Getting Started with AEM Sites Chapter 6 - Creating a new AEM Component

This is Chapter 6 of a multi-part tutorial. Chapter 5 can be found here and an overview can be found here.

You can check out the finished code on GitHub or you can download the solution package:

In this part of the WKND tutorial, a Byline Component is built to be used on the Article pages that displays authored information about the article's contributor.

The implementation of this new component includes a dialog that collects the byline content and a custom Sling Model dynamically retrieves the byline's

• Name
• Image
• Occupations

for display by a HTL script.

First, create the Byline component node structure and define a dialog. This represents the Component in AEM and implicitly defines the component's resource type by its location in the JCR.

The dialog exposes the interface with which content authors can provide. For this implementation, the AEM WCM Core Component's Image component will be leveraged to handle the authoring and rendering of the Byline's image, so it will be set as our component's sling:resourceSuperType.

This byline.html is revisited later in this part once the Sling Model is created. The HTL file's current state allows the component to display in the AEM Sites' Page Editor when it's drag and dropped onto the page.

Next, define a dialog for the Byline component with the following fields:

• Name: a text field the contributor's name.
• Image: a reference to the contributor's bio picture.
• Occupations: a list of occupations attributed to the contributor. Occupations should be sorted alphabetically in an ascending order (a to z).

Following the same approach as with the Dialog creation, create a Policy dialog (formerly known as a Design Dialog) to hide unwanted fields in the Policy configuration inherited from the Core Components' Image component.

Deploy the code to AEM.

We'll add the Byline component in its current state to an Article page to verify that the node definition is correct, AEM sees the new component definition and the component's dialog works for authoring.

 AEM authors configure and author components via the dialogs.  At this point in the development of the Byline component the dialogs are included for collecting the data, however the logic to render the authored content has not yet been added.

Next, we'll create a Sling Model to act as the data model and house the business logic for the Byline component.

Sling Models are annotation driven Java "POJO's" (Plain Old Java Objects) that facilitate the mapping of data from the JCR to Java variables, and provide a number of other nicities when developing in the context of AEM.

In order to most efficiently use Sling Models, the project's POM's need updating. Update the reactor and core pom.xml files to use the latest standards and practices. We'll also use the opportunity to leverage the Apache Commons-Lang3 library which is provided by AEM and provides a suite of very useful utility classes.

Next, create a public Java Interface for the Byline. Byline.java defines the public methods needed to drive the byline.html HTL script.

BylineImpl.java is the implementation of the Sling Model that implements the Byline.java interface defined earlier. The full code for BylineImpl.java can be found at the bottom of this section.

The first method we'll tackle is getName() which simply returns the value stored to the byline's JCR content node under the property name.

For this, the @ValueMapValue Sling Model annotation can be used to inject the value into a Java field in the Sling Model.

Because the JCR property shares the same name as the Java field (both are "name"), @ValueMapValue automatically resolves this association and injects the value at the property name into the Java field.

If the JCR property had been named something different, additional annotations can be used to coerce the value injection. For example, if the JCR property had been named fullName, the following would inject its value into the Java field name.

The next method to implement is getOccupations()` This method should collect all the occupations stored in the JCR property occupations and return a sorted (alphabetically) collection of them.

Using the same technique explored in getName() the property value can be injected into the Sling Model.

Now that the JCR property values are available in the Sling Model via the injected Java field occupations, the sorting business logic can be applied in the getOccupations() method.

The last public method is isEmpty() which determines when the component should consider itself "authored enough" to render.

For this component, we have business requirements stating that all three fields, name, image and occupations must be filled out.

Checking the name and occupation conditions are trivial (and the Apache Commons Lang3 provides the always handy StringUtils class), however, there is a problem in that it's unclear how the presence of the Image can be validated since we're using the Core Components Image component to surface the image.

There are two ways to tackle this:

1. Check if the fileReference JCR property resolves to an asset.

OR

2. Convert this resource into a Core Component Image Sling Model and ensure the getSrc() method is not empty.

We will opt for approach #2. The first approach is likely sufficient, but in this tutorial, the latter will be used to explore other features of Sling Models.

The first thing to do is create a private method that gets the Image. This method is left private because we do not need to expose the Image object in the HTL itself, and its only used to drive isEmpty().

