diff --git a/src/main/scala/app/ControllerBase.scala b/src/main/scala/app/ControllerBase.scala
index a8226c6..e6ac526 100644
--- a/src/main/scala/app/ControllerBase.scala
+++ b/src/main/scala/app/ControllerBase.scala
@@ -3,7 +3,7 @@
 import _root_.util.Directory._
 import _root_.util.Implicits._
 import _root_.util.ControlUtil._
-import _root_.util.{FileUtil, Validations}
+import _root_.util.{FileUtil, Validations, Keys}
 import org.scalatra._
 import org.scalatra.json._
 import org.json4s._
@@ -34,7 +34,7 @@
     val path         = httpRequest.getRequestURI.substring(context.length)
 
     if(path.startsWith("/console/")){
-      val account = httpRequest.getSession.getAttribute("LOGIN_ACCOUNT").asInstanceOf[Account]
+      val account = httpRequest.getSession.getAttribute(Keys.Session.LoginAccount).asInstanceOf[Account]
       if(account == null){
         // Redirect to login form
         httpResponse.sendRedirect(context + "/signin?" + path)
@@ -63,7 +63,7 @@
     request.getRequestURI + (if(queryString != null) "?" + queryString else "")
   }
 
-  private def LoginAccount: Option[Account] = session.getAs[Account]("LOGIN_ACCOUNT")
+  private def LoginAccount: Option[Account] = session.getAs[Account](Keys.Session.LoginAccount)
 
   def ajaxGet(path : String)(action : => Any) : Route =
     super.get(path){
@@ -197,14 +197,10 @@
   //  def removeTemporaryFile(fileId: String)(implicit session: HttpSession): Unit =
   //    getTemporaryFile(fileId).delete()
 
-  def removeTemporaryFiles()(implicit session: HttpSession): Unit = FileUtils.deleteDirectory(TemporaryDir)
+  def removeTemporaryFiles()(implicit session: HttpSession): Unit =
+    FileUtils.deleteDirectory(TemporaryDir)
 
   def getUploadedFilename(fileId: String)(implicit session: HttpSession): Option[String] =
-    defining(Option(session.getAttribute("upload_" + fileId).asInstanceOf[String])){ filename =>
-      if(filename.isDefined){
-        session.removeAttribute("upload_" + fileId)
-      }
-      filename
-    }
+    session.getAndRemove[String](Keys.Session.Upload(fileId))
 
 }
\ No newline at end of file
diff --git a/src/main/scala/app/DashboardController.scala b/src/main/scala/app/DashboardController.scala
index 16fa0cb..b8970f1 100644
--- a/src/main/scala/app/DashboardController.scala
+++ b/src/main/scala/app/DashboardController.scala
@@ -1,7 +1,7 @@
 package app
 
 import service._
-import util.UsersAuthenticator
+import util.{UsersAuthenticator, Keys}
 import util.Implicits._
 
 class DashboardController extends DashboardControllerBase
@@ -43,10 +43,9 @@
     import IssuesService._
 
     // condition
-    val sessionKey = "dashboard/issues"
-    val condition = session.putAndGet(sessionKey,
+    val condition = session.putAndGet(Keys.Session.DashboardIssues,
       if(request.hasQueryString) IssueSearchCondition(request)
-      else session.get(sessionKey).getOrElse(IssueSearchCondition()).asInstanceOf[IssueSearchCondition]
+      else session.getAs[IssueSearchCondition](Keys.Session.DashboardIssues).getOrElse(IssueSearchCondition())
     )
 
     val userName = context.loginAccount.get.userName
@@ -75,10 +74,9 @@
     import PullRequestService._
 
     // condition
-    val sessionKey = "dashboard/pulls"
-    val condition = session.putAndGet(sessionKey, {
+    val condition = session.putAndGet(Keys.Session.DashboardPulls, {
       if(request.hasQueryString) IssueSearchCondition(request)
-      else session.getAs[IssueSearchCondition](sessionKey).getOrElse(IssueSearchCondition())
+      else session.getAs[IssueSearchCondition](Keys.Session.DashboardPulls).getOrElse(IssueSearchCondition())
     }.copy(repo = repository))
 
     val userName = context.loginAccount.get.userName
diff --git a/src/main/scala/app/FileUploadController.scala b/src/main/scala/app/FileUploadController.scala
index b788c24..6ea5fa2 100644
--- a/src/main/scala/app/FileUploadController.scala
+++ b/src/main/scala/app/FileUploadController.scala
@@ -1,6 +1,6 @@
 package app
 
