diff --git a/src/main/scala/app/ControllerBase.scala b/src/main/scala/app/ControllerBase.scala
index 1cc5f13..c1189ee 100644
--- a/src/main/scala/app/ControllerBase.scala
+++ b/src/main/scala/app/ControllerBase.scala
@@ -34,6 +34,17 @@
     url.substring(0, url.length - request.getRequestURI.length)
   }
 
+  protected def identifier: Constraint = new Constraint(){
+    def validate(name: String, value: String): Option[String] =
+      if(!value.matches("^[a-zA-Z0-9\\-_]+$")){
+        Some("%s contains invalid character.".format(name))
+      } else if(value.startsWith("_") || value.startsWith("-")){
+        Some("%s starts with invalid character.".format(name))
+      } else {
+        None
+      }
+  }
+
 }
 
 case class Context(path: String, loginAccount: Option[Account])
\ No newline at end of file
diff --git a/src/main/scala/app/CreateRepositoryController.scala b/src/main/scala/app/CreateRepositoryController.scala
index 17d4d50..0430077 100644
--- a/src/main/scala/app/CreateRepositoryController.scala
+++ b/src/main/scala/app/CreateRepositoryController.scala
@@ -21,7 +21,7 @@
   case class RepositoryCreationForm(name: String, description: Option[String])
 
   val form = mapping(
-    "name"        -> trim(label("Repository name", text(required, maxlength(40), repository))),
+    "name"        -> trim(label("Repository name", text(required, maxlength(40), identifier, unique))),
     "description" -> trim(label("Description"    , optional(text())))
   )(RepositoryCreationForm.apply)
 
@@ -81,20 +81,11 @@
   })
   
   /**
-   * Constraint for the repository name.
+   * Duplicate check for the repository name.
    */
-  def repository: Constraint = new Constraint(){
-    def validate(name: String, value: String): Option[String] = {
-      if(!value.matches("^[a-zA-Z0-9\\-_]+$")){
-        Some("Repository name contains invalid character.")
-      } else if(value.startsWith("_") || value.startsWith("-")){
-        Some("Repository name starts with invalid character.")
-      } else if(getRepositoryNamesOfUser(context.loginAccount.get.userName).contains(value)){
-        Some("Repository already exists.")
-      } else {
-        None
-      }
-    }
+  private def unique: Constraint = new Constraint(){
+    def validate(name: String, value: String): Option[String] =
+      getRepositoryNamesOfUser(context.loginAccount.get.userName).find(_ == value).map(_ => "Repository already exists.")
   }
   
 }
\ No newline at end of file
diff --git a/src/main/scala/app/SettingsController.scala b/src/main/scala/app/SettingsController.scala
index 459c883..88637fc 100644
--- a/src/main/scala/app/SettingsController.scala
+++ b/src/main/scala/app/SettingsController.scala
@@ -130,7 +130,7 @@
   /**
    * Provides Constraint to validate the collaborator name.
    */
-  def collaborator: Constraint = new Constraint(){
+  private def collaborator: Constraint = new Constraint(){
     def validate(name: String, value: String): Option[String] = {
       getAccountByUserName(value) match {
         case None => Some("User does not exist.")
diff --git a/src/main/scala/app/UsersController.scala b/src/main/scala/app/UsersController.scala
index cd5d0df..0e4f732 100644
--- a/src/main/scala/app/UsersController.scala
+++ b/src/main/scala/app/UsersController.scala
@@ -12,7 +12,7 @@
   case class UserForm(userName: String, password: String, mailAddress: String, isAdmin: Boolean, url: Option[String])
   
   val newForm = mapping(
-    "userName"    -> trim(label("Username"     , text(required, maxlength(100), username, unique))),
+    "userName"    -> trim(label("Username"     , text(required, maxlength(100), identifier, unique))),
     "password"    -> trim(label("Password"     , text(required, maxlength(100)))),
     "mailAddress" -> trim(label("Mail Address" , text(required, maxlength(100)))),
     "isAdmin"     -> trim(label("User Type"    , boolean())),
@@ -20,7 +20,7 @@
   )(UserForm.apply)
 
