As java application deployed is base on the filename of your war file, if you wish to deploy your java application to httpdoc folder so that when user visit your website (example, domain.com) it will load, please note that this will not be possible currently.
However you can redirect user to the java application when user visit your website by creating a simple .htaccess file
Kindly follow the guide below on how to create a .htaccess file and the code to put in
- Login to your Plesk control
- Click on "File Manager"

- Click on "New" > "Create File"

- Type ".htaccess" and click on "OK"

- Click on ".htaccess"

- Copy and paste the following code:
RewriteEngine on
RewriteCond %{HTTP_HOST} ^domain.org.com$
RewriteRule (.*) http://domain.org/$1 [R=301,L]
RewriteRule ^$ mysite [L]
NOTE: Change domain.org to your domain and do not remove the .com. Change mysite to your war filename.

- Use another browser to test by visiting your website to ensure it works.