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Tiny Scala web framework, inspired by Sinatra
Scala JavaScript
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Scalatra is a tiny, Sinatra-like web framework for Scala.


import org.scalatra._

class ScalatraExample extends ScalatraServlet {
  get("/") {
    <h1>Hello, world!</h1>

Quick start

  1. Git-clone the prototype. Alternatively, download and extract a tarball or zip.

     $ git clone git:// my-app
  2. Change directory into your clone.

     $ cd my-app
  3. Launch SBT.

     $ sbt
  4. Fetch the dependencies.

     > update
  5. Start Jetty, enabling continuous compilation and reloading.

     > jetty-run
     > ~prepare-webapp
  6. Browse to http://localhost:8080/.

  7. Start hacking on src/main/scala/MyScalatraFilter.scala.

Note: if you keep getting frequent OutOfMemory errors from sbt you can try changing its script as described in this document so that it executes this command line:

 java -XX:+CMSClassUnloadingEnabled -XX:MaxPermSize=256m -Xmx512M -Xss2M -jar `dirname $0`/sbt-launch.jar "$@"

Note 2: if you already have a checkout, and after a git pull the build fails, try to explicitly run the update and clean sbt tasks before running compile.

Alternative Maven quickstart.

See the simple-scalatra-archetype.


Mailing list

The scalatra-user mailing list is open to anybody. It is the best place to ask questions, so everybody can see the answer.

IRC channel

For those topics that are easier to discuss in real time, or just to hang out with some fun people, join us on the #scalatra channel on


In Scalatra, a route is an HTTP method paired with a URL matching pattern.

get("/") { 
  // show something 

post("/") { 
  // submit/create something 

put("/") { 
  // update something 

delete("/") { 
  // delete something 

Route order

The first matching route is invoked. Routes are matched from the bottom up. This is the opposite of Sinatra. Route definitions are executed as part of a Scala constructor; by matching from the bottom up, routes can be overridden in child classes.

Path patterns

Path patterns add parameters to the params map. Repeated values are accessible through the multiParams map.

Named parameters

Route patterns may include named parameters:

get("/hello/:name") {
  // Matches "GET /hello/foo" and "GET /hello/bar"
  // params("name") is "foo" or "bar"
  <p>Hello, {params("name")}</p>


Route patterns may also include wildcard parameters, accessible through the splat key.

get("/say/*/to/*) {
  // Matches "GET /say/hello/to/world"
  multiParams("splat") # == Seq("hello", "world")

get("/download/*.*) {
  // Matches "GET /download/path/to/file.xml"
  multiParams("splat") # == Seq("path/to/file", "xml")

Regular expressions

The route matcher may also be a regular expression. Capture groups are accessible through the captures key.

get("""^\/f(.*)/b(.*)""".r) {
  // Matches "GET /foo/bar"
  multiParams("captures") # == Seq("oo", "ar") 

Path patterns in the REPL

If you want to experiment with path patterns, it's very easy in the REPL.

scala> import org.scalatra.pattern._
import org.scalatra.pattern._

scala> val pattern = PathPatternParser.parseFrom("/foo/:bar")
pattern: PathPattern = PathPattern(^/foo/([^/?]+)$,List(bar))

scala> pattern("/y/x") // doesn't match 
res1: Option[MultiParams] = None

scala> pattern("/foo/x") // matches
res2: Option[MultiParams] = Some(Map(bar -> ListBuffer(x)))

Obligatory scolding: the REPL is not a substitute for proper unit tests!

Rails-like pattern matching

By default, route patterns parsing is based on Sinatra. Rails has a similar, but not identical, syntax, based on Rack::Mount's Strexp. The path pattern parser is resolved implicitly, and may be overridden if you prefer an alternate syntax:

import org.scalatra._

class RailsLikeRouting extends ScalatraFilter {
  implicit override def string2RouteMatcher(path: String) =

  get("/:file(.:ext)") { // matched Rails-style }


Routes may include conditions. A condition is any expression that returns Boolean. Conditions are evaluated by-name each time the route matcher runs.

get("/foo") {
  // Matches "GET /foo"

get("/foo", request.getRemoteHost == "") {
  // Overrides "GET /foo" for local users

Multiple conditions can be chained together. A route must match all conditions:

get("/foo", request.getRemoteHost == "", request.getRemoteUser == "admin") {
  // Only matches if you're the admin, and you're localhost

No path pattern is necessary. A route may consist of solely a condition:

get(isMaintenanceMode) {
  <h1>Go away!</h1>


Each route is followed by an action. An Action may return any value, which is then rendered to the response according to the following rules:

If no content-type is set, it is set to `application/octet-stream`. The byte array is written to the response's output stream.
If no content-type is set, it is set to`text/html`. The node sequence is converted to a string and written to the response's writer.
This signifies that the action has rendered the entire response, and no further action is taken.
For any other value, if the content type is not set, it is set to `text/plain`. The value is converted to a string and written to the response's writer

This behavior may be customized for these or other return types by overriding renderResponse.


