If you are building a grails application, you can use either imageMagick or the imageTools plugin to resize and crop your images. This is not possible in the Google App Engine because it neither allows you install external packages nor whitelists JAI components.
Fortunately, we can use the Java-based image resizing API provided in the App Engine for simple manipulation.
I’ve written about how to write this in Grails, but since the latest update to the App Engine seems to break all my Grails applications ( which is pretty stupid ), I wanted to try to do this in Gaelyk – the lightweight groovy-based framework for the app engine.
You can play with the application here: http://gaelykresize.appspot.com/upload.groovy