You can use JDBC input plugin for getting the data from oracle database.
For that we have to provide path to JDBC driver, Connection string, User, Password, Schedule(Logstash will poll the DB based on the Cron), Statement(Query) etc., in the configuration.
it looks something like this:
I created logstash-ora.conf file in /etc/logstash/conf.d/ directory.
And placed required oracle connection string with credentials, and tried with a simple query , "select * from DUAL". And its working perfectly fine..
You can see in the below screenshot, "rawsearchdata" index got created!!