Before filters are evaluated before each request within the same context as the routes.

before {
  // Default all responses to text/html
  contentType = "text/html"

After filters are evaluated after each request, but before the action result is rendered, within the same context as the routes.

after {
  if (response.status >= 500)
    println("OMG! ONOZ!")


To immediately stop a request within a filter or route:


You can also specify the status:


Or the body:

halt("This will be the body")

Or both:

halt(401, "Go away!")


A route can punt processing to the next matching route using pass. Remember, unlike Sinatra, routes are matched from the bottom up.

get("/guess/*") {
  "You missed!"

get("/guess/:who") {
  params("who") match {
    case "Frank" => pass()
    case _ => "You got me!"

The route block is immediately exited and control continues with the next matching route. If no matching route is found, a 404 is returned.

Accessing the Servlet API


The request is available through the request variable. The request is implicitly extended with the following methods:

  1. body: to get the request body as a string
  2. isAjax: to detect AJAX requests
  3. cookies and multiCookies: a Map view of the request's cookies
  4. Implements scala.collection.mutable.Map backed by request attributes


The response is available through the response variable.


The session is available through the session variable. The session implicitly implements scala.collection.mutable.Map backed by session attributes. To avoid creating a session, it may be accessed through sessionOption.


The servlet context is available through the servletContext variable. The servlet context implicitly implements scala.collection.mutable.Map backed by servlet context attributes.


The environment is defined by: 1. The org.scalatra.environment system property. 2. The org.scalatra.environment init property. 3. A default of development.

If the environment starts with "dev", then isDevelopmentMode returns true. This flag may be used by other modules, for example, to enable the Scalate console.

Error handling

Error handlers run within the same context as routes and before filters.

Not Found

Whenever no route matches, the notFound handler is invoked:

notFound {
  <h1>Not found.  Bummer.</h1>


The error handler is invoked any time an exception is raised from a route block or a filter. The throwable can be obtained from the caughtThrowable instance variable. This variable is not defined outside the error block.

error {

Flash scope

Flash scope is available by mixing in FlashMapSupport, which provides a mutable map named flash. Values put into flash scope during the current request are stored in the session through the next request and then discarded. This is particularly useful for messages when using the Post/Redirect/Get pattern.

Templating with Scalate

Scalatra provides optional support for Scalate, a Scala template engine.

  1. Depend on scalatra-scalate.jar and a slf4j binding. In your SBT build:

    val scalatraScalate = "org.scalatra" %% "scalatra-scalate" % scalatraVersion val slf4jBinding = "ch.qos.logback" % "logback-classic" % "0.9.25" % runtime

  2. Extend your application with ScalateSupport

    import org.scalatra._ import org.scalatra.scalate._

    class MyApplication extends ScalatraServlet with ScalateSupport { // .... }

  3. A template engine is created as the templateEngine variable. This can be used to render templates and call layouts.

    get("/") { templateEngine.layout("index.scaml", "content" -> "yada yada yada") }

Additionally, createRenderContext may be used to create a render context for the current request and response.

Finally, the Scalate Console is enabled in development mode to display any unhandled exceptions.

File upload support

Scalatra provides optional support for file uploads with Commons FileUpload.

  1. Depend on scalatra-fileupload.jar. In your SBT build:

    val scalatraFileUpload = "org.scalatra" %% "scalatra-fileupload" % scalatraVersion

  2. Extend your application with FileUploadSupport

    import org.scalatra.ScalatraServlet
    import org.scalatra.fileupload.FileUploadSupport
    class MyApp extends ScalatraServlet with FileUploadSupport {
      // ...
  3. Be sure that your form is of type multipart/form-data:

    get("/") {
      <form method="post" enctype="multipart/form-data">
        <input type="file" name="foo" />
        <input type="submit" />
  4. Your files are available through the fileParams or fileMultiParams maps:

    post("/") {

WebSocket and Comet support through Socket.IO

Scalatra provides optional support for websockets and comet through We depend on the socketio-java project to provide this support.

