IllegalAccessError: Class ref in pre-verified class resolved to unexpected implementation on Android 4.3.1 and Jackson 2.12.0

[johnjohndoe]

Describe the bug

• I discovered an IllegalAccessError: Class ref in pre-verified class resolved to unexpected implementation when I run this Android app in the following environment:

  • Android emulator, Nexus 5X, Intel x86 Atom, system-images;android-18;google_apis;x86, revision: 6
  • Android 4.3.1 (API level 18, Jelly Bean)
  • no Google Play Services installed
  • crash occured in DEBUG build, RELEASE build not tested yet
  • com.fasterxml.jackson.core:jackson-databind:2.12.0

Version information

• com.fasterxml.jackson.core:jackson-databind:2.12.0 - 2.12.3

To Reproduce

1. Clone the project
2. Set up an Android emulator and start it
3. Run all instrumentation tests via ./gradlew connectedAndroidTest

Observed behavior

• Four tests fails with the following error:

> Task :Umweltzone:connectedDebugAndroidTest
Starting 26 tests on API_18_4.3_Nexus_5_x86(AVD) - 4.3.1

de.avpptr.umweltzone.utils.ContentProviderTest > testGetAdministrativeZones_worksAtAll[API_18_4.3_Nexus_5_x86(AVD) - 4.3.1] FAILED 
  java.lang.IllegalAccessError: Class ref in pre-verified class resolved to unexpected implementation
  at com.fasterxml.jackson.databind.deser.std.CollectionDeserializer.createContextual(CollectionDeserializer.java:198)

de.avpptr.umweltzone.utils.ContentProviderTest > testGetCircuits_usesCaches[API_18_4.3_Nexus_5_x86(AVD) - 4.3.1] FAILED 
  java.lang.IllegalAccessError: Class ref in pre-verified class resolved to unexpected implementation
  at com.fasterxml.jackson.databind.deser.std.CollectionDeserializer.createContextual(CollectionDeserializer.java:198)

de.avpptr.umweltzone.utils.ContentProviderTest > testGetFaqs_worksAtAll[API_18_4.3_Nexus_5_x86(AVD) - 4.3.1] FAILED 
  java.lang.IllegalAccessError: Class ref in pre-verified class resolved to unexpected implementation
  at com.fasterxml.jackson.databind.deser.std.CollectionDeserializer.createContextual(CollectionDeserializer.java:198)

de.avpptr.umweltzone.utils.ContentProviderTest > testGetCircuits_worksAtAll[API_18_4.3_Nexus_5_x86(AVD) - 4.3.1] FAILED 
  java.lang.IllegalAccessError: Class ref in pre-verified class resolved to unexpected implementation
  at com.fasterxml.jackson.databind.deser.std.CollectionDeserializer.createContextual(CollectionDeserializer.java:198)

• See also this Travis CI log.

Stacktrace

java.lang.IllegalAccessError: Class ref in pre-verified class resolved to unexpected implementation
  at com.fasterxml.jackson.databind.deser.std.CollectionDeserializer.createContextual(CollectionDeserializer.java:198)
  at com.fasterxml.jackson.databind.deser.std.CollectionDeserializer.createContextual(CollectionDeserializer.java:28)
  at com.fasterxml.jackson.databind.DeserializationContext.handlePrimaryContextualization(DeserializationContext.java:765)
  at com.fasterxml.jackson.databind.deser.BeanDeserializerBase.resolve(BeanDeserializerBase.java:535)
  at com.fasterxml.jackson.databind.deser.DeserializerCache._createAndCache2(DeserializerCache.java:293)
  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.findContextualValueDeserializer(DeserializationContext.java:558)
  at com.fasterxml.jackson.databind.deser.std.CollectionDeserializer.createContextual(CollectionDeserializer.java:188)
  at com.fasterxml.jackson.databind.deser.std.CollectionDeserializer.createContextual(CollectionDeserializer.java:28)
  at com.fasterxml.jackson.databind.DeserializationContext.handleSecondaryContextualization(DeserializationContext.java:796)
  at com.fasterxml.jackson.databind.DeserializationContext.findRootValueDeserializer(DeserializationContext.java:596)
  at com.fasterxml.jackson.databind.ObjectMapper._findRootDeserializer(ObjectMapper.java:4731)
  at com.fasterxml.jackson.databind.ObjectMapper._readMapAndClose(ObjectMapper.java:4592)
  at com.fasterxml.jackson.databind.ObjectMapper.readValue(ObjectMapper.java:3599)
  at de.avpptr.umweltzone.utils.ContentProvider.getContent(ContentProvider.java:120)
  at de.avpptr.umweltzone.utils.ContentProvider.getContent(ContentProvider.java:98)
  at de.avpptr.umweltzone.utils.ContentProvider.getAdministrativeZones(ContentProvider.java:74)
  at de.avpptr.umweltzone.utils.ContentProviderTest.testGetAdministrativeZones_worksAtAll(ContentProviderTest.java:133)

