Is there any good way to save the sortorder?

In the example , I found that there is a sort field in the source code named ‘sortorder’ .

How to maintain this sequence after drag and drop in real time and how to save it ?

Is there demo with Java and JSP?

Hello,
Gantt doesn’t have a built-in way to save that data on the server. You need to manually implement a custom solution.
We have the following article that describes what you need to do:
https://docs.dhtmlx.com/gantt/desktop__server_side.html#storingtheorderoftasks

We don’t have any guides for Java, but there are guides with ready demos for other frameworks:
https://docs.dhtmlx.com/gantt/desktop__howtostart_php.html#storingtheorderoftasks
https://docs.dhtmlx.com/gantt/desktop__howtostart_php_laravel.html#storingtheorderoftasks
https://docs.dhtmlx.com/gantt/desktop__howtostart_nodejs.html#storingtheorderoftasks
https://docs.dhtmlx.com/gantt/desktop__howtostart_dotnet.html#storingtheorderoftasks
https://docs.dhtmlx.com/gantt/desktop__howtostart_ruby.html#storingtheorderoftasks