how to opn jnlp files automatically after download
You could try this


right click a jnlp file
chose "Open With"
select "Other"
navigate to "System", "Library", "CoreServices"
scroll the list and pick "Java Web Start" (you may need to chose "Enable All Applications" in order to make that choice possible.
tick the "Always Open With" box.


It is not recommended to have a generic set up to open files downloaded from the web.

But you can set up a exception. 

Specify the Folder for the jnpl files download. 

Then create a Folder action to 

1- monitor for new files

2-open them