Grails uses Spring Loaded for hot class reloading during run-app in development.
It’s open source but look like not actively developed (last commit was at october 2014). I had some issues with reloading on JVM 8. Also Spring Loaded has performance issues.
And the best tool for reloading is JRebel from estonian company ZeroTurnaround.
And you can use JRebel instead of Spring Loaded.
And few weeks ago, Anton Arhipov, technology evangelist of JRebel, in podcast said that they working on improvement of JRebel integration with Grails 2 for one customer. But they are not interested because Grails 3 will use a Spring Boot, and JRebel already has a good support of it.
So, lets wait 🙂
By the way JRebel has a new update 6 with a huge improvement of performance.