Custom Component

This tutorial covers the end-to-end creation of a custom AEM Byline Component that displays content authored in a Dialog, and explores developing a Sling Model to encapsulate business logic that populates the component’s HTL.

Prerequisites

Review the required tooling and instructions for setting up a local development environment.

Starter Project

NOTE

If you have been following along in previous parts of the tutorial, you will notice that the Starter Project for this chapter accelerates the implementation. It includes a few more templates and much more content. As a bonus, feel free to explore the new content and other areas of the implementation, outside of the custom component development.

Check out the base-line code the tutorial builds on:

  1. Clone the github.com/adobe/aem-guides-wknd repository.

  2. Check out the custom-component/start branch

    $ git clone git@github.com:adobe/aem-guides-wknd.git ~/code/aem-guides-wknd
    $ cd ~/code/aem-guides-wknd
    $ git checkout custom-component/start
    
  3. Deploy code base to a local AEM instance using your Maven skills:

    $ cd ~/code/aem-guides-wknd
    $ mvn clean install -PautoInstallSinglePackage
    

You can always view the finished code on GitHub or check the code out locally by switching to the branch custom-component/solution.

Objective

  1. Understand how to build a custom AEM component
  2. Learn to encapsulate business logic with Sling Models
  3. Understand how to use a Sling Model from within an HTL Script

What you will build

In this part of the WKND tutorial, a Byline Component is created that will be used to displays authored information about an article’s contributor.

byline component example

Byline component visual design provided by WKND design team

The implementation of the Byline component includes a dialog that collects the byline content and a custom Sling Model that retrieves the byline’s:

  • Name
  • Image
  • Occupations

for display by a HTL script, which renders the HTML that the browser ultimately displays.

byline de-composition

Byline component decomposition

Create Byline component

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.

Create Component Node

  1. In the ui.apps module, navigate to /apps/wknd/components/content and create a new node named byline of type cq:Component.

    dialog to create node

  2. Add the following properties to the Byline component’s cq:Component node.

    jcr:title = Byline
    jcr:description = Displays a contributor's byline.
    componentGroup = WKND.Content
    sling:resourceSuperType =  core/wcm/components/image/v2/image
    

    Byline component properties

    Which results in this .content.xml XML:

    <?xml version="1.0" encoding="UTF-8"?>
    <jcr:root
        xmlns:sling="https://sling.apache.org/jcr/sling/1.0" xmlns:jcr="https://www.jcp.org/jcr/1.0"
        jcr:primaryType="cq:Component"
        jcr:title="Byline"
        jcr:description="Displays a contributor's byline."
        componentGroup="WKND.Content"
        sling:resourceSuperType="core/wcm/components/image/v2/image"/>
    

Create the HTL script

  1. Beneath the byline node, add a new file byline.html, which is responsible for the HTML presentation of the component. Naming the file the same as the cq:Component node is important as it becomes the default script Sling will use to render this resource type.

  2. Add the following code to the byline.html.

    <!--/* byline.html */-->
    <div data-sly-use.placeholderTemplate="core/wcm/components/commons/v1/templates.html">
    </div>
    <sly data-sly-call="${placeholderTemplate.placeholder @ isEmpty=true}"></sly>
    
    

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

Create the Dialog definition

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).
  1. Beneath the byline component node create a new node named cq:dialog of type nt:unstructured.

  2. Update the cq:dialog with the following XML. It is easiest to open up the .content.xml and copy/paste the following XML into it.