   val editForm = mapping(
-    "userName"    -> trim(label("Username"     , text(required, maxlength(100), username))),
+    "userName"    -> trim(label("Username"     , text(required, maxlength(100), identifier))),
     "password"    -> trim(label("Password"     , text(required, maxlength(100)))),
     "mailAddress" -> trim(label("Mail Address" , text(required, maxlength(100)))),
     "isAdmin"     -> trim(label("User Type"    , boolean())),
@@ -68,17 +68,6 @@
     redirect("/admin/users")
   })
 
-  private def username: Constraint = new Constraint(){
-    def validate(name: String, value: String): Option[String] =
-      if(!value.matches("^[a-zA-Z0-9\\-_]+$")){
-        Some("Username contains invalid character.")
-      } else if(value.startsWith("_") || value.startsWith("-")){
-        Some("Username starts with invalid character.")
-      } else {
-        None
-      }
-  }
-
   private def unique: Constraint = new Constraint(){
     def validate(name: String, value: String): Option[String] =
       getAccountByUserName(value).map { _ => "User already exists." }
diff --git a/src/main/scala/app/WikiController.scala b/src/main/scala/app/WikiController.scala
index ecc9305..cb709e5 100644
--- a/src/main/scala/app/WikiController.scala
+++ b/src/main/scala/app/WikiController.scala
@@ -14,14 +14,14 @@
   case class WikiPageEditForm(pageName: String, content: String, message: Option[String], currentPageName: String)
   
   val newForm = mapping(
-    "pageName"        -> trim(label("Page name"          , text(required, maxlength(40), pageName, unique))), 
+    "pageName"        -> trim(label("Page name"          , text(required, maxlength(40), identifier, unique))),
     "content"         -> trim(label("Content"            , text(required))),
     "message"         -> trim(label("Message"            , optional(text()))),
     "currentPageName" -> trim(label("Current page name"  , text()))
   )(WikiPageEditForm.apply)
   
   val editForm = mapping(
-    "pageName"        -> trim(label("Page name"          , text(required, maxlength(40), pageName))), 
+    "pageName"        -> trim(label("Page name"          , text(required, maxlength(40), identifier))),
     "content"         -> trim(label("Content"            , text(required))),
     "message"         -> trim(label("Message"            , optional(text()))),
     "currentPageName" -> trim(label("Current page name"  , text(required)))
@@ -176,22 +176,7 @@
     }
   })
 
-  /**
-   * Constraint for the wiki page name.
-   */
-  def pageName: Constraint = new Constraint(){
-    def validate(name: String, value: String): Option[String] = {
-      if(!value.matches("^[a-zA-Z0-9\\-_]+$")){
-        Some("Page name contains invalid character.")
-      } else if(value.startsWith("_") || value.startsWith("-")){
-        Some("Page name starts with invalid character.")
-      } else {
-        None
-      }
-    }
-  }
-  
-  def isWritable(owner: String, repository: String): Boolean = {
+  private def isWritable(owner: String, repository: String): Boolean = {
     context.loginAccount match {
       case Some(a) if(a.isAdmin) => true
       case Some(a) if(a.userName == owner) => true
@@ -199,15 +184,10 @@
       case _ => false
     }
   }
-  
-  def unique: Constraint = new Constraint(){
-    def validate(name: String, value: String): Option[String] = {
-      if(getWikiPageList(params("owner"), params("repository")).contains(value)){
-        Some("Page already exists.")
-      } else {
-        None
-      }
-    }
+
+  private def unique: Constraint = new Constraint(){
+    def validate(name: String, value: String): Option[String] =
+      getWikiPageList(params("owner"), params("repository")).find(_ == value).map(_ => "Page already exists.")
   }
 
 }
\ No newline at end of file