从.jar文件触发特定类别的cron作业？

Question

I am running an AWS EC2 Linux instance, on which I uploaded a .jar file of a piece of software that I wrote. In order to trigger the app periodically, I want to use cron - and setup crontab in the following way:

23 12 * * * java -jar  /home/ec2-user/Cube-Core/Cube.jar > /home/ec2-user/CubeCore/CronLogfiles/test.log 2>&1

The paths all match, and I redirected the sysout and syserr from the software to a testlog file.

However: when cron does the job, what does he trigger within the jar itself? is he looking for a class called 'main' (that is just my assumption, since I am new to cron). If this is the case, how can I tell him explicitly which class to trigger, since my project's main class is called differently?

Also, I read only that some guys prefer to trigger a bash script with cron, and have the script itself trigger the .jar execution. I, on other hand, am telling crontab directly to execute the .jar. Which of these 2 ways is the 'cleanest' and why, or is it in the end just a matter of not overclutting the crontab entries?

Thank you all ,

Cheers

Answer 1

The Java tutorials indicate you need to define the entry point in the manifest:

Main-Class: classname

Depending on what you use to create your jar, there may be some configuration convenience to do that.

Good for you: you don't have to do anything special about the cron job. Not so good for you: it's done upon creating the jar, so if it's not there, that's quite a hassle.

But tbh, I'd suppose that if the jar works normally, there shouldn't be anything extra to do.

Answer 2

1. Jar with single Main class

java -jar myjar.jar` 

It will get the main class details from your meta file within your jar,

Main-class : com.yourpackage.Mainclass

2. Jar with more than one main class If you have more than one main class in your single jar then you can go with the below format,

java -cp myjar.jar MyClass