Lift Framework example source code file (Vars.scala)

This example Lift Framework source code file (Vars.scala) is included in the DevDaily.com "Java Source Code Warehouse" project. The intent of this project is to help you "Learn Java by Example" ^TM.

Java - Lift Framework tags/keywords

boolean, box, containerserializer, containerserializer, full, requestvar, sessionvar, string, string, t, t, threadglobal, threading, threads, unit, unit

The Lift Framework Vars.scala source code

/*
 * Copyright 2007-2011 WorldWide Conferencing, LLC
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *     http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

package net.liftweb
package http

import net.liftweb.common._
import net.liftweb.util._
import Helpers._
import scala.collection.mutable.{HashMap, HashSet, ListBuffer}
import java.util.concurrent.Callable

/**
 * The bridge between Scala *Vars implementations and
 * the 
 */
class VarsJBridge {
  def vendSessionVar[T](default: T, e: Exception): SessionVar[T] = {
    vendSessionVar(new Callable[T] {
      def call() = default
    }, e)
  }

  def vendSessionVar[T](default: Callable[T], e: Exception): SessionVar[T] = {
    new SessionVar(default.call()) {
      override val __nameSalt = e.getStackTrace.apply(1).toString
    }
  }
}

/**
 * A typesafe container for data with a lifetime nominally equivalent to the
 * lifetime of HttpSession attributes.
 *
 * <code>
 * object MySnippetCompanion {
 *   object mySessionVar extends SessionVar[String]("hello")
 * }
 * </code>
 *
 * The standard pattern is to create a singleton object extending SessionVar instead
 * of creating an instance variable of a concrete SessionVar subclass. This is preferred
 * because SessionVar will use the name of its instantiating class for part of its state
 * maintenance mechanism.
 *
 * If you find it necessary to create a SessionVar subclass of which there may be more
 * than one instance, it is necessary to override the __nameSalt() method to return
 * a unique salt value for each instance to prevent name collisions.
 *
 * Note: SessionVars can be used within CometActors
 *
 * @param dflt - the default value to be returned if none was set prior to
 * requesting a value to be returned from the container
 */
abstract class SessionVar[T](dflt: => T) extends AnyVar[T, SessionVar[T]](dflt) with LazyLoggable {
  override protected def findFunc(name: String): Box[T] = S.session match {
    case Full(s) => s.get(name)
    case _ =>
      if (LiftRules.throwOnOutOfScopeVarAccess) {
        throw new IllegalAccessException("Access to SessionVar outside a request or comet actor scope")
      }

      if (showWarningWhenAccessedOutOfSessionScope_?)
        logger.warn("Getting a SessionVar " + name + " outside session scope") // added warning per issue 188

      Empty
  }

  /**
   * Stateless session enforcement is new to Lift, but there
   * are some legacy issues in WebKit and allowing for a SessionVar
   * to be "magic" (settable even in stateless sessions) seems to be
   * an efficient, yet somewhat hacky, way around the issue
   */
  private[liftweb] def magicSessionVar_? = false

  override protected def setFunc(name: String, value: T): Unit = S.session match {
    // If we're in a stateless session, don't allow SessionVar setting
    case Full(s) if !magicSessionVar_? && !s.stateful_? && !settingDefault_? =>
      throw new StateInStatelessException("setting a SessionVar in a " +
        "stateless session: " + getClass.getName)

    case Full(s) => s.set(name, value)
    case _ =>
      if (LiftRules.throwOnOutOfScopeVarAccess) {
        throw new IllegalAccessException("Access to SessionVar outside a request or comet actor scope")
      }

      if (showWarningWhenAccessedOutOfSessionScope_?)
        logger.warn("Setting a SessionVar " + name + " to " + value + " outside session scope") // added warning per issue 188
  }

  /**
   * Different Vars require different mechanisms for synchronization.  This method implements
   * the Var specific synchronization mechanism
   */
  def doSync[F](f: => F): F = S.session match {
    case Full(s) =>
      // lock the session while the Var-specific lock object is found/created
      val lockName = name + VarConstants.lockSuffix
      val lockObj = s.synchronized {
        s.get[AnyRef](lockName) match {
          case Full(lock) => lock
          case _ => val lock = new AnyRef
          s.set(lockName, lock)
          lock
        }
      }

