Aspect(-like) function for closures - grails

Question

In Grails (at least up to the current version 2.2), taglibs are closures. For certain taglib closures, I'd like to use some "around" type advice / wrap the closure in an interceptor.
To put it another way, let's say there is this taglib straight from the Grails doc:
class SimpleTagLib {
def emoticon = { attrs, body ->
out << body() << (attrs.happy == 'true' ? " :-)" : " :-(")
}
}
Now, without modifying the taglib code, I'd like to time how long "emoticon" takes to execute.
Spring AOP (and all other AOP I can find) only seems to work on Java methods - and taglibs are always based on closures. An "around" pointcut would be perfect for this, but I can't figure out how to make it work.

Answer 1

I've written something similar which I put as a public closure in a category I then mixin to services:
// TimingCategory.groovy
/**
* Provides common AOP timing functionality to Services which mixin this category.
*/
class TimingCategory {
static Closure timer = { String label = "The call", Closure closure ->
Long start = System.currentTimeMillis()
def result = closure.call()
Long end = System.currentTimeMillis()
Long duration = end - start
log.warn "${label} took ${duration} ms"
return result
}
}
In other classes, you just reference the timer closure as such:
#Mixin(TimingCategory)
public class WhateverService {
public String doSomeWork() {
timer "Doing a lot of work", {
1000.times { doSomething() }
someMethodWithAStringReturnValue()
}
}
}
That will give you log output of "WARN: Doing a lot of work took nn ms" and return the value of the inner closure as the return value of the doSomeWork method.
For your taglib instance, just wrap the out << ... in the
timer "Writing an emoticon", {
// your code
}
code.
If you don't care about passing through the internal return value, you could instead return the duration as the result of the closure invocation.
Update:
I might have misread -- you're asking how to wrap the taglib execution without modifying the taglib code at all? What about creating a custom taglib which accepts the body and passes it to the other taglibs for execution?
I haven't tried this, but something like:
class TimedTagLib {
static namespace = "timer"
def timedTag = { attrs, body ->
timer "Executing the timed tag", {
out << body()
}
}
}
And invoking it like
<timer:timedTag><g:emoticon whatever="something">Text</g:emoticon></timer:timedTag>
Update 2:
Ok, so I tried it. Works fine. My final code (I added a second timer closure which returns the duration):
// TimedTagLib.groovy
#Mixin(TimingCategory)
class TimedTagLib {
static namespace = "timer"
def timedTag = { attrs, body ->
def duration = returnTimer "Printing the timed tag", {
out << body()
}
out << "Took ${duration} ms to print"
}
}
And the view:
// someView.gsp
<timer:timedTag>
<g:formatLocalDate date="${LocalDate.now()}" />
</timer:timedTag>
The resulting HTML is:
03/19/2013
Took 6 ms to print
And it also wrote to the log.