Question

how can I open a file from within a java program with a custom application?

Desktop.getDesktop().open(file);

opens the file only with the systems default application. What I need is something like

open(myapp, file);

Answer 1

If the target application accepts files to open as arguments, then you could do the following:

Runtime rt = Runtime.getRuntime();
Process proc = rt.exec("CustomApp "+filename);