Scala lift : Access Session Information In Actors.

Problem: In Scala Lift Application. There are two ways to maintain and access the session information. Either we can use SessionVars or net.liftweb.http.S object. Each of them work significantly well until there are used in the scope of session.

Now the actual problem arise when I used Actor to get concurrency in scala lift application. Actor runs outside of the context of the session that you set the SessionVar or S object.I used scala Actor, Akka Actor, Lift Actor but no one is able to hold the session state.

In the context of session it is quite possible to get the locale using S.get(“locale”) throughout the application.

But I use Actor, It is not possible for Actor to maintain the session. so It is not possible to get locale from Session or S Object.

When you hit the Actor with the message “Hello”. MyActor shoud print ” Hello in it_IT “.
But unfortunately you are not so lucky. It prints “Hello in” instead of “Hello in it_IT”. This problem arise because Actor breaks the context of session so MyActor is not able to retrieve the Session information.

Solution : Fortunatly lift has initIfUninitted for rescue. It initialize the current request session if it’s not already initialized. Generally this is handled by Lift during request processing, but this method is available in case you want to use S outside the scope of a request (standard HTTP , Comet and Actor).

Now Every thing will work fine. By using S.initIfUninitted you can initialize the session object explicitly in the Actor.

Written by 

Mayank is a polyglot programmer who believes in selecting the right tool for the job. He has more than 8-year experience in Java Platform. He has been a Scala enthusiast ever since he came to know this beautiful language in 2010. He has been developing enterprise applications on the reactive stack. He's a big fan of agile development, scalable software and elegant code. Mayank has extensive knowledge in a huge spectrum of areas of software, and the ability to dive deeply into a new technology and achieve expert level in no-time. He found fun to architect complex systems in the simplest way and quite handy in Design patterns, micro-services & DevOps technologies. On the personal front, he is a marathon runner, spiritual learner & yoga practitioner.

2 thoughts on “Scala lift : Access Session Information In Actors.

  1. Hi 🙂 I’m having some trouble getting your example to work. Can you please assist? My code below:

    object SetLocale{

    S.set(“locale”,”it”)

    }

    object CallTheActor {

    def render = SHtml.onSubmit(x => {
    MyActor ! (x, S.session) //This is the problem, method “def session” in S is of type Box[LiftSession] please see the API
    SetValById(“clearcontents”, “”)
    })
    }

    object MyActor extends LiftActor {

    def messageHandler = {

    case (msg, s:LiftSession) => S.initIfUninitted(s) { //Doesn’t match because “S.session” is Box[LiftSession]
    println(msg +”In “+S.get(“locale”).openOr(“”))
    }

    /*

    //If you add the case below you get a compiler error saying:
    //found : net.liftweb.common.Box[net.liftweb.http.LiftSession]
    //required: net.liftweb.http.LiftSession
    //Check out S in the API you will see there is no method in S to simply call LiftSession, only method “def session” to call Box[LiftSession]
    //Method initIfUninitted is S requires type LfitSession and not Box[LiftSession]
    //So how do you give LiftSession to S.initIfUninitted(??) ?

    case (msg, s:Box[LiftSession]) => S.initIfUninitted(s) {
    println(msg +”In “+S.get(“locale”).openOr(“”))

    }

    }
    */

    }

    1. Hi Tylor,
      This is a good catch. Thanks for finding the Typo.
      >>MyActor ! (x, S.session) //This is the problem, method “def session” in S is of type Box[LiftSession] please see the API

      But the actual call should be like this
      MyActor ! (x, S.session.open_!) // Now this statement will hit the Actor with the LiftSession, instead of Box[LiftSession]

      I hope, now this would work as expected.

      Thank You!

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