Scala4sling

Scala for Sling
Building RESTful Web Applications with Scala for Sling
http://people.apache.org/~mduerig/scala4sling/

Michael Dürig
Day Software AG
10080

LOGO SPEAKER‘S COMPANY

2

AGENDA

> Introduction

> What is Apache Sling?

> What is Scala?

> Scala for Sling

> Summary and questions

3

Introduction

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

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

4

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

5

AGENDA

> Introduction


> What is Scala?

> Scala for Sling


6

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)

7

URL decomposition

GET /forum/scala4sling.thread.html

8

URL decomposition


Repository

9

URL decomposition


Repository
Repository path

10

URL decomposition


Repository
Repository path

Application selection

11

URL decomposition


Repository
Repository path Script selection

Application selection

12

AGENDA

> Introduction


> What is Scala?

> Scala for Sling


13

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
– Great for creating DSLs

14

Type inference: the scripting touch

> Values
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

> Type parameters
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]

15

Type inference: the scripting touch

> Values
val x = 42 // x has type Int
val s = x.toString // s has type String
val q = s.substring(s) //
class Pair<S, T> type mismatch; found String, required Int
{
public final S s;
public final T t;

> Type parameters
public Pair(S s, T t) {
super();
class Pair[S, T](s: S, t: =T)
this.s s;
def makePair[S, T](s: S, t: t; = new Pair(s, t)
this.t = T)
}
val p = makePair(42.0, "Scala") // p has type Pair[Double, String]
}

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");

16

XML <pre>literals</pre>

> HTML? Scala!
val title = "Hello Jazoon 09"

println {
<html>
<body>
<h1>{ title }</h1>
{
(for (c <- title) yield c)
.mkString(" ")
}
</body>
</html>
}

17


> HTML? Scala!

println {
<html> println {
<body> Elem(null, "html", Null, TopScope,
<h1>{ title }</h1> "body", Null, TopScope,
Elem(null,
{ Elem(null, "h1", Null, TopScope,
Text(title)
.mkString(" ")
),
} Text(
</body> (for (c <- title) yield c)
</html> .mkString(" ")
} )
)
)
}

18


> HTML? Scala!

println {
<html>
<body>
<h1>{ title }</h1>
{
.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>

19

Implicits: pimp my library

> Implicit conversion
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

> Déjà vu?
– Similar to extension methods in C#
– Similar to conversion constructors in C++
– Equivalent to type classes in Haskell

20

Objects are functions are objects…

> Object as function
object Twice {
def apply(n: Int) = 2*n
}

println(Twice(21)) // prints 42

> Function as object
def twice(n: Int) = 2*n

val doubler = twice(_)
println(doubler(21)) // prints 42

21

AGENDA

> Introduction


> What is Scala?

> Scala for Sling


23

Forum: html.scala

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>
}
}

24

Forum: html.scala
GET /forum.html
package forum {
object html {
// ...

println {
<html>
<body>
</body>
</html>
}
}

25

Forum: html.scala

package forum {
object html {
Put Sling variables into scope
(currentNode, request, response, etc.)
// ...

println {
<html>
<body>
</body>
</html>
}
}

26

Forum: html.scala

package forum {
object html {
/**
// ... * Print out an object followed by a new line character.
* @param x the object to print.
*/
println { def println(x: Any): Unit = out.println(x)
<html>
<body>
</body>
</html>
}
}

27

Forum: html.scala

package forum {
object html {
/**
// ... * Print out an object followed by a new line character.
* @param x the object to print.
*/
println { def println(x: Any): Unit = out.println(x)
<html>
<body>
</body>
</html>
}
}

28

Forum: html.scala

package forum {
object html {
// implicit def rich(node: Node) = new {
...
def apply(property: String) = node.getProperty(property).getString
...
println {
}
<html>
<body>
</body>
</html>
}
}

29

Forum: thread overview

object ThreadOverview {
// imports omitted

def render(node: Node) =
emptyUnless(node.hasNodes) {
<h1>threads</h1>
<ul>{ node.nodes map toListItem }</ul>
}

private def toListItem(node: Node) = {
<li>
{ node("subject") }
(<a href={ node.path + ".thread.html"}>show thread</a>)
</li>
}
}