      // execute the query in the scope of the lock obj
      lockObj.synchronized {
        f
      }
    case _ => f
  }

  def showWarningWhenAccessedOutOfSessionScope_? = false

  override protected def clearFunc(name: String): Unit = S.session.foreach(_.unset(name))

  override protected def wasInitialized(name: String): Boolean = {
    val bn = name + VarConstants.initedSuffix
    val old: Boolean = S.session.flatMap(_.get(bn)) openOr false
    S.session.foreach(_.set(bn, true))
    old
  }

  override protected def testWasSet(name: String): Boolean = {
    val bn = name + VarConstants.initedSuffix
    S.session.flatMap(_.get(name)).isDefined || (S.session.flatMap(_.get(bn)) openOr false)
  }

  protected override def registerCleanupFunc(in: LiftSession => Unit): Unit =
    S.session.foreach(_.addSessionCleanup(in))

  type CleanUpParam = LiftSession
}

private[http] trait HasLogUnreadVal {
  def logUnreadVal: Boolean
}


/**
 * A typesafe container for data with a lifetime nominally equivalent to the
 * lifetime of HttpSession attributes.  This alternative to SessionVar
 * keeps data in the container's session and must be serializable to
 * support session migration.  Use SessionVars unless you are using
 * MigratoryLiftSessions.
 *
 * <code>
 * object MySnippetCompanion {
 *   object mySessionVar extends ContainerVar[String]("hello")
 * }
 * </code>
 *
 * The standard pattern is to create a singleton object extending ContainerVar instead
 * of creating an instance variable of a concrete ContainerVar subclass. This is preferred
 * because ContainerVar will use the name of its instantiating class for part of its state
 * maintenance mechanism.
 *
 * If you find it necessary to create a ContainerVar subclass of which there may be more
 * than one instance, it is necessary to override the __nameSalt() method to return
 * a unique salt value for each instance to prevent name collisions.
 *
 * @param dflt - the default value to be returned if none was set prior to
 * requesting a value to be returned from the container
 * @param containerSerializer -- an implicit parameter that keeps us honest
 * about only storing things that can be actually serialized.  Lift
 * provides a subset of these.
 */
abstract class ContainerVar[T](dflt: => T)(implicit containerSerializer: ContainerSerializer[T]) extends AnyVar[T, ContainerVar[T]](dflt) with LazyLoggable {
  override protected def findFunc(name: String): Box[T] = S.session match {
    case Full(session) => {
      localGet(session, name) match {
        case Full(array: Array[Byte]) => Full(containerSerializer.deserialize(array))
        case _ => Empty
      }
    }

    case _ => {
      if (showWarningWhenAccessedOutOfSessionScope_?)
        logger.warn("Getting a SessionVar " + name + " outside session scope") // added warning per issue 188

      Empty
    }
  }

  private def localSet(session: LiftSession, name: String, value: Any): Unit = {
    for {
      httpSession <- session.httpSession
    } httpSession.setAttribute(name, value)
  }

  private def localGet(session: LiftSession, name: String): Box[Any] = {
    for {
      httpSession <- session.httpSession
      attr <- Box !! httpSession.attribute(name)
    } yield attr
  }


  override protected def setFunc(name: String, value: T): Unit = S.session match {
    // If we're in a stateless session, don't allow SessionVar setting
    case Full(s) if !s.allowContainerState_? && !s.stateful_? && !settingDefault_? =>
      throw new StateInStatelessException("setting a SessionVar in a " +
        "stateless session: " + getClass.getName)

    case Full(session) => {
      localSet(session, name, containerSerializer.serialize(value))
    }

    case _ =>
      if (showWarningWhenAccessedOutOfSessionScope_?)
        logger.warn("Setting a ContainerVar " + name + " to " + value + " outside session scope") // added warning per issue 188
  }

