> grails set-grails-version 2.4.4
I also created a new appliction with grails 2.4.4. From this application I took the BuildConfig.groovy and copied the content into to the BuildConfig.groovy of the application I wanted to update. Then I added the changes to the BuildConfig which are necessary for the application.
In the datasource of the application I had to change my current setting for hibernate which pointed default to Hibernate 3 so it will point to hibernate 4.
So I commented:
//cache.region.factory_class = 'net.sf.ehcache.hibernate.EhCacheRegionFactory' // Hibernate 3
cache.region.factory_class = 'org.hibernate.cache.ehcache.EhCacheRegionFactory' // Hibernate 4
I copied the applicationContext.xml from the web-app/WEB-INF folder of the new application to the same file of the application I wanted to update.
Then I removed the target folder and tried to run the application by running
> grails run-app.
For one of my applications I got an error after starting. I fixed that application by setting the Hibernate version back from Hibernate 4 to Hibernate 3.