Scala & sling

LOGO SPEAKER‘S COMPANY

Scala for SlingBuilding RESTful Web Applications with Scala for Slinghttp://people.apache.org/~mduerig/scala4sling/

Michael Dürig

Day Software AG

10080

http://people.apache.org/~mduerig/scala4sling/

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Introduction

> Michael Dürig– Developer for Day Software– http://michid.wordpress.com/

> Michael Marth– Technology Evangelist for Day Software– http://dev.day.com/

3

Overview

> What to expect– Proof of concept– Experimental code

> What not to expect– Product showcase, tutorial– Live coding (demo code available from

http://people.apache.org/~mduerig/scala4sling/)

> Prerequisites– Basic understanding of Java content repositories (JCR)– Prior exposure to Scala a plus

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AGENDA

> Introduction

> What is Apache Sling?

> What is Scala?

> Scala for Sling

> Summary and questions

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Sling builds on JCR

> Web application framework for JCR– JCR (JSR-170/JSR-283): Apache Jackrabbit – OSGi-based: Apache Felix– http://incubator.apache.org/sling/

> 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)

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URL decomposition

GET /forum/scala4sling.thread.html

RepositoryRepository path Script selection

Application selection

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AGENDA

> Introduction


> What is Scala?

> Scala for Sling


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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 – http://www.scala-lang.org/

> 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

> Values

> Type parameters

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Type inference: the scripting touch

val x = 42 // x has type Intval s = x.toString // s has type Stringval 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");

Scala vs. Java3 vs. 13 LOC!

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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>}

Syntactic sugar

<html> <body> <h1>Hello Jazoon 09</h1> H e l l o J a z o o n 0 9 </body> </html>

System.out

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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

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AGENDA

> Introduction


> What is Scala?

> Scala for Sling


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Demo application: Forum

package forum {

object html {

import html_Bindings._

// ...

println {

<html>

<body>

Welcome to the { currentNode("name") } forum

— { 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)

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Forum: html.scala

implicit def rich(node: Node) = new { def apply(property: String) = node.getProperty(property).getString ...}

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>

}

}

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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.

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Forum: custom POST request handlerpackage 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) }

session.save response.sendRedirect(request(":redirect")) }}

POST /forum.html

Add node for this postSet 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

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

}

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Forum: unit testing<html> <head> <link href="/apps/forum/static/blue.css" rel="stylesheet"></link> </head> <body> <div id="Header"> Welcome to the forum — Wed Jun 17 17:12:48 CEST 2009 </div> <div id="Menu"> <p>search all threads: <form action="/content/forum.search.html" 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>

System.out

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AGENDA

> Introduction


> What is Scala?

> Scala for Sling


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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> — { Calendar.getInstance.getTime } { ThreadNewForm.render }{ ThreadOverview.render(currentNode) }

LOGO SPEAKER‘S COMPANY

Michael Dürig [email protected]

Michael Marth [email protected]

Day Software AG http://www.day.com/

References:

• Scala for Sling: http://people.apache.org/~mduerig/scala4sling/

• The Scala programming language: http://www.scala-lang.org/

• Apache Sling: http://incubator.apache.org/sling/

http://www.day.com/

http://people.apache.org/~mduerig/scala4sling/

http://www.scala-lang.org/

http://incubator.apache.org/sling/

Scala & sling

Technology

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