This is how I implement the Provider pattern in Groovy.

Providers.groovy

package com.danveloper.providers

import com.danveloper.support.ApplicationHolder as AH
import org.hibernate.SessionFactory as SF

public interface Provider<T> {
  T get()
}

class Support {
  private static def _ = [:]
  public final static def sessionProvider = [get: {
    _.session ?: { _.session = AH.getBean(SF)?.currentSession; _.session }()
  }] as Provider<SF>
}

class ModelDAO extends Support {
  def save(def domainClass) {
    def session = sessionProvider.get()
    def tx = session.beginTransaction()
    def id = session.saveOrUpdate(domainClass)
    tx.commit()
    domainClass
  }
}