See: if ((!Objects.equals(unwrapSingle, _unwrapSingle)) at jackson-databind/CollectionDeserializer.java#L198

Expected behavior

• No exception. Tests succeed.

Additional context

• Tests succeed when com.fasterxml.jackson.core:jackson-databind:2.11.3 is used.
  • See also this Travis CI log.

Related

• Issue #2599: NoClassDefFoundError at DeserializationContext. on Android 4.1.2 and Jackson 2.10.0
• Issue #1802: NoClassDefFoundError/ExceptionInInitializerError on Android 2.3.3 and Jackson 2.9.0

[cowtowncoder]

I don't know what causes this, although suggestions from earlier issues suggest it might use of java.util.Objects; specifically Objects.equals().
This method is part of JDK 1.7 and is legal to use as per Jackson baseline; no change will be made to remove it.

So it might just be a limitation for use of Jackson with older versions of Android SDK at this point.

Jackson 2.13 will require Java 8 baseline.

[cowtowncoder]

Looks like java.util.Objects was added in Android API level 19 (Android 4.4):

https://developer.android.com/reference/kotlin/java/util/Objects

Jackson-databind did use this method in one place in 2.11, but much more extensively in 2.12.

I will add a note about this on 2.12 release notes:

https://github.com/FasterXML/jackson/wiki/Jackson-Release-2.12

now. Also note that officially JDK 7 has been required since Jackson 2.8:

https://github.com/FasterXML/jackson/wiki/Jackson-Release-2.8

[johnjohndoe]

Jackson-databind did use this method in one place in 2.11, but much more extensively in 2.12.

I found not too many places where Objects.equal is used. Did you consider using a compatibility wrapper inspired by ObjectsCompat from the androidx-core library?

[cowtowncoder]

I was not aware of this being a compatibility concern so choice to use this method was for convenience, and not a conscious decision. But the way it turned out, I think, is that minimum baseline usable on Android was bumped from 18 to 19.
I don't think it worth trying to unroll this at this point in time.

What would be useful, however, would be some sort of test suite that could uncover such changes: something like jackson-android-compatibility-tests project, which could be run against Jackson versions. This to identify changes during release candidate phase.

[johnjohndoe]

... minimum baseline usable on Android was bumped from 18 to 19 ...

Do you mean: as an unintentional side effect?

What would be useful, however, would be some sort of test suite that could uncover such changes: something like jackson-android-compatibility-tests project, which could be run against Jackson versions. This to identify changes during release candidate phase.

I totally agree. That would be very valuable. That is how I discovered the issue myself. I use Travis CI to execute instrumentation tests (running Android emulator, android-18 in particular). That is possible with different CI systems as far as I know. I believe it would be sufficient to create a very basic Android project, add a few Android instrumentation tests and then set up the CI configuration. I have seen configurations which target different Android versions (build matrix). This would allow testing against Android SDK 18, 19, ...

[cowtowncoder]

Correct, unintentional/unplanned change.
And yes, output on supported levels would be valuable so users could verify compatibility. This could also guide maintenance status of branches: just as an example it could make it more likely that certain branch could get patches longer than otherwise.

[johnjohndoe]

Is my open source project, my open source CI configuration and the links enough information for you to set it up?

[cowtowncoder]

That would be helpful for sure -- either me (if and when I have time), or perhaps someone else who would be interested in improving Android compatibility. I could ask on jackson-dev mailing list and twitter for collaborators. Just so that I won't become the main bottleneck.

[johnjohndoe]

Sounds good to me. Feel free to ping me if I can be of help.