There are two approaches to get the Image Sling Model:

1.  Use the @Self annotation, to automatically adapt the current request to the Image.class
  @Self
  private  Image image;

OR

2.  Use the Apache Sling ModelFactory OSGi service, which is a very handy service, and helps us create Sling Models of other types in Java code.

We will opt for approach #2.

Since Sling Models are Java POJO's, and not OSGi Services, the usual OSGi injection annotations, like @Reference, cannot be used, meaning the following would not work (modelFactory would be null).

Instead, Sling Models provide a special @OSGiService annotation that provides similar functionality.

With the ModelFactory available, a Core Component Image Sling Model can be created using modelFactory.getModelFromWrappedRequest(SlingHttpServletRequest request, Resource resource, java.lang.Class<T> targetClass), however, this method requires both a request and resource, neither yet available in the Sling Model.

For this, more Sling Model annotations are used!

To get the current request the @Self annotation be used to inject the adaptable (which is defined in the @Model(..) as SlingHttpServletRequest.class, into a Java class field.

Remember, using @Self Image image to inject the Core Component Image Sling Model was an option above - the @Self annotation tries to inject the adaptable object (in our case a SlingHttpServletRequest), and adapt to the annotation field type. Since the Core Component Image Sling Model is adaptable from SlingHttpServletRequest objects, this would have worked and is less code than our more exploratory approach.

Now we've injected the variables necessary to instantiate our Image model via the ModelFactory API. We will use Sling Model's @PostConstruct annotation to obtain this object after the Sling Model instantiates.

@PostConstruct is incredibly useful and acts in a similar capacity as a constructor, however, it is invoked after the class is instantiated and all annotated Java fields are injected. Whereas other Sling Model annotations annotate Java class fields (variables), @PostConstruct annotates a void, zero parameter method, typically named init() (but can be named anything).

Remember, Sling Models are NOT OSGi Services, so it is safe to maintain class state. Often the @PostConstruct derives and sets up Sling Model class state for later use, similar to what a plain constructor does.

Note that if the @PostConstruct method throws an exception, the Sling Model will not instantiate (it will be null).

getImage() can now be updated to simply return the image object.

Let's head back to isEmpty() and finish the implementation.

Note multiple calls to getImage() is not problematic as returns the initialized image class variable and does not invoke modelFactory.getModelFromWrappedRequest(...) which isn't an incredibly costly, but worth avoiding calling unnecessarily.

The final BylineImpl.java should look like:

In the ui.apps module, open /apps/wknd/components/content/byline/byline.html we created in the earlier set up of the AEM Component.

Let's review what this HTL script does so far:

1. The placeholderTemplate points to Core Components' placeholder, which displays when the component is not fully configured. This renders in AEM Sites Page Editor as a grey box with the component title, as defined above in the cq:Component`'s jcr:title property.
2. The data-sly-call="${placeholderTemplate.placeholder @ isEmpty=false} loads the placeholderTemplate defined above and passes in a boolean value (currently hard-coded to false) into the placeholder template. When isEmpty is true, the placeholder template renders the grey box, else it renders nothing.

Update byline.html with the following skeletal HTML structure:

Note the CSS classes follow the BEM naming convention. While the use of BEM conventions isn't mandatory, BEM is recommended as it's used in Core Component CSS classes and generally results in clean, readable CSS rules.

The Use block statement is one of the most common, as it's used to instantiate Sling Model objects in the HTL script and assign it to an HTL variable.

data-sly-use.byline="com.adobe.aem.guides.wknd.components.Byline" uses the Byline interface (com.adobe.aem.guides.wknd.components.Byline) implemented by BylineImpl and adapts the current SlingHttpServletRequest to it, and the result is stored in a HTL variable name byline (data-sly-use.<variable-name>).

HTL borrows from JSTL, and uses the same shortening of Java getter methods names.

For example, invoking the Byline Sling Model's getName() method can be shortened to byline.name, similarly instead of byline.isEmpty, this can be shorted to byline.empty. Using full method names, byline.getName or byline.isEmpty, works as well. Note the () are never used to invoke methods in HTL (similar to JSTL).

