Programming with closures

Recently I caught myself thinking that my programming habits are changing while programming in Groovy. In particular, I started using closures more and more to clean up my code, make it more DRYer, e.g. by not just merely using existing closures provided by libraries such as GDK, GORM, etc., but by creating my own closures.

Here's a small example from GrailsCrowd. The idea here is to either 'accept project participation invitation' or 'reject project participation invitation'. So, in the Controller, I factored out the common code of retrieving the Member, Project, redirecting to the appropriate action afterwards, etc. to a private method which takes a closure, and calling that closure for the actual action of 'acceptance' or 'rejection':

private def withProject(callable) {
    def invitee = freshCurrentlyLoggedInMember()
    def creator = Member.findByName(params.creator)
    def project = GrailsProject.get(params.projectId)
    //Call the closure
    callable([project:project,creator:creator,invitee:invitee])
    redirect(controller: 'mailbox')
}

def acceptParticipationInvitation = {
    withProject {projectMap ->
        projectMap.project.acknowlegeParticipationAcceptance(projectMap.creator, 
        projectMap.invitee, params.messageId.toLong())
    }
}

def rejectParticipationInvitation = {
    withProject {projectMap ->
        projectMap.project.rejectParticipationInvitation(projectMap.creator, 
        projectMap.invitee, params.messageId.toLong())
    }
}

IMO, this makes code cleaner, reusable, and more maintainable. Also, this style of programming with closures kind of replaces good old Template Method design pattern.

Keep on Groovying, folks!

Later...

Hidden gem: grails.war.resources

In the process of packaging up the Grails application as a WAR in preparation for deployment to Tomcat, I needed to figure out a way to exclude the Oracle JDBC drver from WEB-INF/lib (we use 'shared' Oracle driver for our web apps which gets loaded by the Catalina's common ClassLoader). So I was thinking of a way to provide an "event hook" script, and while reading Grails' War.groovy I found a "hidden gem". That is a closure which is defined in the application's Config.groovy. So when this closure is defined, the War.groovy calls it with "staging directory" as a parameter and sets Ant as its 'delegate' right before zipping it up as a war.

So I was able to do the following (... from Config.groovy):

//Closure to customize the packaging of a war. In particular it excludes the Oracle JDBC driver
//from the war as it is loaded by the Catalina common ClassLoader when deployed to Tomcat
grails.war.resources = {stagingDir ->
 delete(file: "$stagingDir/WEB-INF/lib/ojdbc14-10.2.jar")
}

This is real nice, but I don't think this feature is documented anywhere.

Later...