30

Forum: thread overview

object ThreadOverview {
def emptyUnless(condition: Boolean)(block: => NodeSeq) =
// imports omitted
if (condition) block
else Empty
def render(node: Node) =
emptyUnless(node.hasNodes) {
<h1>threads</h1>
<ul>{ node.nodes map toListItem }</ul>
}

private def toListItem(node: Node) = {
<li>
{ node("subject") }
(<a href={ node.path + ".thread.html"}>show thread</a>)
</li>
}
}

31

Forum: form data

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>
}
}

32

Forum: form data

def render = {

</form>
}
}

33

Forum: form data

def render = {
POST should add new child node to
/content/forum/

</form>
}
}

34

Forum: form data

def render = {
/content/forum/
<form action="/content/forum/*" with properties subject and body
... method="POST" of
type String,

</form>
}
}

35

Forum: form data

def render = {
/content/forum/
<form action="/content/forum/*" with properties subject and body
... method="POST" of
type String,

subject <input name="subject" and a child node logo of type nt:file.
... type="text" />
</form>
}
}

36

Forum: form data

def render = {

</form>
} Redirect to forum.html on success
}

37

Extracting form fields

> Sling post servlet
– No action required: used by default
– Creates nodes and properties for form fields
– Tweaked with hidden form fields
– Sensible defaults

> Custom POST request handler
– Write a script POST.scala
– Process form fields in code
– Full control over request processing

38

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"))
}
}

39

package forum { POST /forum.html
object POST {
// ...

}
session.save
}
}

40

package forum {
object POST {
// ... Add node for this post
}
session.save
}
}

41

package forum {
object POST {
// ...
Set properties for body and subject
}
session.save
}
}

42

package forum {
object POST {
// ...

If the request contains a logo
}
session.save
}
}

43

package forum {
object POST {
// ...

... add a child node logo of type nt:file
}
session.save
}
}

44

package forum {
object POST {
// ...

... add a child node logo of type nt:file
val logoNode = node.addNode("logo", set properties jcr:lastModified,
... and "nt:file")
jcr:mimeType and jcr:data
}
session.save
}
}

45

package forum {
object POST {
// ...

Save changes and send redirect
}
session.save
}
}

46

Forum: unit testing

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
}

47

Forum: unit testing

with MockItem

}

forum.html
}

48

Forum: unit testing

with MockItem

}

forum.html
}

49

Forum: unit testing
<html>
<head>
<link href="/apps/forum/static/blue.css" rel="stylesheet"></link>
</head>
<body>
<div id="Header">
Welcome to the forum
with MockItem
— Wed Jun 17 17:12:48 CEST 2009
</div>
<div id="Menu">
override def <p>search all threads:
request = new MockSlingHttpServletRequest
<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">
<span id="inp">
forum.html <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>

50

AGENDA

> Introduction


> What is Scala?

> Scala for Sling


51

Conclusion

> Advantages
– Scala!
– No language boundary
– Tool support (i.e. IDE, ScalaDoc,
safe refactoring, unit testing)

> Disadvantages
– IDE support shaky, improves
quickly though
– Not much refactoring support as
of today

52

Conclusion

> Advantages
– Scala!

> Disadvantages
quickly though
of today

53

Conclusion

> Advantages
– Scala!
<p>Welcome to { currentNode("name") } forum</p>
– No language boundary — { Calendar.getInstance.getTime }
– Tool support (i.e. IDE, ScalaDoc, { ThreadOverview.render(currentNode) }

> Disadvantages
quickly though
of today

54

Conclusion

> Advantages
– Scala!

> Disadvantages
quickly though
of today

55

Conclusion

> Advantages
– Scala!

> Disadvantages
quickly though
of today

56

Conclusion

> Advantages
– Scala!
object html_Bindings {
– Tool support (i.e. IDE, ScalaDoc, def currentNode = new MockNode
safe refactoring, unit testing) ...
}

> Disadvantages forum.html
}
quickly though
of today

57

Conclusion

> Advantages
– Scala!

> Disadvantages
quickly though
of today

58

Summary

> Apache Sling
– Great for building RESTful web applications
– Pluggable scripting support (JSR-223)

> Scala
– Great for scripting
– Supports «on the fly» templates through XML literals
– Easy unit testing

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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