HowTo hook into the lift's request processing cycle

From Lift

Lift provides request hook points to invoke your code early before normal request processing. You can use these hook points to log before/after debug messages, capture request start/end times, open/close extra resources, etc.

Usually, you will register these hooks in your bootstrap.liftweb.Boot.boot method.

The S.addAround() API let's you provide your callback function. For example...

 package bootstrap.liftweb
 import net.liftweb.util._
 import net.liftweb.http._
 class Boot {
  def boot { 
    ...
    S.addAround(User.requestLoans) // Z
    S.addAround(List(new LoanWrapper { // Y
      def apply[T](f: => T): T = {
        ...your before code goes here...
        val result = f // Let lift do normal request processing.
        ...your after code goes here...
        result
      }
    }))
    S.addAround(List(new LoanWrapper { // X
      def apply[T](f: => T): T = {
        println("hello to the request!")
        val result = f // Let lift do normal request processing.
        println("goodbye request!")
        result
      }
    }))
    S.addAround(List(around1, around2, around3))
 }

The callbacks will be called in this order: around1, around2, around3, X, Y, Z. That is, logically like...

around1(around2(around3(X(Y(Z(normal request processing)))))