  /**
   * Different Vars require different mechanisms for synchronization.  This method implements
   * the Var specific synchronization mechanism.
   *
   * In the case of ContainerVar, we synchronize on the ContainerVar
   * instance itself.
   */
  def doSync[F](f: => F): F = this.synchronized(f)

  def showWarningWhenAccessedOutOfSessionScope_? = false

  override protected def clearFunc(name: String): Unit =
    for {
      session <- S.session
      httpSession <- session.httpSession
    } httpSession.removeAttribute(name)

  override protected def wasInitialized(name: String): Boolean = {
    val bn = name + VarConstants.initedSuffix
    val old: Boolean = S.session.flatMap(s => localGet(s, bn) match {
      case Full(b: Boolean) => Full(b)
      case _ => Empty
    }) openOr false
    S.session.foreach(s => localSet(s, bn, true))
    old
  }

  override protected def testWasSet(name: String): Boolean = {
    val bn = name + VarConstants.initedSuffix
    S.session.flatMap(s => localGet(s, name)).isDefined ||
      (S.session.flatMap(s => localGet(s, bn) match {
        case Full(b: Boolean) => Full(b)
        case _ => Empty
      }) openOr false)
  }

  protected override def registerCleanupFunc(in: LiftSession => Unit): Unit =
    S.session.foreach(_.addSessionCleanup(in))

  type CleanUpParam = LiftSession
}

/**
 * A trait that provides *actual* serialization of a type so that
 * the type can be stored into a container's session and be migrated across
 * servers
 */
trait ContainerSerializer[T] {
  def serialize(in: T): Array[Byte]

  def deserialize(in: Array[Byte]): T
}

object ContainerSerializer {

  import java.util.Date
  import org.joda.time.DateTime

  private def buildSerializer[T]: ContainerSerializer[T] =
    new ContainerSerializer[T] {

      import java.io._

      def serialize(in: T): Array[Byte] = {
        val bos = new ByteArrayOutputStream()
        val oos = new ObjectOutputStream(bos)
        oos.writeObject(in)
        oos.flush()
        bos.toByteArray()
      }

      def deserialize(in: Array[Byte]): T = {
        val bis = new ByteArrayInputStream(in)
        val ois = new ObjectInputStream(bis)
        ois.readObject.asInstanceOf[T]
      }
    }

  implicit val objectSerializer: ContainerSerializer[Object] = buildSerializer
  implicit val intSerializer: ContainerSerializer[Int] = buildSerializer
  implicit val longSerializer: ContainerSerializer[Long] = buildSerializer
  implicit val charSerializer: ContainerSerializer[Char] = buildSerializer
  implicit val shortSerializer: ContainerSerializer[Short] = buildSerializer
  implicit val byteSerializer: ContainerSerializer[Byte] = buildSerializer
  implicit val floatSerializer: ContainerSerializer[Float] = buildSerializer
  implicit val doubleSerializer: ContainerSerializer[Double] = buildSerializer
  implicit val booleanSerializer: ContainerSerializer[Boolean] = buildSerializer
  implicit val dateSerializer: ContainerSerializer[Date] = buildSerializer
  implicit val stringSerializer: ContainerSerializer[String] = buildSerializer
  implicit val jodaDateSerializer: ContainerSerializer[DateTime] = buildSerializer

  implicit def arraySerializer[T](implicit tc: ContainerSerializer[T]): ContainerSerializer[Array[T]] = buildSerializer

  implicit def listSerializer[T](implicit tc: ContainerSerializer[T]): ContainerSerializer[List[T]] = buildSerializer

}

/**
 * Create case objects that implement this trait and use the case objects to denote
 * specific SnapshotGroups for RequestVars
 */
trait RequestVarSnapshotGroup

/**
 * This subclass of RequestVars that allow the specification of a RequestVarSnapshotGroup.
 * You can create a snapshot of all the members of this group in RequestVar.snapshot
 */
abstract class SnapshotRequestVar[T](val group: RequestVarSnapshotGroup, d: => T) extends RequestVar[T](d) {

