Oracle ADF is a popular development framework for building Java based applications, it especially excels in building applications that work with databases.

Oracle Application Builder Cloud Service has a special features that enables you to quickly incorporate REST services exposed by the Oracle ADF Business Components layer as objects in ABCS.

In the video/blog below you can see the full process of doing this.

This is a great easy way to get access to data from external databases into and Oracle ABCS application.