Finished reworking the Parser UI. It uses a split pane so you can get as much or as little space as you need. Features a text input area on the left with a parse button on the bottom, and a tree view on the right (to see the parsed packet contents) with a valid indicator on the bottom.
Nothing is hooked up yet to logic, so that is coming up soon on the list!
Swing is definitely kind of tedious to write though!

Check out the github: https://github.com/arnabmondal-eg/dnp3