Apache Sling is a RESTful content-centric web application framework built on OSGi and JCR standards. It allows resources to be accessed via URLs and supports scripting languages like JSP and JavaScript to render resources. Sling follows REST principles where resources are independent of representations and identified through URLs. It differs from traditional MVC frameworks by treating everything as a resource rather than distinguishing between controllers, models, and views. Sling uses OSGi bundles, a JCR repository like Jackrabbit to store content, and a scripting engine to handle requests and return representations of resources.

1. RESTful development
with Apache Sling
Sergii Fesenko

2. What is Apache Sling?
● Content centric web application framework
● Built around RESTful principles
● Powered by OSGI and JCR
● Apache Open Source project
● Supports Scripting (JSR-233)
● Implemented in Java

3. Sling history
● Sling started as an internal project at Day Software, and entered the Apache
Incubator in September 2007.
● Apache a top level project since 2009
● Name refers the weapon David uses to slay the giant Goliath
(simplest device for delivering content very fast)

4. Who is using Sling
Teaching and
learning open source
environment
CMS CMS

5. Sites using AEM
aws.amazon.com chase.com telegraph.co.uk
cisco.comnike.comsalesforce.com intel.com

6. Sling/REST concepts
● Anything can be a resource
● Resources are independent from their representation
● A resource is identified by URL
● URLs have an implicit hierarchy
● Methods perform Operations on resources
● HTTP status codes are used to indicate result success
● Safe methods shouldn‘t change anything
● Idempotent methods shouldn‘t change anything beyond their first execution

7. The difference (JEE/Spring MVC vs Sling)
@RestController
@Service
@Repository
DB Schema
DB data scripts
JEE stack

8. The difference (JEE/Spring MVC vs Sling)
@RestController
@Service
@Repository
DB Schema
DB data scripts Resources
JEE stack Apache Sling
@SlingServlet
Scripts

9. The difference (JEE/Spring MVC vs Sling)
JEE stack:
Use different URLs &
controllers for different
representation of the
same resource
@RestController1
@RestController2
@RestController3

10. Sling Architecture
Sling engine
JCR repository
(apache jackrabbit/oak)
OSGi framework
(Apache Felix)
HTTP ● Jetty process http requests
● Sling does URL decomposition, resource
and script resolution
● OSGi manage bundles and provide system
services to bundles (sling and jackrabbit
are bundles inside OSGi container)
● JCR stores content
Sling launchpad

11. What is JCR
● API to access content repositories in a uniform manner
● Everything is content
● Kind of NoSQL (tree of nodes and properties)
● Covered by JSR-170 (Version 1), and by JSR-283 (version 2)
● Major implementation is Apache Jackrabbit

12. What is JCR: how it looks
{
"jcr:primaryType": "sling:Folder",
"jcr:createdBy": "admin",
"jcr:created": "Sun Oct 09 2016 21:37:57 GMT+0300",
"private": {
"jcr:primaryType": "nt:unstructured",
"confirmed": {
"jcr:primaryType": "nt:unstructured",
"jcr:title": "Confirmed orders",
"sling:resourceType": "slingbucks/confirmed",
"703bed1112ac94c2b446787a6c5096bb": {
"jcr:primaryType": "nt:unstructured",
"opt_cup": "plastic",
"opt_coffeetype": "espresso",
"orderConfirmed": "Confirm this order",
"opt_size": "small",
"customerName": "Anonymous Coffee Drinker",
"sling:resourceType": "slingbucks/order",
"opt_sugar": "white",
"lastModified": "Sun Oct 09 2016 21:40:38 GMT+0300"
},
}
},
....

13. Sling request handling
URL decomposition Script resolution Script execution
Break down url into:
● Resource path
● Selectors
● Extension
● Suffix
● Use sling resourceType to
locate script’s path
● Use selectors and
extension to locate script
name
Scripts that render resource
as text (html/json/xml/etc) or
create/modify resource

14. Sling URL decomposition
/content/slingbucks/public/orders.tidy.json/last
Resource path
● The substring of the request URL before
the first dot (.)
● Mandatory
Selector
● Substring between 1st dot, and the dot leading the extension
● Used for alt. methods of rendering the content
● Multiple selectors may be used (separated by . )
● Optional
Extension
● The string between the last dot after the resource path and
the next slash
● Specifies the content format
● Optional
Suffix
● Path starting with the slash up to the end of
the request URL
● At least a dot must be in the URL to let Sling
detect the suffix path
● Can be used to provide additional information
for the processing script

15. Sling script resolution: servlets
@SlingServlet(
resourceTypes = "slingbucks/order",
extensions = {"txt"},
methods = "GET"
)
public class SlingSampleServlet extends SlingSafeMethodsServlet {
@Override
protected void doGet(SlingHttpServletRequest request, SlingHttpServletResponse response)
throws ServletException, IOException {
Resource r = request.getResource();
String value =r.adaptTo(ValueMap.class).get("customerName", String.class);
response.getWriter().append(value);
}
}

16. Sling: script name resolution
/content/slingbucks/order
/content
slingbacks
order
slingResourcetype = slingbucks/order
/app
slingbucks
order
order.jsp
txt.jsp
….
/libs
...

17. Sling script name resolution

18. Sling scripts
● Sling supports JSR 223 (Scripting for the Java Platform), so any programming
languages may be supported
● Sling has build-in support for ECMAScript, JSP and Java (via servlets/OSGi
service)

19. Sling scripts
<html>
<head>
<title><%= currentNode["jcr:title"] %></title>
<% load("../common/head.esp"); %>
</head>
<body>
<h1><%= currentNode["jcr:title"] %></h1>
<%
var childNodes = currentNode.getChildren();
for(i in childNodes) {
sling.include(childNodes[i].path, "replaceSelectors=backoffice");
}
%>
</body>
</html>

20. Sling concepts: adaptTo
Response = f (Request)

21. Sling concepts: adaptTo
public interface Adaptable {
/**
* Adapts the adaptable to another type.
*
*/
<AdapterType> AdapterType adaptTo(Class<AdapterType> type);
}
@Override
protected void doGet(SlingHttpServletRequest request, SlingHttpServletResponse response) throws
ServletException, IOException {
MyResponse myResponse = request.adaptTo(MyResponse.class);
response.getWriter().append(myResponse.toJson());
}

22. Sling concepts: adaptTo
@Component
@Service(value=org.apache.sling.api.adapter.AdapterFactory.class)
@Properties({
@Property(name = "adaptables", value = { "org.apache.sling.api.SlingHttpServletRequest" }),
@Property(name = "adapters", value = { "sling.sample.MyResponse" })
})
public class MyResponseProvider implements AdapterFactory {
@Override
public <AdapterType> AdapterType getAdapter(Object adaptable, Class<AdapterType> type) {
return (AdapterType) (MyResponse) …..;
}
}

23. Summary
Good
● Provide ability to “touch” resources
● Encourage to design resources
● Everything out of the box (more like platform
rather than framework)
Not good
● Too little available information
● No async support
● Development is relatively slow

24. The End
?