Spring cron expression for every after 30 minutes

Graphically, the cron syntax for Quarz is (source):

+-------------------- second (0 - 59)
|  +----------------- minute (0 - 59)
|  |  +-------------- hour (0 - 23)
|  |  |  +----------- day of month (1 - 31)
|  |  |  |  +-------- month (1 - 12)
|  |  |  |  |  +----- day of week (0 - 6) (Sunday=0 or 7)
|  |  |  |  |  |  +-- year [optional]
|  |  |  |  |  |  |
*  *  *  *  *  *  * command to be executed 

So if you want to run a command every 30 minutes you can say either of these:

0 0/30 * * * * ?
0 0,30 * * * * ?

You can check crontab expressions using either of these:

• crontab.guru — (disclaimer: I am not related to that page at all, only that I find it very useful). This page uses UNIX style of cron that does not have seconds in it, while Spring does as the first field.
• Cron Expression Generator & Explainer - Quartz — cron formatter, allowing seconds also.

According to the Quartz-Scheduler Tutorial It should be value="0 0/30 * * * ?"

The field order of the cronExpression is

1. Seconds
2. Minutes
3. Hours
4. Day-of-Month
5. Month
6. Day-of-Week
7. Year (optional field)

Ensure you have at least 6 parameters or you will get an error (year is optional).

<property name="cronExpression" value="0 0/30 * * * ?" />