This appears to work OK, although there is a warning at startup:

WARNING: An illegal reflective access operation has occurred
WARNING: Illegal reflective access by org.codehaus.groovy.vmplugin.v7.Java7$1 (jar:file:/opt/apps/arthurs/arthurs.war!/WEB-INF/lib/groovy-2.5.6.jar!/) to constructor java.lang.invoke.MethodHandles$Lookup(java.lang.Class,int)
WARNING: Please consider reporting this to the maintainers of org.codehaus.groovy.vmplugin.v7.Java7$1
WARNING: Use --illegal-access=warn to enable warnings of further illegal reflective access operations
WARNING: All illegal access operations will be denied in a future release

This seems to be a Groovy level thing rather than something specific to my app. I'll see if it has any ramifications for the app itself.