-import util.FileUtil
+import _root_.util.{Keys, FileUtil}
 import util.ControlUtil._
 import org.scalatra._
 import org.scalatra.servlet.{MultipartConfig, FileUploadSupport}
@@ -21,7 +21,7 @@
     fileParams.get("file") match {
       case Some(file) if(FileUtil.isImage(file.name)) => defining(generateFileId){ fileId =>
         FileUtils.writeByteArrayToFile(getTemporaryFile(fileId), file.get)
-        session += "upload_" + fileId -> file.name
+        session += Keys.Session.Upload(fileId) -> file.name
         Ok(fileId)
       }
       case None => BadRequest
diff --git a/src/main/scala/app/IssuesController.scala b/src/main/scala/app/IssuesController.scala
index 9adab7c..bff45dd 100644
--- a/src/main/scala/app/IssuesController.scala
+++ b/src/main/scala/app/IssuesController.scala
@@ -4,7 +4,7 @@
 
 import service._
 import IssuesService._
-import util.{CollaboratorsAuthenticator, ReferrerAuthenticator, ReadableUsersAuthenticator, Notifier}
+import util.{CollaboratorsAuthenticator, ReferrerAuthenticator, ReadableUsersAuthenticator, Notifier, Keys}
 import util.Implicits._
 import util.ControlUtil._
 import org.scalatra.Ok
@@ -328,7 +328,7 @@
     defining(repository.owner, repository.name){ case (owner, repoName) =>
       val filterUser = Map(filter -> params.getOrElse("userName", ""))
       val page       = IssueSearchCondition.page(request)
-      val sessionKey = s"${owner}/${repoName}/issues"
+      val sessionKey = Keys.Session.Issues(owner, repoName)
 
       // retrieve search condition
       val condition = session.putAndGet(sessionKey,
diff --git a/src/main/scala/app/PullRequestsController.scala b/src/main/scala/app/PullRequestsController.scala
index 6ee5c34..0d42d92 100644
--- a/src/main/scala/app/PullRequestsController.scala
+++ b/src/main/scala/app/PullRequestsController.scala
@@ -1,6 +1,6 @@
 package app
 
-import util.{LockUtil, CollaboratorsAuthenticator, JGitUtil, ReferrerAuthenticator, Notifier}
+import util.{LockUtil, CollaboratorsAuthenticator, JGitUtil, ReferrerAuthenticator, Notifier, Keys}
 import util.Directory._
 import util.Implicits._
 import util.ControlUtil._
@@ -369,7 +369,7 @@
     defining(repository.owner, repository.name){ case (owner, repoName) =>
       val filterUser = userName.map { x => Map("created_by" -> x) } getOrElse Map("all" -> "")
       val page       = IssueSearchCondition.page(request)
-      val sessionKey = s"${owner}/${repoName}/pulls"
+      val sessionKey = Keys.Session.Pulls(owner, repoName)
 
       // retrieve search condition
       val condition = session.putAndGet(sessionKey,
diff --git a/src/main/scala/app/SignInController.scala b/src/main/scala/app/SignInController.scala
index 79d946e..7d4b2a9 100644
--- a/src/main/scala/app/SignInController.scala
+++ b/src/main/scala/app/SignInController.scala
@@ -3,6 +3,7 @@
 import service._
 import jp.sf.amateras.scalatra.forms._
 import util.Implicits._
+import util.Keys
 
 class SignInController extends SignInControllerBase with SystemSettingsService with AccountService
 
@@ -18,7 +19,7 @@
   get("/signin"){
     val redirect = params.get("redirect")
     if(redirect.isDefined && redirect.get.startsWith("/")){
-      session.setAttribute("REDIRECT", redirect.get)
+      session.setAttribute(Keys.Session.Redirect, redirect.get)
     }
     html.signin(loadSystemSettings())
   }
@@ -39,10 +40,10 @@
    * Set account information into HttpSession and redirect.
    */
   private def signin(account: model.Account) = {
-    session.setAttribute("LOGIN_ACCOUNT", account)
+    session.setAttribute(Keys.Session.LoginAccount, account)
     updateLastLoginDate(account.userName)
 
-    session.getAndRemove[String]("REDIRECT").map { redirectUrl =>
+    session.getAndRemove[String](Keys.Session.Redirect).map { redirectUrl =>
       if(redirectUrl.replaceFirst("/$", "") == request.getContextPath){
         redirect("/")
       } else {
diff --git a/src/main/scala/util/Keys.scala b/src/main/scala/util/Keys.scala
new file mode 100644
index 0000000..9dae8d0
--- /dev/null
+++ b/src/main/scala/util/Keys.scala
@@ -0,0 +1,47 @@
+package util
+
+/**
+ * Define key strings for request attributes, session attributes or flash attributes..
+ */
+object Keys {
+
+  object Session {
+
+    /**
+     * Session key for the logged in account information.
+     */
+    val LoginAccount = "LOGIN_ACCOUNT"
+
+    /**
+     * Session key for the redirect URL.
+     */
+    val Redirect = "REDIRECT"
+
+    /**
+     * Session key for the issue search condition in dashboard.
+     */
+    val DashboardIssues = "dashboard/issues"
+
+    /**
+     * Session key for the pull request search condition in dashboard.
+     */
+    val DashboardPulls = "dashboard/pulls"
+
+    /**
+     * Generate session key for the issue search condition.
+     */
+    def Issues(owner: String, name: String) = s"${owner}/${name}/issues"
+
+    /**
+     * Generate session key for the pull request search condition.
+     */
+    def Pulls(owner: String, name: String) = s"${owner}/${name}/pulls"
+
+    /**
+     * Generate session key for the upload filename.
+     */
+    def Upload(fileId: String) = s"upload_${fileId}"
+
+  }
+
+}