diff --git a/src/main/scala/app/ControllerBase.scala b/src/main/scala/app/ControllerBase.scala
index e6ac526..a3406cc 100644
--- a/src/main/scala/app/ControllerBase.scala
+++ b/src/main/scala/app/ControllerBase.scala
@@ -67,37 +67,37 @@
 
   def ajaxGet(path : String)(action : => Any) : Route =
     super.get(path){
-      request.setAttribute("AJAX", "true")
+      request.setAttribute(Keys.Request.Ajax, "true")
       action
     }
 
   override def ajaxGet[T](path : String, form : MappingValueType[T])(action : T => Any) : Route =
     super.ajaxGet(path, form){ form =>
-      request.setAttribute("AJAX", "true")
+      request.setAttribute(Keys.Request.Ajax, "true")
       action(form)
     }
 
   def ajaxPost(path : String)(action : => Any) : Route =
     super.post(path){
-      request.setAttribute("AJAX", "true")
+      request.setAttribute(Keys.Request.Ajax, "true")
       action
     }
 
   override def ajaxPost[T](path : String, form : MappingValueType[T])(action : T => Any) : Route =
     super.ajaxPost(path, form){ form =>
-      request.setAttribute("AJAX", "true")
+      request.setAttribute(Keys.Request.Ajax, "true")
       action(form)
     }
 
   protected def NotFound() =
-    if(request.hasAttribute("AJAX")){
+    if(request.hasAttribute(Keys.Request.Ajax)){
       org.scalatra.NotFound()
     } else {
       org.scalatra.NotFound(html.error("Not Found"))
     }
 
   protected def Unauthorized()(implicit context: app.Context) =
-    if(request.hasAttribute("AJAX")){
+    if(request.hasAttribute(Keys.Request.Ajax)){
       org.scalatra.Unauthorized()
     } else {
       if(context.loginAccount.isDefined){
@@ -135,10 +135,12 @@
    * Cached object are available during a request.
    */
   def cache[A](key: String)(action: => A): A =
-    Option(request.getAttribute("cache." + key).asInstanceOf[A]).getOrElse {
-      val newObject = action
-      request.setAttribute("cache." + key, newObject)
-      newObject
+    defining(Keys.Request.Cache(key)){ cacheKey =>
+      Option(request.getAttribute(cacheKey).asInstanceOf[A]).getOrElse {
+        val newObject = action
+        request.setAttribute(cacheKey, newObject)
+        newObject
+      }
     }
 
 }
diff --git a/src/main/scala/servlet/BasicAuthenticationFilter.scala b/src/main/scala/servlet/BasicAuthenticationFilter.scala
index 9a085ad..ad8a836 100644
--- a/src/main/scala/servlet/BasicAuthenticationFilter.scala
+++ b/src/main/scala/servlet/BasicAuthenticationFilter.scala
@@ -6,6 +6,7 @@
 import org.slf4j.LoggerFactory
 import util.Implicits._
 import util.ControlUtil._
+import util.Keys
 
 /**
  * Provides BASIC Authentication for [[servlet.GitRepositoryServlet]].
@@ -38,7 +39,7 @@
                 case null => requireAuth(response)
                 case auth => decodeAuthHeader(auth).split(":") match {
                   case Array(username, password) if(isWritableUser(username, password, repository)) => {
-                    request.setAttribute("USER_NAME", username)
+                    request.setAttribute(Keys.Request.UserName, username)
                     chain.doFilter(req, wrappedResponse)
                   }
                   case _ => requireAuth(response)
diff --git a/src/main/scala/servlet/GitRepositoryServlet.scala b/src/main/scala/servlet/GitRepositoryServlet.scala
index f385c98..309b025 100644
--- a/src/main/scala/servlet/GitRepositoryServlet.scala
+++ b/src/main/scala/servlet/GitRepositoryServlet.scala
@@ -9,7 +9,7 @@
 import javax.servlet.ServletConfig
 import javax.servlet.ServletContext
 import javax.servlet.http.HttpServletRequest
-import util.{JGitUtil, Directory}
+import util.{Keys, JGitUtil, Directory}
 import util.ControlUtil._
 import util.Implicits._
 import service._
@@ -55,7 +55,7 @@
   
   override def create(request: HttpServletRequest, db: Repository): ReceivePack = {
     val receivePack = new ReceivePack(db)
-    val userName = request.getAttribute("USER_NAME").asInstanceOf[String]
+    val userName = request.getAttribute(Keys.Request.UserName).asInstanceOf[String]
 
     logger.debug("requestURI: " + request.getRequestURI)
     logger.debug("userName:" + userName)
diff --git a/src/main/scala/util/Keys.scala b/src/main/scala/util/Keys.scala
index 9dae8d0..4aabe35 100644
--- a/src/main/scala/util/Keys.scala
+++ b/src/main/scala/util/Keys.scala
@@ -1,10 +1,13 @@
 package util
 
 /**
- * Define key strings for request attributes, session attributes or flash attributes..
+ * Define key strings for request attributes, session attributes or flash attributes.
  */
 object Keys {
 
+  /**
+   * Define session keys.
+   */
   object Session {
 
     /**
@@ -44,4 +47,26 @@
 
   }
 
+  /**
+   * Define request keys.
+   */
+  object Request {
+
+    /**
+     * Request key for the Ajax request flag.
+     */
+    val Ajax = "AJAX"
+
+    /**
+     * Request key for the username which is used during Git repository access.
+     */
+    val UserName = "USER_NAME"
+
+    /**
+     * Generate request key for the request cache.
+     */
+    def Cache(key: String) = s"cache.${key}"
+
+  }
+
 }