  1. Depend on the scalatra-socketio.jar. In your SBT build:

    val scalatraSocketIO = "org.scalatra" %% "scalatra-socketio" % scalatraVersion

  2. SocketIO mimics a socket connection so it's easiest if you just create a socketio servlet at /*

    import org.scalatra.ScalatraServlet import org.scalatra.socketio.SocketIOSupport

    class MySocketIOServlet extends ScalatraServlet with SocketIOSupport { // ... }

  3. Setup the callbacks

    socketio { socket =>

     socket.onConnect { connection =>
       // Do stuff on connection
     socket.onMessage { (connection, frameType, message) =>
       // Receive a message
       // use `connection.send("string")` to send a message
       // use `connection.broadcast("to send")` to send a message to all connected clients except the current one
       // use `connection.disconnect` to disconnect the client.
     socket.onDisconnect { (connection, reason, message) =>
       // Do stuff on disconnection


  4. Add the necessary entries to web.xml

    SocketIOServlet com.example.SocketIOServlet flashPolicyServerHost localhost flashPolicyServerPort 843 flashPolicyDomain localhost flashPolicyPorts 8080

When you want to use websockets with jetty the sbt build tool gets in the way and that makes it look like the websocket stuff isn't working. If you deploy the war to a jetty distribution everything should work as expected.

Testing Your Scalatra Applications

Scalatra includes a test framework for writing the unit tests for your Scalatra application. The framework lets you send requests to your app and examine the response. It can be mixed into the test framework of your choosing; integration with ScalaTest and Specs is already provided. ScalatraTests supports HTTP GET/POST tests with or without request parameters and sessions. For more examples, please refer to core/src/test/scala.



  • scalatra-scalatest


Mix in ShouldMatchers or MustMatchers to your taste...

class MyScalatraServletTests extends ScalatraFunSuite with ShouldMatchers {
  // `MyScalatraServlet` is your app which extends ScalatraServlet
  addServlet(classOf[MyScalatraServlet], "/*")

  test("simple get") {
    get("/path/to/something") {
      status should equal (200)
      body should include ("hi!")



  • scalatra-specs


object MyScalatraServletTests extends ScalatraSpecification {
  addServlet(classOf[MyScalatraServlet], "/*")

  "MyScalatraServlet when using GET" should {
    "/path/to/something should return 'hi!'" in {
      get("/") {
        status mustEqual(200)
        body mustEqual("hi!")

Other test frameworks


  • scalatra-test

Usage guide

Create an instance of org.scalatra.test.ScalatraTests. Be sure to call start() and stop() before and after your test suite.

Maven Repository

To make usage of Scalatra as a dependency convenient, Maven hosting is now available courtesy of Sonatype.


There is a new authentication middleware in the auth directory, to be documented soon. See an example at usage example. Another example for basic authentication can be found

To use it from an SBT project, add the following to your project:

val auth = "org.scalatra" %% "scalatra-auth" % scalatraVersion


It looks neat, but is it production-ready?

  • It is use in the backend for LinkedIn Signal.

  • ChaCha is using it in multiple internal applications.

  • A project is in currently development to support a site with over one million unique users.

Are you using Scalatra in production? Tell us your story on the mailing list.

ScalatraServlet vs. ScalatraFilter

The main difference is the default behavior when a route is not found. A filter will delegate to the next filter or servlet in the chain (as configured by web.xml), whereas a ScalatraServlet will return a 404 response.

Another difference is that ScalatraFilter matches routes relative to the WAR's context path. ScalatraServlet matches routes relative to the servlet path. This allows you to mount multiple servlets under in different namespaces in the same WAR.

Use ScalatraFilter if:

  • You are migrating a legacy application inside the same URL space
  • You want to serve static content from the WAR rather than a dedicated web server

Use ScalatraServlet if:

  • You want to match routes with a prefix deeper than the context path.

Migration Guide

scalatra-2.0.0.M2 to scalatra-2.0.0.M3

Should be compatible. If it broke, please share your tale of woe on the mailing list.

scalatra-2.0.0.M1 to scalatra-2.0.0.M2

  1. Session has been retrofitted to a Map interface. get now returns an option instead of the value.
  2. ScalaTest support has been split off into scalatra-scalatest module. ScalatraSuite moved to org.scalatest.test.scalatest package, and no longer extends FunSuite in order to permit mixing in a BDD trait. You may either use ScalatraFunSuite or explicitly extend FunSuite yourself.

Step to Scalatra

Scalatra was renamed from Step to Scalatra to avoid a naming conflict with (an unrelated web framework)[]. scalatra-1.2.1 is identical to step-1.2.0 with the following exceptions:

  1. The package has changed from com.thinkminimo.step to org.scalatra.
  2. The Step class has been renamed to ScalatraServlet.
  3. All other Step* classes have been renamed to Scalatra*.

Related Projects

  • SSGI: Work in progress. Will provide an abstraction layer allowing a future version of Scalatra to run on web servers other than Servlet containers.

  • Bowler: A RESTful, multi-channel ready web framework in Scala with a functional flavour, built on top of Scalatra and Scalate.

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