The latest release of iCal4j includes caching of VTimezone definitions used to populate the TimeZoneRegistry. This will improve load times due to reduced IO and network utilisation.
As a result of this caching a new dependency on the jcache API has been introduced. This means you will need to include an implementation of a jcache CachingProvider in your runtime dependencies. Typically this is as easy as adding one of the well-known cache dependencies (e.g. ehcache, hazelcast, ignite, etc.), but you can also provide more sophisticated caching configurations as required. Note that the ical4j timezone cache is called “ical4j.timezones”.
A list of possible caching provider implementations is available from the JCACHE website.