Cannot subclass final class com.sun.proxy.$Proxy202

[spring-projects-issues]

FrostbittenKing opened BATCH-2821 and commented

I fail to correctly use the RepositoryMethodReference with the RepositoryItemReaderBuilder.

After I found your sample tests (they are only unit tests), i tried it in an actual spring boot batch application, but the application always terminates on startup, when it tries to instantiate the bean for.

 

-- Snip
Caused by: org.springframework.beans.BeanInstantiationException: Failed to instantiate [org.springframework.batch.item.data.RepositoryItemReader]: Factory method 'reader' threw exception; nested exception is java.lang.IllegalArgumentException: Cannot subclass final class com.sun.proxy.$Proxy202Caused by: org.springframework.beans.BeanInstantiationException: Failed to instantiate [org.springframework.batch.item.data.RepositoryItemReader]: Factory method 'reader' threw exception; nested exception is java.lang.IllegalArgumentException: Cannot subclass final class com.sun.proxy.$Proxy202 at org.springframework.beans.factory.support.SimpleInstantiationStrategy.instantiate(SimpleInstantiationStrategy.java:185) at org.springframework.beans.factory.support.ConstructorResolver.instantiateUsingFactoryMethod(ConstructorResolver.java:583) ... 64 common frames omittedCaused by: java.lang.IllegalArgumentException: Cannot subclass final class com.sun.proxy.$Proxy202 at org.springframework.cglib.proxy.Enhancer.generateClass(Enhancer.java:565) at org.springframework.cglib.core.DefaultGeneratorStrategy.generate(DefaultGeneratorStrategy.java:25) at org.springframework.cglib.core.AbstractClassGenerator.generate(AbstractClassGenerator.java:329) at org.springframework.cglib.proxy.Enhancer.generate(Enhancer.java:492) at org.springframework.cglib.core.AbstractClassGenerator$ClassLoaderData$3.apply(AbstractClassGenerator.java:93) at org.springframework.cglib.core.AbstractClassGenerator$ClassLoaderData$3.apply(AbstractClassGenerator.java:91) at org.springframework.cglib.core.internal.LoadingCache$2.call(LoadingCache.java:54) at java.util.concurrent.FutureTask.run(FutureTask.java:266) at org.springframework.cglib.core.internal.LoadingCache.createEntry(LoadingCache.java:61) at org.springframework.cglib.core.internal.LoadingCache.get(LoadingCache.java:34) at org.springframework.cglib.core.AbstractClassGenerator$ClassLoaderData.get(AbstractClassGenerator.java:116) at org.springframework.cglib.core.AbstractClassGenerator.create(AbstractClassGenerator.java:291) at org.springframework.cglib.proxy.Enhancer.createHelper(Enhancer.java:480) at org.springframework.cglib.proxy.Enhancer.create(Enhancer.java:305) at org.springframework.batch.item.data.builder.RepositoryItemReaderBuilder$RepositoryMethodReference.methodIs(RepositoryItemReaderBuilder.java:270) at sample.batch.jobs.SampleJob.reader(SampleJob.java:124) at sample.batch.jobs.SampleJob$$EnhancerBySpringCGLIB$$879fb0c0.CGLIB$reader$4(<generated>) at sample.batch.jobs.SampleJob$$EnhancerBySpringCGLIB$$879fb0c0$$FastClassBySpringCGLIB$$f29d5ef8.invoke(<generated>) at org.springframework.cglib.proxy.MethodProxy.invokeSuper(MethodProxy.java:228) at org.springframework.context.annotation.ConfigurationClassEnhancer$BeanMethodInterceptor.intercept(ConfigurationClassEnhancer.java:365) at sample.batch.jobs.SampleJob$$EnhancerBySpringCGLIB$$879fb0c0.reader(<generated>) at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method) at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:62) at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43) at java.lang.reflect.Method.invoke(Method.java:498) at org.springframework.beans.factory.support.SimpleInstantiationStrategy.instantiate(SimpleInstantiationStrategy.java:154) ... 65 common frames omitted

Sorry, cannot list the complete stacktrace (work-related).

I'm not sure how this is supposed to work, since the class gets proxied (and as documented) cannot be final, but this is a Repository Interface extending JpaRepository, which makes it final by design, as far as I understand.

I'm sorry for asking but was this ever tested outside a unit test?

 

Following sample fails, and blows up with a stacktrace similar to the one listed above:

@Repository
public interface SampleRepository extends JpaRepository<JpaSample,Long>
{
// ...
}

public class SampleReaderIT extends AbstractIntegrationTest // common base class for spring full blown integration tests
{
     @Test
     public void sampleTest() throws Exception
     {
         RepositoryItemReaderBuilder.RepositoryMethodReference<SampleRepository> methodReference =
            new RepositoryItemReaderBuilder.RepositoryMethodReference<>(sampleRepository);        methodReference.methodIs().getOne(null);        new RepositoryItemReaderBuilder<JpaSample>()
            .repository(methodReference)
            .pageSize(100)
            .saveState(false)
            .sorts(MapUtils.putAll(new HashMap<>(), new Object[][]`"id", Sort.Direction.ASC`))
            .build();
     }
}

---

No further details from BATCH-2821

The problem is in the method RepositoryItemReaderBuilder.RepositoryMethodReference#methodIs:

spring-batch/spring-batch-infrastructure/src/main/java/org/springframework/batch/item/data/builder/RepositoryItemReaderBuilder.java

Lines 279 to 284 in 5c57ed4

	public T methodIs() {
	Enhancer enhancer = new Enhancer();
	enhancer.setSuperclass(this.repository.getClass());
	enhancer.setCallback(this.repositoryInvocationHandler);
	return (T) enhancer.create();
	}

The enhancer.create() call fails with an error:

java.lang.IllegalArgumentException: Cannot subclass final class com.sun.proxy.$Proxy202

because the actual repository object is proxied.

How could we fix this?

Could we use ClassUtils.getUserClass(Class) or AopUtils.getTargetClass(Object) in RepositoryMethodReference in order to determine the real repository class declared by user and then create an Enhancer for it?

Another solution would be to pass the repository's Class as a constructor argument into RepositoryMethodReference.

[00010001]

I hit the same issue but found workaround https://stackoverflow.com/questions/72041358/spring-batch-repositoryitemreaderbuilder-with-repositorymethodreference-throws/72086071#72086071