There's a complete soup to nuts post from Deepak Vohra on the Oracle community pages of ToadWorld on loading a fixed length file into the Oracle database. This post is interesting from a few fronts; firstly this is the out of the box experience, no specialized KMs so just basic integration from getting the software installed to running a mapping. Also it demonstrates fixed length file integration including how to use the ODI UI to define the fields and pertinent properties.

 Check the blog post out below....

http://www.toadworld.com/platforms/oracle/w/wiki/10935.loading-text-file-data-into-oracle-database-12c-with-oracle-data-integrator-12c.aspx

Hopefully you also find this useful, many thanks to Deepak for sharing his experiences. You could take this example further and illustrate how to load into Oracle using the LKM File to Oracle via External table knowledge module which will perform much better and also leverage such things as using wildcards for loading many files into the 12c database.