Apache Sling is an innovative web framework built on top of the Java Content Repository (JCR), that uses OSGi for its component model and fosters RESTful application design. This presentation will showcase how the Apache Sling framework can be used to build a unified REST-based middleware for multiple data sources, such as MongoDB, Apache Cassandra, Apache Jackrabbit Oak or classical relational databases. In doing so it will present the benefits that come from a single Resource API over multiple data stores, both at the library level and at the HTTP boundary.

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Apache Sling as an OSGi-powered
REST middleware
Robert Munteanu, Adobe Systems Inc

2. #Devoxx #Sling @rombert
Getting to know each other
$DAYJOB

Adobe Experience
Manager
 Apache Sling
 Apache Jackrabbit
 Apache Felix
FOSS

Apache Sling

MantisBT

Mylyn Connector for MantisBT

Mylyn Connector for Review Board

3. #Devoxx #Sling @rombert
Agenda
● What is Apache Sling?
● Meet Barry
● Demo 1
● Why use Sling as a RESTful middleware?
● Demo 2
● What else is there to Sling?

4. #Devoxx #Sling @rombert
Apache Sling - History
2007
Incubation
2009
TLP
2015
Version 8
200x
Pre-Apache

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High-level View of the Code
Source: OpenHub

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Level of activity
Source: OpenHub
Source: status.apache.org

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Conceptual foundations
REST-based
Content-driven
OSGi-powered
Scripting InsideApache

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REST-based
/content/blog/
/content/blog/{0}.html
/
BlogViewController
BlogListController
HomeController
SlingMainServlet
/
/content
/content/blog
/content/blog/hello-world

9. #Devoxx #Sling @rombert
REST-based
/
/content
/content/blog
/content/blog/hello-world
[sling/redirect]
[sling/redirect]
[ blog/welcome]
[ blog/page]

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Barry – Senior Buzzword Deliverer

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Demo time!

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How is everything mapped?
/ ( root )
/content/blog/comments
/content/blog/posts
/content/blog/images

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How does Sling manage this?
ResourceProvider
JCR NoSQL FS
Couchbase MongoDB
ResourceProviderFactory
Produces

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SPI → API
ResourceProviderFactory
OSGi Service Registry
ResourceResolver
Registers Gets

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How does my code get invoked?
1 GET /content/blog/posts/hello_world.json
2 ResourceResolver.resolve(...)
3 ServletResolver.resolveServlet(...)
4 servlet.doGet(...)

16. #Devoxx #Sling @rombert
Reading Resources
SELECT * FROM posts WHERE id = 83
rr.getResource(“/posts/hello_world”);

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Reading Resources
SELECT * FROM posts
WHERE parent_id = 25
LIMIT 10
for (Resource post :
resource.getChildren() ) {
// process first 10
}

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Reading Resources
SELECT * FROM posts
WHERE author = “john”
ORDER BY published DESC
rr.findResources(“//element(*,
blog:Posts)[@author='john'] ORDER BY
@published DESC”, “xpath”);

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Writing Resources
rr.create(parent, “new-blog-post”,
Map.of(“author”, “John”,
“title”, “New Blog Post”));
rr.delete(resource);
rr.commit();

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How do I handle requests?
@SlingServlet(methods="POST", extensions="comments",
resourceTypes=SlingshotConstants.RESOURCETYPE_ITEM)
public class CommentPostServlet
extends SlingAllMethodsServlet {
protected void doPost(final SlingHttpServletRequest
request, final SlingHttpServletResponse response) {
/* implementation */
}
}

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Reading data
Resource res = request.getResource();
// 1. reading ...
ValueMap properties = ↵
res.getValueMap();
String title = properties.get(“jcr:title”,↵
“Missing”);
Post post = res.adaptTo(Post.class);
title = post.getTitle();

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Why do we need adaptTo?
Adaptable
Resource ValueMap
Map<String,Object> Post

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Writing data
Resource res = request.getResource();
// 2. writing ...
ValueMap properties = ↵
res.adaptTo(ValueMap.class);
String title = properties.put(“jcr:title”,↵
“Hello, world”);
Post post = res.adaptTo(Post.class);
post.setTitle(“Hello, world”);
res.getResourceResolver().commit();

24. #Devoxx #Sling @rombert
A Sightly Template
<h1>${resource.valueMap['jcr:title'] || 'Blog'}</h1>
<div data-sly-resource="${'/content/blog/stats'
@resourceType='redis/stats'}"/>
<div data-sly-list.child="${resource.listChildren}">
<h2>${child.valueMap['jcr:title']}</h2>
<div data-sly-use.helper="${'welcome.js'
@text=child.valueMap['jcr:description'] }">
${helper.excerpt @ context='html'}
<a href="${child.path}.html">Read more</a>
</div>
</div>

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Demo time!

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Oh, but there's more

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More features
● Eventing, Thread Pooling, Job Management, Caching
● Scripting: Groovy, Scala, JSP, Sightly, Java, Ruby,
Thymeleaf
● Flexible resource rendering with resource types
● Very extensible due to being internally powered by OSGi –
most extension points available to clients

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Beyond the NoSQL datastores

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Buzzword checklist
✔ REST
✔ Middleware
✔ NoSQL
✔ OSGi

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Resources
● Apache Sling – http://sling.apache.org
● Sling NoSQL providers -
http://sling.apache.org/documentation/bundles/nosql-res
ource-providers.html
● Apache Jackrabbit Oak -
http://jackrabbit.apache.org/oak/