    <?xml version="1.0" encoding="UTF-8"?>
    <jcr:root xmlns:sling="http://sling.apache.org/jcr/sling/1.0" xmlns:jcr="http://www.jcp.org/jcr/1.0"
            xmlns:nt="http://www.jcp.org/jcr/nt/1.0"
            jcr:primaryType="nt:unstructured"
            jcr:title="Byline"
            sling:resourceType="cq/gui/components/authoring/dialog">
        <content
                jcr:primaryType="nt:unstructured"
                sling:resourceType="granite/ui/components/coral/foundation/container">
            <items jcr:primaryType="nt:unstructured">
                <tabs
                        jcr:primaryType="nt:unstructured"
                        sling:resourceType="granite/ui/components/coral/foundation/tabs"
                        maximized="{Boolean}false">
                    <items jcr:primaryType="nt:unstructured">
                        <asset
                                jcr:primaryType="nt:unstructured"
                                sling:hideResource="{Boolean}false"/>
                        <metadata
                                jcr:primaryType="nt:unstructured"
                                sling:hideResource="{Boolean}true"/>
                        <properties
                                jcr:primaryType="nt:unstructured"
                                jcr:title="Properties"
                                sling:resourceType="granite/ui/components/coral/foundation/container"
                                margin="{Boolean}true">
                            <items jcr:primaryType="nt:unstructured">
                                <columns
                                        jcr:primaryType="nt:unstructured"
                                        sling:resourceType="granite/ui/components/coral/foundation/fixedcolumns"
                                        margin="{Boolean}true">
                                    <items jcr:primaryType="nt:unstructured">
                                        <column
                                                jcr:primaryType="nt:unstructured"
                                                sling:resourceType="granite/ui/components/coral/foundation/container">
                                            <items jcr:primaryType="nt:unstructured">
                                                <name
                                                        jcr:primaryType="nt:unstructured"
                                                        sling:resourceType="granite/ui/components/coral/foundation/form/textfield"
                                                        emptyText="Enter the contributor's name to display."
                                                        fieldDescription="The contributor's name to display."
                                                        fieldLabel="Name"
                                                        name="./name"
                                                        required="{Boolean}true"/>
                                                <occupations
                                                        jcr:primaryType="nt:unstructured"
                                                        sling:resourceType="granite/ui/components/coral/foundation/form/multifield"
                                                        fieldDescription="A list of the contributor's occupations."
                                                        fieldLabel="Occupations"
                                                        required="{Boolean}false">
                                                    <field
                                                            jcr:primaryType="nt:unstructured"
                                                            sling:resourceType="granite/ui/components/coral/foundation/form/textfield"
                                                            emptyText="Enter an occupation"
                                                            name="./occupations"/>
                                                </occupations>
                                            </items>
                                        </column>
                                    </items>
                                </columns>
                            </items>
                        </properties>
                    </items>
                </tabs>
            </items>
        </content>
    </jcr:root>
    

    These node definitions use Sling Resource Merger to control which dialog tabs are inherited from the sling:resourceSuperType component, in this case the Core Components’ Image component.

    completed dialog for byline

Create the Policy dialog

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.

  1. Beneath the byline cq:Component node, create a new node named cq:design_dialog of type nt:unstructured.

  2. Update the cq:design_dialog with the following XML. It is easiest to open up the .content.xml and copy/paste the XML below into it.

    <?xml version="1.0" encoding="UTF-8"?>
    <jcr:root xmlns:sling="http://sling.apache.org/jcr/sling/1.0" xmlns:granite="http://www.adobe.com/jcr/granite/1.0" xmlns:cq="http://www.day.com/jcr/cq/1.0" xmlns:jcr="http://www.jcp.org/jcr/1.0" xmlns:nt="http://www.jcp.org/jcr/nt/1.0"
        jcr:primaryType="nt:unstructured"
        jcr:title="Byline"
        sling:resourceType="cq/gui/components/authoring/dialog">
        <content
                jcr:primaryType="nt:unstructured">
            <items jcr:primaryType="nt:unstructured">
                <tabs
                        jcr:primaryType="nt:unstructured">
                    <items jcr:primaryType="nt:unstructured">
                        <properties
                                jcr:primaryType="nt:unstructured">
                            <items jcr:primaryType="nt:unstructured">
                                <content
                                        jcr:primaryType="nt:unstructured">
                                    <items jcr:primaryType="nt:unstructured">
                                        <decorative
                                                jcr:primaryType="nt:unstructured"
                                                sling:hideResource="{Boolean}true"/>
                                        <altValueFromDAM
                                                jcr:primaryType="nt:unstructured"
                                                sling:hideResource="{Boolean}true"/>
                                        <titleValueFromDAM
                                                jcr:primaryType="nt:unstructured"
                                                sling:hideResource="{Boolean}true"/>
                                        <displayCaptionPopup
                                                jcr:primaryType="nt:unstructured"
                                                sling:hideResource="{Boolean}true"/>
                                        <disableUuidTracking
                                                jcr:primaryType="nt:unstructured"
                                                sling:hideResource="{Boolean}true"/>
                                    </items>
                                </content>
                            </items>
                        </properties>
                        <features
                                jcr:primaryType="nt:unstructured">
                            <items jcr:primaryType="nt:unstructured">
                                <content
                                        jcr:primaryType="nt:unstructured">
                                    <items jcr:primaryType="nt:unstructured">
                                        <accordion
                                                jcr:primaryType="nt:unstructured">
                                            <items jcr:primaryType="nt:unstructured">
                                                <orientation
                                                        jcr:primaryType="nt:unstructured"
                                                        sling:hideResource="{Boolean}true"/>
                                                <crop
                                                        jcr:primaryType="nt:unstructured"
                                                        sling:hideResource="{Boolean}true"/>
                                            </items>
                                        </accordion>
                                    </items>
                                </content>
                            </items>
                        </features>
                    </items>
                </tabs>
            </items>
        </content>
    </jcr:root>
    

    The basis for the preceding Policy dialog XML was obtained from the Core Components Image component.

    Like in the Dialog configuration, Sling Resource Merger is used to hide irrelevant fields that are otherwise inherited from the sling:resourceSuperType, as seen by the node definitions with sling:hideResource="{Boolean}true" property.

