The paradigm of MangoDB and Oracle are totally different. The only similarity is both are databases.
MangoDB stored data in key - value form, while Oracle can have full fledged schema/table structure. For migrating data from MangoDB to Oracle you need to design the schema in Oracle DB taking RDBMS concepts into mind. Then you can write a java program which can be something like:
1. One component of your application will connect to MangoDB and will fetch the data from there.
2. Second component will parse the data and convert it into objects or appropriate form so that it can be added to Oracle.
3. Third component will insert the validated data into Oracle database tables.
If you need help designing & coding then you can contact me.