Working around the static variable limitations in Groovy scripts

I’ve written a bunch about and used Groovy for examples of various functionality. Still, to this day, coupled with Maven artifact resolution using the Grape subsystem, Groovy is a powerful tool. I end up writing workers, complex scripts that do heavy multithreaded workloads, etc… Often these units of work involve their own classes for some amount of structured data. I recently came across a problem where I was creating entities with various keys and wanted to make sure changes to those keys were represented in the created/update/delete/report methods, so, I began using variables to consistently refer to said keys. Example, from:

def someService = ...

@Canonical
class Person {
  def name

  def insertStatement() {
    "person:${name}"
  }
}

def josh = new Person('josh')

someService.insert('person', josh)

…to:

def someService = ...
def personKey = 'person'

@Canonical
class Person {
  def name

  def insertStatement() {
    "${personKey}:${name}"
  }
}

def josh = new Person('josh')

someService.insert(personKey, josh)

…which of course won’t work because the Person class doesn’t contain personKey, it’s not scoped for the class. No worries, I’ll make it static. Oh wait, groovy scripts can’t use static variable qualifiers. So, instead, leverage this little handy work-around:

def someService = ...

@Singleton class GraphKeys {
  def personNodeType = 'person'
}

@Canonical
class Person {
  def name

  def insertStatement() {
    "${GraphKeys.instance.personKey}:${name}"
  }
}

def josh = new Person('josh')

someService.insert(GraphKeys.instance.personNodeType, josh)

…and voila. We use another class to hold our variables (you could easily have used an Enum with properties/values, too).