liftweb - accessing get/post parameters

Question

How is it possible to simply access to get and post attributes in lift framework inside RestHelper? There are no any explicit examples about it in documentation :(

package my.domain

import net.liftweb.http._
import net.liftweb.http.rest._
import net.liftweb.json.JsonAST._
import net.liftweb.json._
import net.liftweb.common.{Box,Full,Empty,Failure,ParamFailure}
import net.liftweb.mapper._


import ru.dmteam.model.{RssItem}

object ContentRest extends RestHelper {


    def getq: String = {
        val q = S.param("q")
        q.toString
    }

    serve {
        case "api" :: "static" :: _ XmlGet _=> <b>{getq}</b>

    }
}

I want to understand how to make lift show value of q when I am requesting http://localhost:8080/api/static.xml?q=test

Answer 1

Lift uses Box rather than null to indicate if a parameter was passed. This allows the nice use of Scala's for comprehension to chain together a nice request handler. I'll let the code speak for itself:

object MyRest extends RestHelper {
  // serve the q parameter if it exists, otherwise
  // a 404
  serve {
    case "api" :: "x1" :: _ Get _ =>
      for {
        q <- S.param("q")
      } yield <x>{q}</x>
  }

  // serve the q parameter if it exists, otherwise
  // a 404 with an error string
  serve {
    case "api" :: "x2" :: _ Get _ =>
      for {
        q <- S.param("q") ?~ "Param 'q' missing"
      } yield <x>{q}</x>
  }

  // serve the q parameter if it exists, otherwise
  // a 401 with an error string
  serve {
    case "api" :: "x2" :: _ Get _ =>
      for {
        q <- S.param("q") ?~ "Param 'q' missing" ~> 401
      } yield <x>{q}</x>
  }

  // serve the q, r, s parameters if this exists, otherwise
  // different errors
  serve {
    case "api" :: "x3" :: _ Get _ =>
      for {
        q <- S.param("q") ?~ "Param 'q' missing" ~> 401
        r <- S.param("r") ?~ "No 'r'" ~> 502
        s <- S.param("s") ?~ "You're s-less" ~> 404
      } yield <x><q>{q}</q><r>{r}</r><s>{s}</s></x>
  }

}