  /**
   * The Snapshot group this requestvar is part of
   */
  override def snapshotGroup: Box[RequestVarSnapshotGroup] = Full(group)
}

/**
 * The companion object to RequestVars
 */
object RequestVar {
  /**
   * Given a RequestVarSnapshotGroup, generate a function that will snapshot all the RequestVars in
   * that group.  When the function is run, the RequestVars will be set to the value they held
   * when they were snapshotted
   */
  def snapshot(group: RequestVarSnapshotGroup): () => Unit = {
    // capture the restore functions
    val funcs = RequestVarHandler.instancesOfGroup(group).map(_.snapshot())

    // return a function that applies all the restore functions
    () => funcs.foreach(_.apply())
  }
}

/**
 * A typesafe container for data with a lifetime nominally equivalent to the
 * lifetime of a page rendered by an HTTP request.
 * RequestVars maintain their value throughout the duration of the current HTTP
 * request and any callbacks for servicing AJAX calls associated with the rendered page.
 * RequestVar instances have no value at the beginning of request servicing (excluding
 * AJAX callbacks) and their value is discarded at the end of request processing.
 * They are commonly used to share values across many snippets. Basic usage:
 *
 * <code>
 * object MySnippetCompanion {
 *   object myRequestVar extends RequestVar[String]("hello")
 * }
 * </code>
 *
 * The standard pattern is to create a singleton object extending RequestVar instead
 * of creating an instance variable of a concrete RequestVar subclass. This is preferred
 * because RequestVar will use the name of its instantiating class for part of its state
 * maintenance mechanism.
 *
 * If you find it necessary to create a RequestVar subclass of which there may be more
 * than one instance, it is necessary to override the __nameSalt() method to return
 * a unique salt value for each instance to prevent name collisions.
 *
 * @param dflt - the default value to be returned if none was set prior to
 * requesting a value to be returned from the container
 */
abstract class RequestVar[T](dflt: => T) extends AnyVar[T, RequestVar[T]](dflt) with HasLogUnreadVal {
  type CleanUpParam = Box[LiftSession]

  /**
   * Is this RequestVar a member of a snapshot group?  If so, specify the group here
   */
  def snapshotGroup: Box[RequestVarSnapshotGroup] = Empty

  /**
   * Return a function that, when applied, will set the value of the RequestVar to its
   * current value
   */
  def snapshot(): () => Unit = {
    if (set_?) {
      val v = this.get
      () => this.set(v)
    } else {
      () => this.remove()
    }
  }

  override protected def findFunc(name: String): Box[T] = RequestVarHandler.get(name)

  override protected def setFunc(name: String, value: T): Unit = RequestVarHandler.set(name, this, value)

  override protected def clearFunc(name: String): Unit = RequestVarHandler.clear(name)

  override protected def wasInitialized(name: String): Boolean = {
    val bn = name + VarConstants.initedSuffix
    val old: Boolean = RequestVarHandler.get(bn) openOr false
    RequestVarHandler.set(bn, this, true)
    old
  }

  /**
   * Different Vars require different mechanisms for synchronization.  This method implements
   * the Var specific synchronization mechanism
   */
  def doSync[F](f: => F): F = f

  // no sync necessary for RequestVars... always on the same thread

  override protected def testWasSet(name: String): Boolean = {
    val bn = name + VarConstants.initedSuffix
    RequestVarHandler.get(name).isDefined || (RequestVarHandler.get(bn) openOr false)
  }

  /**
   * Generate a function that will take a snapshot of the current RequestVars
   * such that they can be restored
   */
  final def generateSnapshotRestorer[T](): Function1[Function0[T], T] = RequestVarHandler.generateSnapshotRestorer()

  override protected def registerCleanupFunc(in: Box[LiftSession] => Unit): Unit = {
    RequestVarHandler.addCleanupFunc(in)
  }

