JDK 16 Illegal reflective access for `Throwable.setCause()` with `PropertyNamingStrategy.UPPER_CAMEL_CASE`

Describe the bug Mapping a json string to an instance of RuntimeException with JDK 16 (which defaults to denying illegal reflective access) while using UPPER_CAMEL_CASE property naming strategy, fails with:

Exception in thread "main" com.fasterxml.jackson.databind.exc.InvalidDefinitionException: Failed to call `setAccess()` on Method 'setCause' due to `java.lang.reflect.InaccessibleObjectException`, problem: Unable to make final void java.lang.Throwable.setCause(java.lang.Throwable) accessible: module java.base does not "opens java.lang" to unnamed module

This manifests in parts of the AWS v1 SDK when an error is received from the AWS API endpoints. Note example report: https://github.com/FasterXML/jackson-databind/issues/2464#issuecomment-856996757

The simplified reproduce case below is based on what the failing AWS SDK code is doing internally in com.amazonaws.transform.JsonErrorUnmarshaller.unmarshall.

Version information 2.12.3, 2.12.5, 2.13.0-rc2

To Reproduce Execute this code without any --add-opens params and with default --illegal-access setting of deny.

public class Test {
	public static void main(String[] args) throws Exception {
		ObjectMapper mapper = new ObjectMapper();
		mapper.setPropertyNamingStrategy(PropertyNamingStrategies.UPPER_CAMEL_CASE);

		String jsonString = "{\"message\":\"This is my runtime exception message\"}";
		JsonNode jsonContent = mapper.readTree(jsonString);

		throw mapper.treeToValue(jsonContent, RuntimeException.class);
	}
}

Expected behavior It is expected that the code above would throw a RuntimeException with a message of “This is my runtime exception message”. This is what happens when working around the issue with java parameter --add-opens java.base/java.lang=ALL-UNNAMED

Additional context Using java parameter --illegal-access=debug results in the following additional info:

WARNING: Illegal reflective access by com.fasterxml.jackson.databind.util.ClassUtil (file:/xxxxxx/jackson-databind-2.13.0-rc2.jar) to method java.lang.Throwable.setCause(java.lang.Throwable)
	at com.fasterxml.jackson.databind.util.ClassUtil.checkAndFixAccess(ClassUtil.java:994)
	at com.fasterxml.jackson.databind.introspect.AnnotatedMember.fixAccess(AnnotatedMember.java:139)
	at com.fasterxml.jackson.databind.deser.impl.MethodProperty.fixAccess(MethodProperty.java:95)
	at com.fasterxml.jackson.databind.deser.BeanDeserializerBuilder._fixAccess(BeanDeserializerBuilder.java:522)
	at com.fasterxml.jackson.databind.deser.BeanDeserializerBuilder.build(BeanDeserializerBuilder.java:373)
	at com.fasterxml.jackson.databind.deser.BeanDeserializerFactory.buildThrowableDeserializer(BeanDeserializerFactory.java:455)
	at com.fasterxml.jackson.databind.deser.BeanDeserializerFactory.createBeanDeserializer(BeanDeserializerFactory.java:112)
	at com.fasterxml.jackson.databind.deser.DeserializerCache._createDeserializer2(DeserializerCache.java:415)
	at com.fasterxml.jackson.databind.deser.DeserializerCache._createDeserializer(DeserializerCache.java:350)
	at com.fasterxml.jackson.databind.deser.DeserializerCache._createAndCache2(DeserializerCache.java:264)
	at com.fasterxml.jackson.databind.deser.DeserializerCache._createAndCacheValueDeserializer(DeserializerCache.java:244)
	at com.fasterxml.jackson.databind.deser.DeserializerCache.findValueDeserializer(DeserializerCache.java:142)
	at com.fasterxml.jackson.databind.DeserializationContext.findRootValueDeserializer(DeserializationContext.java:642)
	at com.fasterxml.jackson.databind.ObjectMapper._findRootDeserializer(ObjectMapper.java:4751)
	at com.fasterxml.jackson.databind.ObjectMapper._readValue(ObjectMapper.java:4596)
	at com.fasterxml.jackson.databind.ObjectMapper.readValue(ObjectMapper.java:2815)
	at com.fasterxml.jackson.databind.ObjectMapper.treeToValue(ObjectMapper.java:3279)
	at Test.main(Test.java:13)

Note that the issue does not manifest without mapper.setPropertyNamingStrategy(PropertyNamingStrategies.UPPER_CAMEL_CASE);

[cowtowncoder]

@yawkat Ok. Just didn’t see it in JDK javadocs; I guess only public (and maybe protected methods are included).

@gsinghlulu yes, correct on both accounts. I think fix is along the right lines; will see if we could first remove setCause() if it exists (or replace it). I am only hesitant about looking at Cause in case other translations might miss it. But it might be good enough too, either way thank you for providing it!

[cowtowncoder]

Ok, yes, JDK 12 added Throwable.setCause() apparently.

This specific issue now fixed in 2.13 (for 2.13.4, then 2.14.0). But I think there is the follow-up issue of PropertyNamingStrategy not working for Throwable, will file separate issue for that.