Based on Glink and the Glink API
Most existing mainframe applications are designed to communicate in 'forms mode' dialog with some kind of terminal. Gargen uses a development copy of Glink for Java Professional Edition to do the host communications, using the appropriate terminal type. Gargen drives this copy of Glink using the Glink for Java Application Programming Interface.
You can hand-program your own Java Beans for host communication using the Glink API, but programming of host communication Java Beans can be time-consuming, because of the trivial programmatical details of checking that the expected screen has been received, of selecting the data on the screen that you would like to be an output from your Java Bean and identifying the input that you want to enter, as constants for every execution of the Bean, or as variables to be taken from the input parameters to your Bean. Gargen automates this process.

Gargen is itself an example of the Glink API
Gargen is in control of the user interface, but uses the Glink API to drive a copy of Glink to do the interactions with the mainframe application. Gargen allows you to step through a mainframe application dialog sequence while recording the necessary information that a Java Bean will need in order to repeat the same function. Afterwards Gargen is able to generate the source code of a Java Bean or Enterprise Java Bean that uses the Glink API for mainframe communication and application forms processing.