Saturday, November 7, 2009

Google App Engine with Grails

After I recently got a grails app to work with spring-security, REST, and cache I wanted to try my luck and create a Google App Engine application using grails. Unfortunately, I think it's still pretty early as I ran into several issues early on. However, I see enormous potential once these issues get resolved.

I am using grails v1.1.1, app-engine plugin v0.8.5, with gorm-jpa v0.5. The first issue I ran into was deploying when using grails app-engine deploy. It failed to work subsequent times after I got the WAR initially deployed using /app-sdk/bin/ It complained about not supplying an email address. Turns out there is a bug related to ant that should get fixed soon. The work around was simple enough; just hit Enter before typing in your email address.

Secondly, I was disappointed to find out that the spring-security (acegi) plugin wasn't compatible in GAE. Based on the compile errors I received locally, it appears spring-security depends on hibernate which is not an option in GAE (you either get JDO or JPA). I chose JPA because according to the documentation, JDO doesn't support any of the GORM dynamic finders methods where as JPA supports most of them. I guess now that I think about it, I'm not suprised acegi didn't work in GAE; just disappointed.

I found a minor issue I submitted concerning the default delete action in generated controllers. Seems the gorm-jpa plugin doesn't wrap the delete method around a [Domain].withTransaction closure which apparently is required (see the save action).

Finally, I was unable to get content negotiation working using the withFormat concept I described here. It worked locally running grails app-engine run, but threw an exception in GAE:

Caused by: access denied java.lang.RuntimePermission getClassLoader

My guess is it's related to the Security issues they report on the FAQ:

"The current preview release of the Google AppEngine SDK has a bug that doesn't allow it to run Groovy code when the full permissions restrictions are used. This will be fixed in the next release, but in the meantime the development environment runs without emulating the permissions restrictions of the actual AppEngine environment."
Overall, I enjoyed the easy commands it provides to build, run, and deploy to GAE. The deploy was suprisingly pretty quick. I was able to view the exceptions in GAE easily. I was just prevented from making any real progress. If you want to see what I did get done, which was not much, check it out here

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