Upgrade from Grails 2.2.2 to 2.4.1

Here’s what was necessary for me to upgrade handful of Grails projects to 2.4.1:

• Change the grails.version in application.properties
• grails clean is your friend when changing dependencies
• change hibernate, tomcat and resources plugin versions to latest
• kick out the spock plugin and the grails-spock dependency as these come now with Grails
• the package of Spock’s IntegrationSpec changed and needs adaptation
• use the applicationContext.xml and web.xml from a fresh 2.4.1 Grails project (be sure to merge in any custom modifications you have)
• some older plugins we use have not been updated to remove use of the deprecated classes ApplicationHolder, PluginManagerHolder, ConfigurationHolder that were completely removed in 2.4 – this can be fixed by copying those removed classes into your project so they are there again
• HTTP method restrictions are also checked in unit tests now, so the correct HTTP method needs to be set in tests
• Anonymous classes caused obscure exceptions (java.lang.NoSuchFieldError this$0, java.lang.VerifyError) in some places – replacing the anonymous class with a closure fixed this problem – this is most likely a Groovy issue
• tripped over a bug in startGrails.bat – on Windows the file.encoding system property was not set anymore (see GRAILS-11534)
• upgrade to 2.4.2 was necessary later because of a bug in JSON serialization GRAILS-11513
• An exception “Cannot create a session after the response has been committed” was fixed by rearranging the code that accessed the session
• needed to adapt some corner case transaction handling code – this is likely caused by the Spring changes introduced by the newer Spring version
• GrailsDomainBinder.getMapping was changed from a static method to instance method – easily fixed by just creating an instance
• Played around with forked execution – we’ll use it for development mode, but not for the tests because of problems with the Geb functional tests
• Support for the old databinding (with grails.databinding.useSpringBinder = true) doesn’t really work in tests
  • In unit tests the old databinding doesn’t work because the setting isn’t picked up – moving the affected tests to integration tests fixes this
  • dateCreated (which we manually set in some tests) isn’t bound by the setProperties databinding anymore – assigning dateCreated manually works as a workaround
  • the old databinding with setProperties doesn’t work for functional tests in some places – when used in Bootstrap.groovy the legacy databinding setting is not picked up – with constructor databinding it works, but not with setProperties
• (change local Grails version and Grails version on CI server)
• somehow when running in production, we needed to add additional dependencies, because missing classes caused ClassNotFoundExceptions. The required dependencies are runtime ‘org.springframework:spring-expression:4.0.5.RELEASE’ and
  runtime ‘org.springframework:spring-aop:4.0.5.RELEASE’

So all in all, the upgrade was not entirely smooth, but all problems could be solved.