In testing against the v18.4.0-xe docker image with the ojdbc8.jar I am finding the following connection strings working in Ignition:
jdbc:oracle:thin:@localhost:1521:XE
jdbc:oracle:thin:@10.0.1.153:1521:XE #Just in case localhost is a special case
jdbc:oracle:thin:@<hostname>:1521:XE #Just to confirm my hostname works with same syntax
#Formatting you recommended
jdbc:oracle:thin:@//<hostname>:1521/XE
jdbc:oracle:thin:@<hostname>:1521/XE
It could be something with the DB version, but 12 is only about 5 years old if I remember correctly and I don't think the connection strings have changed in that time. Are there any special or non-ASCII characters in either the hostname or the SID?
One thing I did find odd is this syntax faults with a port error despite Oracle claiming it should work:
jdbc:oracle:thin:@//<hostname>:1521:XE
Edit:
Looks like for SIDs / and : work. If you are using a service name, then only / will work
As I had no clue about being different types of connections for Oracle, this article looks to explain the differences: