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Scala & sling


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Apache Sling is a web application framework which eases development of content centric applications. Sling is based on REST principles and uses a JCR content repository (JSR-170/JSR-283) for storage. …

Apache Sling is a web application framework which eases development of content centric applications. Sling is based on REST principles and uses a JCR content repository (JSR-170/JSR-283) for storage. Based on the JSR 223 specification (Scripting for the Java Platform) it integrates various scripting languages as OSGi bundles.

Scala is a scalable programming language for the JVM which is fully interoperable with Java. It is designed to express common programming patterns in a concise, elegant, and type safe way. Scala smoothly bridges the gap between object oriented and functional paradigms. Despite being strongly typed, Scala has the touch and feel of a genuine scripting language. It has the ability to infer types of expressions rather than relying on the programmer to explicitly declare them. Scala thus combines the best of the two worlds: flexible scripting and strong tool support e.g. documentation, safe refactoring and fail fast compilation. Its flexible syntax lets programmers easily define their own internal DSLs, effectively extending the language without leaving it.

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  • 1. LOGO SPEAKER‘S COMPANY Scala for Sling Building RESTful Web Applications with Scala for Sling Michael Dürig Day Software AG 10080
  • 2. 2 Introduction > Michael Dürig – Developer for Day Software – > Michael Marth – Technology Evangelist for Day Software –
  • 3. 3 Overview > What to expect – Proof of concept – Experimental code > What not to expect – Product showcase, tutorial – Live coding (demo code available from > Prerequisites – Basic understanding of Java content repositories (JCR) – Prior exposure to Scala a plus
  • 4. 4 AGENDA > Introduction > What is Apache Sling? > What is Scala? > Scala for Sling > Summary and questions
  • 5. 5 Sling builds on JCR > Web application framework for JCR – JCR (JSR-170/JSR-283): Apache Jackrabbit – OSGi-based: Apache Felix – > Scriptable application layer for JCR – JSR-223: Scripting for the Java platform > REST over JCR – Content resolution for mapping request URLs to JCR nodes – Servlet resolution for mapping JCR nodes to request handlers (i.e. scripts)
  • 6. 6 URL decomposition GET /forum/scala4sling.thread.html Repository Repository path Script selection Application selection
  • 7. 7 AGENDA > Introduction > What is Apache Sling? > What is Scala? > Scala for Sling > Summary and questions
  • 8. 8 Scala builds on the JVM > Multi-paradigm language for the JVM – Conceived by Martin Odersky and his group (EPFL, Lausanne) – Fully interoperable with Java – IDE plugins for Eclipse and IntelliJ IDEA – > Concise, elegant, and type safe – Touch and feel of a genuine scripting language – Smoothly integrates object oriented and functional features – Ideal for creating internal DSLs
  • 9. > Values > Type parameters 9 Type inference: the scripting touch val x = 42 // x has type Int val s = x.toString // s has type String val q = s.substring(s) // type mismatch; found String, required Int class Pair[S, T](s: S, t: T) def makePair[S, T](s: S, t: T) = new Pair(s, t) val p = makePair(42.0, "Scala") // p has type Pair[Double, String] class Pair<S, T> { public final S s; public final T t; public Pair(S s, T t) { super(); this.s = s; this.t = t; } } public <S, T> Pair<S, T> makePair(S s, T t) { return new Pair<S, T>(s, t); } public final Pair<Double, String> p = makePair(42.0, "Scala");
  • 10. 10 XML <pre>literals</pre> > HTML? Scala! val title = "Hello Jazoon 09" println { Elem(null, "html", Null, TopScope, Elem(null, "body", Null, TopScope, Elem(null, "h1", Null, TopScope, Text(title) ), Text( (for (c <- title) yield c) .mkString(" ") ) ) ) } val title = "Hello Jazoon 09" println { <html> <body> <h1>{ title }</h1> { (for (c <- title) yield c) .mkString(" ") } </body> </html> } <html> <body> <h1>Hello Jazoon 09</h1> H e l l o J a z o o n 0 9 </body> </html>
  • 11. 11 Implicits: pimp my library > Implicit conversion > Déjà vu? – Similar to extension methods in C# – Similar to conversion constructors in C++ – Equivalent to type classes in Haskell implicit def translate(s: String) = new { def toGerman = s match { case "Example" => "Beispiel" // ... case _ => throw new Exception("No translation for " + s) } } val german = "Example".toGerman
  • 12. 12 AGENDA > Introduction > What is Apache Sling? > What is Scala? > Scala for Sling > Summary and questions
  • 13. 13 Demo application: Forum
  • 14. package forum { object html { import html_Bindings._ // ... println { <html> <body> Welcome to the { currentNode("name") } forum &mdash; { Calendar.getInstance.getTime } { ThreadNewForm.render } { ThreadOverview.render(currentNode) } </body> </html> } } GET /forum.html Put Sling variables into scope (currentNode, request, response, etc.)/** * Print out an object followed by a new line character. * @param x the object to print. */ def println(x: Any): Unit = out.println(x) 14 Forum: html.scala implicit def rich(node: Node) = new { def apply(property: String) = node.getProperty(property).getString ... }
  • 15. object ThreadNewForm { def render = { <h1>start a new thread</h1> <form action="/content/forum/*" method="POST" enctype="multipart/form-data"> subject <input name="subject" type="text" /> <textarea name="body"></textarea> logo <input name="logo“ type="file" /> <input type="submit" value="save" /> <input name=":redirect" value="/content/forum.html" type="hidden" /> </form> } } 15 Forum: form data POST should add new child node to /content/forum/ Redirect to forum.html on success ... with properties subject and body of type String, ... and a child node logo of type nt:file.
  • 16. 16 Forum: custom POST request handler package forum { object POST { import POST_Bindings._ // ... val node = addNodes(session.root, newPath) node.setProperty("body", request("body")) node.setProperty(“subject", request(“subject")) if (request("logo") != "") { val logoNode = node.addNode("logo", "nt:file") val contentNode = logoNode.addNode("jcr:content", "nt:resource") val logo = request.getRequestParameter("logo") contentNode.setProperty("jcr:lastModified", Calendar.getInstance) contentNode.setProperty("jcr:mimeType", logo.getContentType) contentNode.setProperty("jcr:data", logo.getInputStream) } response.sendRedirect(request(":redirect")) } } POST /forum.html Add node for this post Set properties for body and subject If the request contains a logo ... add a child node logo of type nt:file ... and set properties jcr:lastModified, jcr:mimeType and jcr:data Save changes and send redirect
  • 17. object html_Bindings extends MockBindings { override def currentNode = new MockNode with MockItem override def request = new MockSlingHttpServletRequest with MockHttpServletRequest with MockServletRequest } object Test extends Application { forum.html } 17 Forum: unit testing <html> <head> <link href="/apps/forum/static/blue.css" rel="stylesheet"></link> </head> <body> <div id="Header"> Welcome to the forum &mdash; Wed Jun 17 17:12:48 CEST 2009 </div> <div id="Menu"> <p>search all threads: <form action="/content/" enctype="multipart/form-data" method="GET"> <input value="" type="text" size="10" name="query"></input> <input value="search" type="submit"></input> </form> </p> </div> <div id="Content"> <h1>start a new thread</h1> <span id="inp"> <form action="/content/forum/*" enctype="multipart/form-data" method="POST"> <p>subject</p> <p><input type="text" name="subject"></input></p> <p><textarea name="body"></textarea></p> <p>logo</p> <p><input type="file" name="logo"></input></p> <p><input value="save" type="submit"></input></p> <input value="/content/forum.html" type="hidden" name=":redirect"></input> </form> </span> </div> </body> </html>
  • 18. 18 AGENDA > Introduction > What is Apache Sling? > What is Scala? > Scala for Sling > Summary and questions
  • 19. 19 Conclusion > Advantages – Scala! – No language boundary: «on the fly» templates through XML literals – Tool support (i.e. IDE, ScalaDoc, safe refactoring, unit testing) > Disadvantages – IDE support shaky, improves quickly though – Not much refactoring support as of today object html_Bindings { def currentNode = new MockNode ... } object Test extends Application { forum.html } <p>Welcome to { currentNode("name") } forum</p> &mdash; { Calendar.getInstance.getTime } { ThreadNewForm.render } { ThreadOverview.render(currentNode) }
  • 20. LOGO SPEAKER‘S COMPANY Michael Dürig Michael Marth Day Software AG References: • Scala for Sling: • The Scala programming language: • Apache Sling: