Android 9 (API 28) compatibility

[bemasc]

Caffeine currently cannot be used in apps that target Android 9 (API 28), because Android 9 blocks access to threadLocalRandomProbe as part of the restrictions on non-SDK interfaces.

For more details see micronaut-projects/micronaut-core#124 (comment)

[ben-manes]

True, it is lightly touched on in the Guava compatibility, although the reason has changed now. It is not a goal of this project to run on Android.

However, I think we could provide graceful fallback such as to ThreadLocal for broader compatibility. It won't be a goal of this project to target & optimize for Android, though.

[bemasc]

Thanks, that sounds like a good plan.

Android does support Java 8, and indeed is running on OpenJDK 8, so perhaps you should revise the rationale there. Caffeine currently works fine on Android API 24-27, but not 28.

[ben-manes]

Closing because neither of us originally considered the DEX issue.

Since we codegen to reduce memory footprint, that's good for servers and more troublesome for Android. Users would have to use Proguard and know which classes to keep, which is flaky and annoying. I think Android requires so many different design considerations that Caffeine will never be a good fit. Another library or your custom implementation seems to make a lot more sense.