It's JBossCache class registered as eXo container component in configuration.xml file.
<component>
<key>org.jboss.cache.transaction.TransactionManagerLookup</key>
<type>org.jboss.cache.transaction.JBossStandaloneJTAManagerLookup</type>
</component>
JBossStandaloneJTAManagerLookup used in standalone environment. Bur for Application Server environment use GenericTransactionManagerLookup.