How to run .jar continually and automatically on Debian server?

Question

I have a .jar file I want to run all the time on a Debian server.

Currently I have figured out how to access the server via ssh on

Answer 1

Shell hooks are good for configuring user environment variables.

Cron is for scheduled jobs, mostly related maintenance, such as creating backups, managing log-files etc ...

Background processes with nohup as advised by Николай Митропольский, or ssh with "screen" application (which let you detach/reattach to a "session"), will be useful in development time.
But can not handle server shutdown cleanups, or respond to restarts.

Init scripts mentioned above is the standard way to start/stop services.

There is an application named init, which is the first application started when a Unix-like system boots.
Init, according to runlevel, starts some scripts, and those scripts manages daemons (services in Windows).
So for services, you write "hooks" for runlevels,

In Debian, /etc/init.d/ where you put your init scripts,
you can read the scripts inside this folder to get the idea,
they are text files (bash scripts).

Those scripts are called with an argument
(a standard keywords, such as "start", "stop" etc..).

/etc/rc?.d/ (where ? is one of runlevels), where the init finds the scripts to run.
But those scripts are just "automatically created" symbolic links to the scripts in /etc/init.d/.
You do not need to touch anything inside /etc/rc?.d/ folder.
*After putting your script into /etc/init.d/,
you only need to call to create symbolic links *:

sudo update-rc.d "your-scripts-name" defaults

As you see there are some prefixes attached to names of scripts; for example /etc/rc1.d/K10apache2 which is a symbolic link to /etc/init.d/apache2.
So a simple "ordered by name execution" is possible here.

Automatically creating those prefixes (so the execution order), dependency information is required.
So init scripts includes this information. Also information required when (at which runlevel) those scripts should be called (with "start" or "stop").

This dependency information is placed as comments in those scripts. Forexample apache server init script (/etc/init.d/apache2) includes those lines;

# Provides:          apache2
# Required-Start:    $local_fs $remote_fs $network $syslog $named
# Required-Stop:     $local_fs $remote_fs $network $syslog $named
# Default-Start:     2 3 4 5
# Default-Stop:      0 1 6

Detailed information exists in Debian policy;
https://www.debian.org/doc/debian-policy/ch-opersys.html#s-sysvinit also this will be usefull; https://refspecs.linuxbase.org/LSB_2.1.0/LSB-generic/LSB-generic/iniscrptfunc.html

NOTE: There is a huge transition and debates/fragmentations in Unix world.
Init and init scripts, tradationally used in Unix/Unix-like systems, nowadays becoming obsolete on many systems.
https://en.wikipedia.org/wiki/Init#Replacements_for_init
Debian currently uses systemd, but init scripts still works with systemd (systemd provides the compatibility).