  /**
   * This defines whether or not Lift will log when a RequestVar is set but then not read within
   * the same request cycle. Change this to false to turn off logging. Logging can also be turned
   * off globally via LiftRules.logUnreadRequestVars.
   *
   * @see LiftRules#logUnreadRequestVars
   */
  def logUnreadVal = true
}

/**
 * A typesafe container for data with a lifetime strictly equal to the processing of a single
 * HTTP request. Unlike ordinary RequestVar instances, TransientRequestVars will not maintain
 * data for servicing of AJAX callbacks from a rendered page. This is useful in cases where
 * the value stored within the RequestVar cannot safely be used across multiple requests; an
 * example of such a value is a JTA UserTransaction which has a lifecycle strictly coupled
 * to the actul HTTP request handling by the enclosing container.
 *
 * @param dflt - the default value to be returned if none was set prior to
 * requesting a value to be returned from the container
 */
abstract class TransientRequestVar[T](dflt: => T) extends AnyVar[T, TransientRequestVar[T]](dflt) with HasLogUnreadVal {
  type CleanUpParam = Box[LiftSession]

  override protected def findFunc(name: String): Box[T] = TransientRequestVarHandler.get(name)

  override protected def setFunc(name: String, value: T): Unit = TransientRequestVarHandler.set(name, this, value)

  override protected def clearFunc(name: String): Unit = TransientRequestVarHandler.clear(name)

  override protected def wasInitialized(name: String): Boolean = {
    val bn = name + VarConstants.initedSuffix
    val old: Boolean = TransientRequestVarHandler.get(bn) openOr false
    TransientRequestVarHandler.set(bn, this, true)
    old
  }

  protected override def testWasSet(name: String): Boolean = {
    val bn = name + VarConstants.initedSuffix
    TransientRequestVarHandler.get(name).isDefined || (TransientRequestVarHandler.get(bn) openOr false)
  }

  /**
   * Different Vars require different mechanisms for synchronization.  This method implements
   * the Var specific synchronization mechanism
   */
  def doSync[F](f: => F): F = f

  // no sync necessary for RequestVars... always on the same thread

  override protected def registerCleanupFunc(in: Box[LiftSession] => Unit): Unit =
    TransientRequestVarHandler.addCleanupFunc(in)

  /**
   * This defines whether or not Lift will log when a RequestVar is set but then not read within
   * the same request cycle. Change this to false to turn off logging. Logging can also be turned
   * off globally via LiftRules.logUnreadRequestVars.
   *
   * @see LiftRules#logUnreadRequestVars
   */
  def logUnreadVal = false
}

trait CleanRequestVarOnSessionTransition {
  self: RequestVar[_] =>
}

private[http] object RequestVarHandler extends CoreRequestVarHandler {
  type MyType = RequestVar[_]


  private[http] def instancesOfGroup(grp: RequestVarSnapshotGroup): List[MyType] = {
    val cmp = Full(grp)
    for {
      bs <- backingStore.toList
      (rv, _, _) <- bs.values if rv.snapshotGroup == cmp
    } yield rv
  }
}

private[http] object TransientRequestVarHandler extends CoreRequestVarHandler {
  type MyType = TransientRequestVar[_]
}

private[http] trait CoreRequestVarHandler {
  type MyType <: HasLogUnreadVal

  private val logger = Logger(classOf[CoreRequestVarHandler])
  // This maps from the RV name to (RV instance, value, set-but-not-read flag)
  private val vals: ThreadGlobal[HashMap[String, (MyType, Any, Boolean)]] = new ThreadGlobal
  private val cleanup: ThreadGlobal[ListBuffer[Box[LiftSession] => Unit]] = new ThreadGlobal
  private val isIn: ThreadGlobal[String] = new ThreadGlobal
  private val sessionThing: ThreadGlobal[Box[LiftSession]] = new ThreadGlobal