Deploy the code

  1. Deploy the updated code base to a local AEM instance using your Maven skills:

    $ cd ~/code/aem-guides-wknd
    $ mvn clean install -PautoInstallPackage
    

Add the component to a page

To keep things simple and focused on AEM component development, we’ll add the Byline component in its current state to an Article page to verify the cq:Component node definition is deployed and correct, AEM recognizes the new component definition and the component’s dialog works for authoring.

Because we added the Byline component to the WKND.Content Component Group, via the /apps/wknd/components/content/byline@componentGroup=WKND.Content property, it is automatically available to any Layout Container whose Policy allows the WKND.Content component group, which the Article Page’s Layout Container is.

Drag and drop the component onto the page

  1. Edit the article page at AEM > Sites > WKND Site > Language Master > English > Magazine > Ultimate Guide to LA Skateparks.

  2. From the left sidebar, drag and drop a Byline component on to bottom of the Layout Container of the opened article page.

    add byline component to page

Author the component

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.

  1. Ensure the left sidebar is open and visible, and the Asset Finder is selected.

    open asset finder

  2. Select the Byline component placeholder, which in turn displays the action bar and tap the wrench icon to open the dialog.

    component action bar

  3. With the dialog open, and the first tab (Asset) active, open the left sidebar, and from the asset finder, drag an image into the Image drop-zone. Search for “stacey” to find Stacey Roswells bio picture provided in the WKND ui.content package.

    stacey-roswells.jpg

    add image to dialog

  4. After adding an image, click on the Properties tab to enter the Name and Occupations.

    When entering occupations, enter them in reverse alphabetical order so the alphabetizing business logic we’ll implement in the Sling Model is readily apparent.

    Tap the Done button in the bottom right to save the changes.

    populate properties of byline component

  5. After saving the dialog, navigate to CRXDE Lite and review how the component’s content is stored on the byline component content node under the AEM page.

    Find the Byline component content node beneath the jcr:content/root/responsivegrid/responsivegrid node i.e /content/wknd/language-masters/en/magazine/guide-la-skateparks/jcr:content/root/responsivegrid/responsivegrid/byline.

    Notice the property names name, occupations, and fileReference are stored on the byline node.

    Also, notice the sling:resourceType of the node is set to wknd/components/content/byline which is what binds this content node to the Byline component implementation.

    byline properties in CRXDE

    /content/wknd/language-masters/en/magazine/guide-la-skateparks/jcr:content/root/responsivegrid/responsivegrid/byline

Create Byline Sling Model

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 niceties when developing in the context of AEM.

Review Maven Dependencies

The Byline Sling Model will rely on several Java APIs provided by AEM. These APIs are made available via the dependencies listed in the core module’s POM file.

  1. Open the pom.xml file beneath <src>/aem-guides-wknd/core/pom.xml.

  2. Find the dependency for the uber-jar in the dependencies section of the pom file:

    ...
        <dependency>
            <groupId>com.adobe.aem</groupId>
            <artifactId>uber-jar</artifactId>
            <classifier>apis</classifier>
        </dependency>
    ...
    

    The uber-jar contains all public Java APIs exposed by AEM. Notice that a version is not specified in the core/pom.xml file. The version is instead maintained in the Parent reactor pom located at the root of the project aem-guides-wknd/pom.xml.

  3. Find the dependency for core.wcm.components.core:

     <!-- Core Component Dependency -->
        <dependency>
            <groupId>com.adobe.cq</groupId>
            <artifactId>core.wcm.components.core</artifactId>
        </dependency>
    

    This is the all of the public Java APIs exposed by AEM Core Components. AEM Core Components is a project maintained outside of AEM and therefore has a separate release cycle. For this reason it is a dependency that needs to included separately and is not included with the uber-jar.

    Like the uber-jar, the version for this dependency is maintained in the Parent reactor pom file located at aem-guides-wknd/pom.xml.

    Later in this tutorial we will use the Core Component Image class to display the image in the Byline component. It is necessary to have the Core Component dependency in order to build and compile our Sling Model.

Byline interface

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

  1. Within the aem-guides-wknd.core module beneath src/main/java, create a new Java Interface named Byline.java by right-clicking the com.adobe.aem.guides.wknd.core.models package > New > Interface. Enter Byline as the interface Name, and click Finish.

    create byline interface

  2. Update Byline.java with the following methods:

    package com.adobe.aem.guides.wknd.core.models;
    
    import java.util.List;
    
    /**
    * Represents the Byline AEM Component for the WKND Site project.
    **/
    public interface Byline {
        /***
        * @return a string to display as the name.
        */
        String getName();
    
        /***
        * Occupations are to be sorted alphabetically in a descending order.
        *
        * @return a list of occupations.
        */
        List<String> getOccupations();
    
        /***
        * @return a boolean if the component has enough content to display.
        */
        boolean isEmpty();
    }
    

    The first two methods expose the values for the name and occupations for the Byline component.

