How do you share common methods in different grails controllers?

Question

Currently when I need to share a method like processParams(params) between different controllers, I use either inheritance or services. Both solution has some

Answer 1

You can use the Delegation design pattern:

class Swimmer {
    def swim() { "swimming" }
}

class Runner {
    def run() { "running" }
}

class Biker {
    def bike() { "biking" }
}

class Triathlete { 
    @Delegate Swimmer swimmer
    @Delegate Runner runner
    @Delegate Biker biker
}

def triathlete = new Triathlete(
    swimmer: new Swimmer(),
    runner: new Runner(),
    biker: new Biker()
)

triathlete.swim()
triathlete.run()
triathlete.bike()

In case of a controller, assign the helper class directly at the instance field (or in the nullary constructor):

class HelperClass {
    def renderFoo() { render 'foo' }
}

class FooController {
    private @Delegate HelperClass helperClass = new HelperClass()

    def index = { this.renderFoo() }
}

The delegate's type information gets compiled into the containing class.