  /**
   * Generate a function that will take a snapshot of the current RequestVars
   * such that they can be restored
   */
  final def generateSnapshotRestorer[T](): Function1[Function0[T], T] = {
    val myVals = vals.value
    val mySessionThing = sessionThing.value

    f => isIn.doWith("in")(
      vals.doWith(myVals)(
        cleanup.doWith(new ListBuffer) {
          sessionThing.doWith(mySessionThing) {
            val ret: T = f()

            cleanup.value.toList.foreach(clean => Helpers.tryo(clean(sessionThing.value)))

            ret
          }
        }
      )
    )
  }

  protected def backingStore: Box[HashMap[String, (MyType, Any, Boolean)]] =
    vals.value match {
      case null =>
        if (LiftRules.throwOnOutOfScopeVarAccess) {
          throw new IllegalAccessException("Access to Var outside a request or comet actor scope")
        }
        None
      case x => Full(x)
    }

  private[http] def get[T](name: String): Box[T] =
    for {
      ht <- backingStore
      (rvInstance, value, unread) <- ht.get(name)
    } yield {
      if (unread) {
        // Flag the variable as no longer being set-but-unread
        ht(name) = (rvInstance: MyType, value.asInstanceOf[T], false)
      }
      value.asInstanceOf[T]
    }

  private[http] def set[T](name: String, from: MyType, value: T): Unit =
    for (ht <- backingStore)
      ht(name) = (from, value, true)

  private[http] def clear(name: String): Unit =
    for (ht <- backingStore)
      ht -= name

  private[http] def addCleanupFunc(f: Box[LiftSession] => Unit): Unit =
    for (cu <- Box.legacyNullTest(cleanup.value))
      cu += f

  def apply[T](session: Box[LiftSession], f: => T): T = {
    if ("in" == isIn.value) {
      val tv = vals.value

      // remove all the session variables that are CleanRequestVarOnSessionTransition
      val toRemove: Iterable[String] = tv.flatMap {
        case (name, (it: CleanRequestVarOnSessionTransition, _, _)) => List(name)
        case _ => Nil
      }

      toRemove.foreach(n => tv -= n)


      sessionThing.set(session)
      f
    } else {
      isIn.doWith("in")(
        vals.doWith(new HashMap)(
          cleanup.doWith(new ListBuffer) {
            sessionThing.doWith(session) {
              val ret: T = f

              cleanup.value.toList.foreach(clean => Helpers.tryo(clean(sessionThing.value)))

              if (Props.devMode && LiftRules.logUnreadRequestVars) {
                vals.value.keys.filter(!_.startsWith(VarConstants.varPrefix + "net.liftweb"))
                  .filter(!_.endsWith(VarConstants.initedSuffix))
                  .foreach(key => vals.value(key) match {
                  case (rv, _, true) if rv.logUnreadVal => logger.warn("RequestVar %s was set but not read".format(key.replace(VarConstants.varPrefix, "")))
                  case _ =>
                })
              }

              ret
            }
          }
        )
      )
    }
  }
}


object AnyVar {
  implicit def whatSessionVarIs[T](in: SessionVar[T]): T = in.is

  implicit def whatRequestVarIs[T](in: RequestVar[T]): T = in.is

  implicit def whatTransientRequestVarIs[T](in: TransientRequestVar[T]): T = in.is
}

/**
 * Memoize a value for the duration of the user's session
 */
abstract class SessionMemoize[K, V] extends MemoizeVar[K, V] {

  protected object coreVar extends SessionVar[LRU[K, Box[V]]](buildLRU) {
    override def __nameSalt = SessionMemoize.this.__nameSalt
  }

}

/**
 * Memoize a value for the duration of the current request (and subsequent Ajax requests made as a result of viewing the page)
 */
abstract class RequestMemoize[K, V] extends MemoizeVar[K, V] {

  protected object coreVar extends RequestVar[LRU[K, Box[V]]](buildLRU) {
    override def __nameSalt = RequestMemoize.this.__nameSalt
  }

}

/**
 * Memoize a value for the duration of the current HTTP request
 */
abstract class TransientRequestMemoize[K, V] extends MemoizeVar[K, V] {

  protected object coreVar extends TransientRequestVar[LRU[K, Box[V]]](buildLRU) {
    override def __nameSalt = TransientRequestMemoize.this.__nameSalt
  }

}