Scala & sling

LOGO SPEAKER‘S COMPANY
Scala for Sling
Building RESTful Web Applications with Scala for Sling
http://people.apache.org/~mduerig/scala4sling/
Michael Dürig
Day Software AG
10080

2
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

4
AGENDA
> Introduction
> What is Apache Sling?
> What is Scala?
> Scala for Sling
> Summary and questions

5
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)

6
URL decomposition
GET /forum/scala4sling.thread.html
Repository
Repository path Script selection
Application selection

7
AGENDA
> Introduction
> What is Scala?
> Scala for Sling

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
– 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
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
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
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
AGENDA
> Introduction
> What is Scala?
> Scala for Sling

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)
14
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>
}
}
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
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)
}
session.save
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

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
— 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>

18
AGENDA
> Introduction
> What is Scala?
> Scala for Sling

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

LOGO SPEAKER‘S COMPANY
Michael Dürig michael.duerig@day.com
Michael Marth michael.marth@day.com
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/

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