[SOLVED] Unix Cron validation: Not less than every 30 minutes

Issue

I'm very new to cron expression. I have only a basic understanding of how it works. I'm implementing an application that allows user to send in cron expression value with pattern * * * * * *. But the application will not allow cron to run less than once every 30 minutes.

This is the validation method I wrote.

private boolean checkInvalidCronExpresstion(final String value){
    final String[] expression = StringUtils.split( value, " " );
    // not allow case "* * * * * *"
    if (expression[0].equals( "*" )){
        return true;
    } else if ( expression[0].contains( "/" ) ){
        final String[] minutes = StringUtils.split( expression[0], "/" );
        diff = Integer.parseInt( minutes[1] );
        // not allow case "*/x * * * * *" with x < 30
        if (diff < 30 && expression[1].contains("*")){
            return true;
        }
    }
    return false;
}

My questions are:

1. Does the method above cover all the invalid expression that will trigger cron less than every 30 minutes, and
2. I believe there could be a more elegant way to check the expression for example translate it into hours and minutes. I did look into Spring CronSequenceGenerator but I don't see it could help in this case.

Any utility class or solution recommended?

Solution

Don't reinvent the wheel here. Use a library such as cron-utils to parse the Cron expression and validate it.

https://github.com/jmrozanec/cron-utils

Answered By - ck1