I want to start Java GUI app on start up. Java app is server and is GUI and I want to start GUI on start up after login how to do this? Any ideas?
Since you talk about "after logging in", I assume you mean a graphical desktop environment. So after logging in how to start a Java application?
It depends on the desktop environment you're using, personally, I'm using XFCE, but I was a Gnome user for many years. Gnome has a session manager, that you could use to run a program after logging in, I suggest you look into that.
This article describes how to do that quite well.
If you're using KDE or something else, simply googling or using the help is usually enough.
On XFCE this is called "Session and Startup".