exclude buildpack jar from classpath

[pborbas]

We are facing an issue on PWS. They upgraded to latest java buildpack 4.20 and our app started to through Jackson class related problems. It turned out that our app must us an older 2.5.3 jackson and the buildpack also puts a 2.7.0 jackson to the classpath. At startup it is random which one is found so 50% our app crashes.

I logged the source jars:
2019-08-23T09:58:59.16+0200 [APP/PROC/WEB/0]OUT 07:58:59.156 [main] INFO c.t.core.common.util.ClassUtil - Class class com.fasterxml.jackson.databind.ObjectMapper was loaded from: jar:file:/home/vcap/app/lib/spring_auto_reconfiguration-2.7.0_RELEASE.jar!/com/fasterxml/jackson/databind/ObjectMapper.class 2019-08-23T09:58:59.16+0200 [APP/PROC/WEB/0]OUT 07:58:59.164 [main] INFO c.t.core.common.util.ClassUtil - Class interface com.fasterxml.jackson.annotation.JsonInclude was loaded from: jar:file:/home/vcap/app/lib/spring_auto_reconfiguration-2.7.0_RELEASE.jar!/com/fasterxml/jackson/annotation/JsonInclude.class

It is really bad, since now our app is dependent on the buildpack version. Any solution for this?
I tried to switch to older version but then I get errors like:

2019-08-23T11:36:30.57+0200 [STG/0] OUT Downloaded app package (39.5M) 2019-08-23T11:36:31.75+0200 [STG/0] ERR [Buildpack] ERROR Compile failed with exception #<RuntimeError: Open JDK Like Memory Calculator error: No version resolvable for '2.0.2_RELEASE' in 3.13.0_RELEASE> 2019-08-23T11:36:31.75+0200 [STG/0] ERR Open JDK Like Memory Calculator error: No version resolvable for '2.0.2_RELEASE' in 3.13.0_RELEASE 2019-08-23T11:36:31.75+0200 [STG/0] ERR Failed to compile droplet: Failed to compile droplet: exit status 1 2019-08-23T11:36:31.81+0200 [STG/0] OUT Exit status 223

[nebhale]

This was handled as part of a fix to auto-reconfiguration and released as part of auto-reconfiguration 2.8.0. It will go out as part of 4.21 once we get the final issue complete.