My initial suspicion is that the initial setup didn't include the fully qualified name, but check for certain with the following statement:
SELECT ag.NAME AS "Availability Group"
,ar.replica_server_name AS "When Primary Replica Is"
,rl.routing_priority AS "Routing Priority"
,ar2.replica_server_name AS "RO Routed To"
FROM sys.availability_read_only_routing_lists rl
INNER JOIN sys.availability_replicas ar ON rl.replica_id = ar.replica_id
INNER JOIN sys.availability_replicas ar2 ON rl.read_only_replica_id = ar2.replica_id
INNER JOIN sys.availability_groups ag ON ar.group_id = ag.group_id
ORDER BY ag.NAME
The query was gratuitously lifted from this MSDN blog: https://blogs.msdn.microsoft.com/alwaysonpro/2014/01/22/modifying-alwayson-read-only-routing-lists/
In addition, make sure your JDBC driver supports the ApplicationIntent=ReadOnly parameter.