GeoServer depends on two different version of the json-lib library (2.1 and 2.2.3).
The 2.1 version comes from GeoWebCache (https://github.com/GeoWebCache/geowebcache/blob/master/geowebcache/pom.xml) while the 2.2.3 version comes from GeoServer itself (https://github.com/geoserver/geoserver/blob/master/src/pom.xml).
This pull requests adds an exclusion to the GWC json-lib dependency. This is necessary to get GeoScript Groovy working with the community script module.
Exclude old json-lib version from GWC
Backport of pull request #55
a bit late, but sounds good to me. Mind creating a GWC ticket to upgrade the json-lib version (and any other that geoserver has more current for that matter). TIA