Grails: adding dynamic methods within a plugin

Question

Hi,

I'm developing a plugin that adds a getFlashHelper method to each controller. This method should return an instance of a FlashHelper class.

However, the constructor of the FlashHelper class must be passed the instance of the controller on which the getFlashHelper method was called.

Hopefully the following code will explain what I'm doing a bit better

def doWithDynamicMethods = {ctx ->

    application.controllerClasses*.metaClass*.getFlashHelper = {

        def controllerInstance = delegate

        // Avoid creating a new FlashHelper each time the 'flashHelper' property is accessed
        if (!controllerInstance.metaClass.hasProperty('flashHelperInstance')) {
            controllerInstance.metaClass.flashHelperInstance = new FlashHelper(controller: controllerInstance)
        }

        // Return the FlashHelper instance. There may be a simpler way, but I tried
        // controllerInstance.metaClass.getMetaProperty('flashHelperInstance')
        // and it didn't work
        return controllerInstance.metaClass.getMetaProperty('flashHelperInstance').getter.invoke(controllerInstance, [] as Object[])
    }
}

The code appears to work, but I can't help feeling that there must be an easier way of doing this. That last line is particularly gruesome. Is there any way I can simplify this?

Thanks, Don

Answer 1

Since controllers are created per-request, I'd store the helper as a Request attribute:

for (c in grailsApplication.controllerClasses) {
   c.clazz.metaClass.getFlashHelper = { ->
      def controllerInstance = delegate
      def request = controllerInstance.request
      def helper = request['__flash_helper__']
      if (!helper) {
         helper = new FlashHelper(controller: controllerInstance)
         request['__flash_helper__'] = helper
      }
      helper
   }
}