CQCON 2013: five Sling features you should know Olaf Otto

19.06.2013

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1: Write custom tag libraries

<taglib version="2.0" xmlns="http://java.sun.com/xml/ns/j2ee" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xsi:schemaLocation="http://java.sun.com/xml/ns/j2ee http://java.sun.com/xml/ns/j2ee/web-jsptaglibrary_2_0.xsd"> <taglib> <uri>http://www.corp.com/taglibs/mytaglib/1.0</uri> ... </taglib>

META-INF/<name>.tld

Version

your API!

Fully

qualified

identifier

Use current

XSD

Taglibs are not exactly the

latest trend, but they get

the job done properly – re-

usable, testable

implementations for view-

related tasks such as rich

text transformation, i18n,

date formatting etc.

Multiple TLDs

allowed

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1.1 Talking of versioned taglibs:

<sling:include /> <sling:forward /> <sling:defineObjects />

http://sling.apache.org/taglibs/sling/1.0

<sling:call /> <sling:eval />

http://sling.apache.org/taglibs/sling/1.2

Current

${sling:adaptTo(from, to)} ${sling:findResources(resolver, query, language)} ${sling:getRelativeResource(resource, path)} ${sling:getResource(resolver, path)} ${sling:listChildren(resource)} <sling:getProperty /> <sling:getResource />

http://sling.apache.org/taglibs/sling/1.3

Coming

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2: Enriching the view

@Service

@Component(immediate = true)

public class Provider implements BindingsValuesProvider {

@Override

public void addBindings(Bindings bindings) {

}

}

View (JSP) anything

Map<String, ?>

${bindings.key}

The BindingsValuesProvider allows you to inject

anything into any view and thus aides in de-

coupling view and backend layer.

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2.1 By the way: Semantic Annotations

@SlingServlet(paths = "/bin/myservlet")

public class MyServlet extends SlingSafeMethodsServlet

{

@Override

public void doGet(…) {

}

}

@SlingFilter

public class MyFilter implements Filter {

@Override

public void doFilter(…) {

}

}

Use typesafe Java 5 annotations

(not the JAVADoc ones). SlingFilter

and SlingServlet are part of felix-scr-

annotations and supported by the

maven-scr-plugin.

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Click to edit Master title style ++complexity

Sling has a simple generic resource

model (Resource, ValueMap), which

may not suffice when resources

require complex operations on their

data…

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3: When Resource is not enough

CUG

protection

Persistence

Sitemap

entry

Page cq:Page

Properties

Link

These are independent

aspects of the cq:Page

resource type taken from

an actual project. Each

aspect requires an

implementation.

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3.1 .adaptTo(TheRescue)

No more util-class projects, please.

{data, Operations} : Model

.adaptTo(X)

Best pratice for Sling: write a POJO for an aspect and

.adaptTo it.

.adaptTo’s most valueable application is adaptation to

type safe representations of aspects of resources

Please do not implement such aspects

in static util functions. This is a terrible

anti-pattern.

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3.2: .adaptTo & OSGi best practices

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Implementation API

Feature

.adaptTo

Provides API

implementation +

AdapterFactory

Clean

separation

.adapTo is a perfect match for OSGi best practices. Refer to

http://www.ibm.com/developerworks/websphere/techjournal/1007_charters/1007_charter

s.html#sec5

Contains

adapter

interface

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3.3: Boilerplate, anyone?

@Component

@Service

@Properties({

@Property(name = "adaptables",

value = "org.apache.sling.api.resource.Resource"),

@Property(name = "adapters",

value = "fully.qualified.type.Name")

})

public class MyFactory implements AdapterFactory {

public <T> T getAdapter(Object from, Class<T> toType) {

…

}

}

= from

= to

If () else if () …

Stringly typed

Such boilerplate may well be

the reason developers avoid

adapter factories

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3.4: Choices!

Generic Adapterfactory

Improve declaration

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Luckily, boilerplate can be

circumvented by either

simplifying declaration or

programmatically publishing

a generic adapter factory

Note: AdapterFactories are

excellent extension points for

Spring integration. When

obtaining the Adapter from

the Spring bean factory, you

can transparently adapt to a

Spring bean at any time

from anywhere in you

application.

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3.5 Custom SCR annotation for adapter factories

@Adapts(from = Resource.class, to = Name.class)

public class MyFactory implements AdapterFactory {

public <T> T getAdapter(Object from, Class<T> toType) {

…

}

}

How? SCR plugin / task + AnnotationProcessor

Typesafe!

The simple most approach is to

exchange the boilerplate SCR

metadata with a semantic

annotation

Refer to: http://felix.apache.org/documentation/subprojects/apache-felix-

maven-scr-plugin/extending-scr-annotations.html

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4: Decorating resources

• Manipulation of any Resource

• Transparent (.adaptTo, Views)

@Service

@Component(immediate = true)

public class Decorator implements ResourceDecorator {

@Override

public Resource decorate(Resource resource) {

}

} Note: This is one of the most powerful

extension points allowing manipulating

any resource – even script and servlets

(everything is a resource!).

Sample application: Resources with a specific property (e.g. inherit=true) are wrapped

with a resource that provides an InhertianceVauleMap. This way, you can enable

transparent inheritance for any resource at any time without changing a single line of

code. Source from CQCON, see: http://www.cqcon.eu/2013/en/speakers/olaf-otto.html

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5: Providing custom resources

ResourceProvider /custom

/custom/<child>

JCR

/content

/site

Refer to http://sling.apache.org/documentation/the-sling-

engine/resources.html , «Providing Resources»

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• Bad fit for thirdparty integration (tight coupling!). Better:

• Good fit for local integration (DBs, Filesystem…). Upcoming Sling version features

provider for MongoDB.

5.1: The pros an cons

soaml ESB

AdvertiseAdvertiseAdvertise UseUseUse

Enterprise serv ice bus

AdvertiseAdvertise UseUse

System

System

System Client

Client

Client

RESTful support –

e.g. ServiceMix

JSONP for cross-

domain integration

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• CRUD support with PersistableValueMap

• Deployment of custom node types in bundles (CND)

• Static resource support: Serve static resource from bundles

Some more things to take a look at:

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