Java methods that require a parameter cannot be used in HTL. This is by design to keep the logic in HTL simple.

The Byline name can be added to the component by invoking the getName() method on the Byline Sling Model, or in HTL: ${byline.name}.

HTL Expressions Options act as modifiers on content in HTL, and range from date-formatting to i18n translation. Expressions can also be used to join lists or arrays of values, which is what's needed to display the occupations in a comma delimited format.

Expressions are added via the @ operator in the HTL expression. To join the list of occupations with ", ", the following code is used:

Most HTL scripts for AEM Components leverage the placeholder paradigm to provide a visual cue to authors indicating a component is incorrectly authored and will not display on AEM Publish. The convention to drive this decision is to implement a method on the component's backing Sling Model, in our case: Byline.isEmpty().

isEmpty() is invoked on the Byline Sling Model and the result (or rather its negative, via the `!` operator) is saved to an HTL variable named hasContent:

Note the use of data-sly-test, the HTL test block is interesting in that it both sets an HTL variable AND renders/doesn't render the HTML element it's on, based on if the result of the HTL expression is truthy or not. If truthy, the HTML element renders, else it does not render.

This HTL variable hasContent can now be re-used to conditionally show/hide the placeholder.

The HTL script for byline.html is now almost complete and is only missing the image.

Since we use sling:resourceSuperTyped the Core Components Image component to provide the authoring of the image, we can also use the Core Component Image component to render the image!

For this, we need to include the current byline resource, but force the resource type of the Core Components Image component, using resource type core/wcm/components/image/v2/image. This can be a powerful pattern to re-use components in one another. For this HTL's data-sly-resource block is used.

This data-sly-resource, included the current resource via the relative path '.', and forces the inclusion with the resourceType of core/wcm/components/image/v2/image.

The Core Component resource type is used directly, and not via a proxy, because this is an in-script use, and it's never persisted to our content.

Completed byline.html below: 

Deploy the updated code to AEM.

After deploying the update, the image now appears and we have a un-styled, but working Byline component.

The AEM Web Console's Sling Models Status view displays all the registered Sling Models in AEM. The Byline Sling Model can be validated as being installed and recognized by reviewing this list.

If the BylineImpl was not displayed in this list, then there was is likely an issue with the Sling Model's annotations or with the SlingModelsScanner Module configuration in the core pom.xml.

The Byline component needs to be styled to align with the creative design for the Byline component. This will be achieved by using LESS, which AEM provides support for via its Client Libraries, to generate the necessary CSS to provide the correct default style for the Byline component.

After styling, the Byline component should adopt the follow aesthetic.

Add default styles for the Byline component. In the ui.apps project under /apps/wknd/clientlibs/clientlib-site/components.

Starting from this skeletal framework of the CSS class we are "allowed" to target makes writing clean CSS more straightforward, and reduces the temptation to style non-BEM CSS classes or bare elements.

Let's drop in the style implementations, and re-use the previously defined LESS variables from /apps/wknd/clientlibs/clientlib-site/site/less/variables.less.

Update /apps/wknd/clientlibs/clientlib-site/main.less to include byline.less.

Add an import statement to include byline.less beneath the other imports of component styles.

Deploy the code to AEM, clear the browser cache to ensure stale CSS is not being served, and refresh the page with the Byline component to get the full styled.

Below is what the fully authored and styled Byline component should look like on the AEM page.

Watch the video below for a quick walk-through of what was built in this part of the WKND tutorial.

If you get stuck or have additional questions make sure to check out the Experience League forums for AEM or view existing GitHub issues.

Didn't find what you were looking for? Think you found an error? Please file a GitHub issue for the WKND project.

Next part in the tutorial: 

• Getting Started with AEM Sites Chapter 7 - Teaser and Carousel Components 
• View the finished code on GitHub or download the finished package for this part of the tutorial:

Note if you do not see src/main/java source folder in Eclipse you can add the folders by right clicking src and adding folders for main and java. After adding the folders you should see the src/main/java package appear.

Note if you have unresolved package imports for some of the new dependencies added to the core project, try updating the wknd-sites-guide.core maven project. You can do this by right-clicking wknd-sites-guide.core > Maven > Update Project.