slingmodels

Sling Models in AEM
(by Ankur Chauhan)

Agenda
1. What are Sling Models?

Agenda
2. Why Sling Models?

Agenda
3. How to use Sling Models in AEM?

Agenda
4. Sling Model Annotations with Demo.

“Sling models are pure Plain Old Java Objects (POJO), which
are automatically mapped from Sling objects, typically
resource and request objects. We can also inject OSGi
Services in these models as well.”

➢
These are "Pure" POJOs.
➢
Use standard annotations where possible.
➢
OOTB, support resource properties (via ValueMap), SlingBindings, OSGi services,
request attributes
➢
Adapt multiple objects - minimal required Resource and SlingHttpServletRequest
➢
Client doesn't know/care that these objects are different than any other adapter
factory
➢
Support both classes and interfaces.
➢
Work with existing Sling infrastructure (i.e. not require changes to other bundles).
Design Goals

Agenda
4. Sling Model annotations with Demo.

➢
Using Sling Models you can do more with less code
➢
You can reduce your coding efforts.
➢
Your code is more maintable using Sling Modes.
➢
You don't have to write redundent code.
It is more understandable using a live scenario. (Native Ecommerce API in AEM)

Agenda
4. Sling Model annotations with Demo

Dependency Required
➢
If you are working with AEM6 then you have org.apache.sling.models.api package
already present in your AEM instance.

Dependency Required
➢
➢
If you are using earlier version of AEM then you have to download this package from
Sling website and then install it at your AEM instance.

Dependency Required
➢
➢
➢
You can find all the Sling Models Injectors at
http://localhost:4502/system/console/status-slingmodels

Dependency Required
➢
➢
➢
You can find all the Sling Models Injectors at
http://localhost:4502/system/console/status-slingmodels
➢
Maven dependecy for your project can be found at-

Dependency Required
➢
It depends on your AEM version so best way is to find this dependency at your on AEM instance
for that you can search for – org.apache.sling.models
in felix console bundles tab. Or
➢
Go to Felix Console packages tab And search for org.apache.sling.models.annotations.Model
it you will get the Maven dependency for your project.

Dependency Required
➢
It depends on your AEM version so best way is to find this dependency at your on AEM instance
for that you can search for – org.apache.sling.models
in felix console bundles tab. Or
➢
Go to Felix Console packages tab And search for org.apache.sling.models.annotations.Model
it you will get the Maven dependency for your project.
<dependency>
<groupId>org.apache.sling</groupId>
<artifactId>org.apache.sling.models.api</artifactId>
<version>1.0.0</version>
<scope>provided</scope>
</dependency>

➢
Now add this dependency to your project.
➢
Search for maven-scr-plugin in your parent pom.xml file.
➢
Update it with
<plugin>
<groupId>org.apache.felix</groupId>
<artifactId>maven-bundle-plugin</artifactId>
<extensions>true</extensions>
<configuration>
<instructions>
<Sling-Model-Packages> sling.models </Sling-Model-Packages>
<Bundle-Category>sling-model-demo</Bundle-Category>
</instructions>
</configuration>
</plugin>
➢
This plugin modification is mandatory so that this header must be added to the
bundle's manifest file.

Annotations
➢
@Model
➢
@Inject
➢
@Optional
➢
@Default
➢
@Named
➢
@PostConstruct
➢
@Via
➢
@Source
➢
@Required
➢
List<Resource> list.

Before starting with these annotations, Let's have a look on this line of code.
resource.adaptTo(ValueMap.class);
In this code snippet -
➢
resource will behaves as an adaptable
➢
ValueMap behaves as an adapter

Code Snippet Part - I
@Model(adaptables = Resource.class )
public class ResourceValues {
...
}

@Inject // If defined then Resource must have this property else it will return null.
private String firstName;
}

/* To provide default value to this string for Strings & primitives, Default only works with
@Inject annotation not with @Optional annotation. */
@Inject @Default(values="defaultValue")
private String lastName;
}

/* If the field or method name doesn't exactly match the property name */
@Inject @Named("secondPropertyName")
private String otherName;
}

/* If the field or method name doesn't exactly match the property name */
@Inject @Named("secondPropertyName")
private String otherName;
@Optional // If defined then Resource may or may not have property.
private String fullName;
}

Question?
Is it required to add this @optional annotation at every field, if want to make is optional?

Answer ?
Yes, if you are using Sling API version before 1.0.2 and after this version you get another property
in @Model annotation named as defaultInjectionStrategy. After adding this property all the fields
are by default @optional.
But if you wnat some field as required then you have to add @required annotation on that field.
This property is defined in @Model annotation and it's syntex is-
@Model(adaptables=Resource.class,defaultInjectionStrategy=DefaultInjectionStrategy.OPTIONAL)

Code Snippet Part - II
How to use Sling Models in AEM?
ResourceValues resourceValues = resource.adaptTo(ResourceValues.class)

How to use in JSP?
<sling:adaptTo adaptable="${resource}" adaptTo="org.apache.sling.models.it.models.MyModel"
var="model"/>

How to use in JSP?
<sling:adaptTo adaptable="${resource}" adaptTo="org.apache.sling.models.it.models.MyModel"
var="model"/>
How to use in Sightly?
${sling:adaptTo(resource, 'org.apache.sling.models.it.models.MyModel')}

Code Snippet Part - III
@Model(adaptables = Resource.class)
/* Child List injection works after Sling version 1.0.6.
This List injection will hold list of all the child nodes present under childs node under
current resource.
*/
@Inject
private List<Resource> childs;
}

Code Snippet Part - III
@Model(adaptables = Resource.class)
/* Child List injection works after Sling version 1.0.6.
This List injection will hold list of all the child nodes present under childs node under
current resource.
*/
@Inject
private List<Resource> childs;
/*
The @PostConstruct annotation can be used to add methods which
are invoked upon completion of all injections
*/
@PostConstruct
protected void sayHello() {
System.out.println("post construct is working");
}
}

Code Snippet Part - IV
@Model(adaptables=SlingHttpServletRequest.class)
public interface RequestValues {
/* will return
request.getResource().adaptTo(ValueMap.class).get("propertyName", String.class)
*/
@Inject @Via("resource")
String getPropertyName();
}
Means:-
“If the injection should be based on a JavaBean property of the adaptable, you can indicate this
using the @Via annotation”

Code Snippet Part - V
@Model(adaptables=SlingHttpServletRequest.class)
public interface RequestValues {
/* Ensure that "resource" is retrived from the bindings, not a request attribute */
@Inject @Source("script-bindings")
Resource getResource();
}

References:
Sling Model Documentation

slingmodels

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