnhancer.newEnhancer(ConfigurationClassEnhancer.java:122)
    at org.springframework.context.annotation.ConfigurationClassEnhancer.enhance(ConfigurationClassEnhancer.java:110)
    at org.springframework.context.annotation.ConfigurationClassPostProcessor.enhanceConfigurationClasses(ConfigurationClassPostProcessor.java:394)

Caused by: java.lang.reflect.InaccessibleObjectException: Unable to make protected final java.lang.Class java.lang.ClassLoader.defineClass(java.lang.String,byte[],int,int,java.security.ProtectionDomain) throws java.lang.ClassFormatError accessible: module java.base does not "opens java.lang" to unnamed module @5d20b857
    at java.base/java.lang.reflect.AccessibleObject.checkCanSetAccessible(AccessibleObject.java:357)
    at java.base/java.lang.reflect.AccessibleObject.checkCanSetAccessible(AccessibleObject.java:297)
    at java.base/java.lang.reflect.Method.checkCanSetAccessible(Method.java:199)
    at java.base/java.lang.reflect.Method.setAccessible(Method.java:193)
    at org.springframework.cglib.core.ReflectUtils$1.run(ReflectUtils.java:61)
    at java.base/java.security.AccessController.doPrivileged(AccessController.java:554)
    at org.springframework.cglib.core.ReflectUtils.<clinit>(ReflectUtils.java:52)
    at org.springframework.cglib.core.KeyFactory$Generator.generateClass(KeyFactory.java:243)
    at org.springframework.cglib.core.DefaultGeneratorStrategy.generate(DefaultGeneratorStrategy.java:25)
    at org.springframework.cglib.core.AbstractClassGenerator.generate(AbstractClassGenerator.java:329)
    ... 59 more

If Spring 4 is still supported, maybe some of the recent ReflectUtils jdk 16 changes from Spring 5 could be backported. Thanks!

Comment From: jhoeller

I'm afraid Spring Framework 4.3 has reached its EOL already: https://github.com/spring-projects/spring-framework/wiki/Spring-Framework-Versions There are no plans for further releases, and FWIW we never intended to officially support any JDK >8 in that line to begin with.

The ReflectUtil class is actually from CGLIB, repackaged into spring-core. The protected ClassLoader.defineClass method is still there in JDK 16, it just needs to be exported through --add-opens java.base/java.lang=ALL-UNNAMED on JVM startup. Even if we don't officially support JDK 16 with our 4.3.x line, it should work fine with that command line setting to the best of my understanding.

Comment From: stevenschlansker

OK, thanks, we will probably sunset our spring4 integration then and target 5+ only.

Comment From: jhoeller

Going 5+ is certainly the recommended path at this point. As an escape hatch for current 4.3 users, you can point them to --add-opens java.base/java.lang=ALL-UNNAMED (assuming that they control their JVM bootstrap settings) for the time being.