The document describes Apache Sling, an OSGi-based application framework for building RESTful web applications on top of a content repository. It uses Apache Sling to build a sample coffee shop ordering application called Slingbucks. The application is built with only a few hundred lines of Java code and uses content to define things like coffee options and styles rather than hardcoding them. Apache Sling promotes the principle that "everything is content" and enables building full-featured applications with relatively little code by leveraging out-of-the-box HTTP services and the ability to extend functionality through OSGi plugins.

1. Bertrand Delacrétaz
Senior Developer, CQ5 R&D team, Adobe Basel
Apache Software Foundation Member and (current) Director
@bdelacretaz - http://grep.codeconsult.ch
Lausanne, May 2013
slides revision: 2013-05-30
1
RESTfulwebapps
withApacheSling

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Apache Sling: OSGi-based applications layer for JCR
2
content
everything is

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Everything is content!
3
Any app that requires more than
curl as a minimal client should
have a good reason.
Java
content
repository
JCR API
Apache SlingHTTP
Let’sbuildan
intelligentWeb
server.

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Content?
4
design
everything
website
code

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Website Content
5
/content
/geometrixx
/en
/company
/jcr:content
/par
/title
sling:resourceType
drives rendering

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Apache Sling
«any» scripting
languagescript == servlet
OSGi-
based
RESTful default servlets
sling.apache.org

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Sling Architecture Overview
7
OSGi framework
(Apache Felix)
WebDAV
server
Felix OSGi
console
JCR
content
repository
JCR API
ECMAscript
JSP
Ruby
Velocity
JSR 223
scripting
resource
resolution
servlet/
script
standard
servlets
custom
servlets
Sling Core

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Sling is based on OSGi
Extreme modularity
Fosters better structured code
Dynamic plugins - for everything!
In-JVM Service-based architecture
8
OSGi bundle
Private packages
Public packages
Metadata
Matchless picture: Alvimann on morguefile.com

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Clean URLs with Sling: «Reclaiming the Web»
Sling
/cars/audi/s4.details.html
Content
Repository
Path
Selectorsand
extension
9
sling:resourceType

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Sling Sample Application
Slingbucksa RESTful coffee shop
10

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Slingbucks Application Flow
Customers,
public content
Staff,
private content
11

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Slingbucks use cases: Order Coffee
Display order form with configurable options.
Customer submits order.
Redisplay order for confirmation with hard to guess ID.
1
Content:
12
POST

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Slingbucks use cases: Confirm Order
Redisplay order form.
Customer either modifies and
recalculates price, or confirms order.
1
2Content:
13
POST
GET

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Slingbucks Process Order use case and content
Confirmed order moves under /private, for Slingbucks staff
App displays a list of confirmed orders to staff.
Staff delivers order and deletes it from list.
3 Orders really move!
14

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Slingbucks Resources Design
Security/ACLs
MeaningfulURLs
1:1JCRpathmapping
Object-oriented design?
No: everything is content: we want RESTful resources.
15
New order form:
http://slingbucks.com/public/orders.html
Order editing and confirmation (example):
http://slingbucks.com/public/orders/544da609.html
Price of an order:
Same but ending with .price.html selector
List of confirmed orders:
http://slingbucks.com/private/confirmed.html

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Sling gets the Web!
16
allyouneediscurlor any other HTTP client

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The SlingPostServlet
$ curl -D -
-F "customerName=Bob The Geek"
-F sling:resourceType=slingbucks/order
-F lastModified=""
-F opt_coffeetype=capuccino
-F opt_size=medium
-F opt_sugar=raw
-F opt_cup=rosewood
http://u:pwd@slingserver/content/slingbucks/public/orders/
HTTP/1.1 201 Created
Location: /slingbucks/public/orders/117936075d4de452cbba5b468
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SlingPostServlet
JCR
content
repository
JCR API
HTTP POST

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Default JSON GET servlet
$ curl http://localhost:8080/content
/slingbucks/public/orders
/fad01d62ca54209a1405e3b.tidy.json
{
"opt_size": "small",
"customerName": "Bob the Geek",
"opt_coffeetype": "espresso",
"opt_sugar": "none",
"sling:resourceType": "slingbucks/order",
"opt_cup": "plastic",
"lastModified": "Nov 01 2010 18:31:01",
"jcr:primaryType": "nt:unstructured"
}
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DefaultGetServlet
JCR
content
repository
JCR API
HTTP GET
JSON

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Slingbucks Sample App
codeJust two OSGi services
and a few presentation scripts
19
Writinglotsof
code?
Maybeyou
shouldn’t

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Code: OSGi plugin for hard to guess node names
20
/** OSGi SCR instantiates this and registers as Service */
@Component
@Service
public class HexNodeNameGenerator
implements org.apache.sling..NodeNameGenerator {
@Override
/** Sling calls this when creating a node */
public String getNodeName(
SlingHttpServletRequest request,
String parentPath, ...)
{
...if path is in slingbucks tree:
return computeHardToGuessName();
...else return null
maven-scr-
plugin
processes

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Code: watch repository to move confirmed orders
/** OSGi SCR instantiates this */
@Component
public class ConfirmedOrdersObserver
implements EventListener, Runnable {
/** OSGi SCR provides this */
@Reference
private SlingRepository repository;
/** OSGi SCR calls this at startup */
protected void activate(ComponentContext ctx){
// Register with repository
// to callback our onEvent method
// on changes under /content/slingbucks/orders
...
public void onEvent(EventIterator it) {
while (it.hasNext()) {
if(path.endsWith(«orderConfirmed») {
... if orderConfirmed property is true:
... move node under private/
confirmed
... using
session.getWorkspace().move(....
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Orders really move!
TwoJava
methodsina
Component

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Coffee options? defined by content -
"fields" : {
"coffeetype" : {
"jcr:title" : "Coffee type",
"espresso" : {
"jcr:title" : "Espresso",
"jcr:description" : "The Italian job",
"priceOffset" : 2.20
},
"capuccino" : {
"jcr:title" : "Capuccino",
"jcr:description" : "The one with cream on top",
"priceOffset" : 3.40
}
},
"size" : {
"jcr:title" : "Size",
"small" : {
"jcr:title" : "Small",
"jcr:description" : "1dl",
"priceFactor" : 1
},
"large" : {
"jcr:title" : "Large",
"jcr:description" : "5dl",
"priceFactor" : 2
}
}
HTTP GET with .json
extension.
POST to set values.
(out of the box)
22
Reconfigure
in-flight
withcurl!

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Slingbucks code size
Java code: 250 lines
3 java files
HTML representation scripts: 250 lines
7 esp files
Initial repository content: 85 lines
3 json files
Style and client-side javascript: 43 lines
1 css and 1 js file
Scripts and design
content:
23
Writinglotsofcode?
Maybeyoushouldn’t

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Did I mention this already?
Sling design promotes RESTful applications.
Powerful out of the box HTTP services.
OSGi plugins for (most) everything.
24
Java
content
repository
JCR API
Apache Sling
Writinglotsof
code?
Maybeyou
shouldn’t
everything
is
content!

25. © 2011 Adobe Systems Incorporated. All Rights Reserved. Adobe Confidential.
Where next?
25
Code at http://s.apache.org/slingbucks
Code and community at sling.apache.org
OSGi info at www.osgi.org
Slides at www.slideshare.net/bdelacretaz