    The isEmpty() method is used to determine if the component has any content to render or if it is waiting to be configured.

    Notice there is no method for the Image; we’ll take a look at as to why that is later.

Byline implementation

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.

  1. Within the core module beneath src/main/java, create a new class file named BylineImpl.java by right-clicking the com.adobe.aem.guides.wknd.core.models.impl package and selecting New > Class.

    For the name, enter BylineImpl. Add the Byline interface as an implementing interface.

    create byline implementation

  2. Open BylineImpl.java. It is auto-populated with all of the methods defined in the interface Byline.java. Add the Sling Model annotations by updating BylineImpl.java with the following class-level annotations. This @Model(..)annotation is what turns the class into a Sling Model.

    import org.apache.sling.api.SlingHttpServletRequest;
    import org.apache.sling.models.annotations.Model;
    import org.apache.sling.models.annotations.DefaultInjectionStrategy;
    ...
    @Model(
            adaptables = {SlingHttpServletRequest.class},
            adapters = {Byline.class},
            resourceType = {BylineImpl.RESOURCE_TYPE},
            defaultInjectionStrategy = DefaultInjectionStrategy.OPTIONAL
    )
    public class BylineImpl implements Byline {
        protected static final String RESOURCE_TYPE = "wknd/components/content/byline";
        ...
    }
    

    Let’s review this annotation and its parameters:

    • The @Model annotation registers BylineImpl as a Sling Model when it is deployed to AEM.
    • The adaptables parameter specifies that this model can be adapted by the request.
    • The adapters parameter allows the implementation class to be registered under the Byline interface. This allows the HTL script to call the Sling Model via the interface (instead of the impl directly). More details about adapters can be found here.
    • The resourceType points to the Byline component resource type (created earlier) and helps to resolve the correct model if there are multiple implementations. More details about associating a model class with a resource type can be found here.

Implementing the Sling Model methods

getName()

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 is used to inject the value into a Java field using the Request’s resource’s ValueMap.

...
import org.apache.sling.models.annotations.injectorspecific.ValueMapValue;
...
public class BylineImpl implements Byline {
    ...

    @ValueMapValue
    private String name;

    ...
    @Override
    public String getName() {
        return name;
    }
    ...
}

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

getOccupations()

The next method to implement is getOccupations(). This method collects 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’s field.

Once 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.

import java.util.ArrayList;
import java.util.Collections;
...

public class BylineImpl implements Byline {
    ...
    @ValueMapValue
    private List<String> occupations;
    ...
    public List<String> getOccupations() {
        if (occupations != null) {
            Collections.sort(occupations);
            return new ArrayList<String>(occupations);
        } else {
            return Collections.emptyList();
        }
    }
    ...
}
...

isEmpty()

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 before the component can be rendered.

import org.apache.commons.lang3.StringUtils;
...
public class BylineImpl implements Byline {
    ...
    @Override
    public boolean isEmpty() {
        if (StringUtils.isBlank(name)) {
            // Name is missing, but required
            return true;
        } else if (occupations == null || occupations.isEmpty()) {
            // At least one occupation is required
            return true;
        } else if (/* image is not null, logic to be determined */) {
            // A valid image is required
            return true;
        } else {
            // Everything is populated, so this component is not considered empty
            return false;
        }
    }
    ...
}

Tackling the “Image problem”

Checking the name and occupation conditions are trivial (and the Apache Commons Lang3 provides the always handy StringUtils class), however, it’s unclear how the presence of the Image can be validated since the Core Components Image component is used to surface the image.

There are two ways to tackle this:

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

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

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

  3. 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().

    The following private method for getImage():

    import com.adobe.cq.wcm.core.components.models.Image;
    ...
    private Image getImage() {
        Image image = null;
        // Figure out how to populate the image variable!
        return image;
    }
    

    As noted above, there are two more approaches to get the Image Sling Model:

    The first uses the @Self annotation, to automatically adapt the current request to the Core Component’s Image.class

    
    @Self
    private Image image;
    
    

    The second uses 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 the second approach.

    NOTE

    In a real-world implementation, approach “One”, using @Self is preferred since it’s the simpler, more elegant solution. In this tutorial we’ll use the second approach, as it requires us to explore more facets of Sling Models that are extremely useful is more complex components!

    Since Sling Models are Java POJO’s, and not OSGi Services, the usual OSGi injection annotations @Reference cannot be used, instead Sling Models provide a special @OSGiService annotation that provides similar functionality.

  4. Update BylineImpl.java to include the OSGiService annotation to inject the ModelFactory:

    import org.apache.sling.models.factory.ModelFactory;
    import org.apache.sling.models.annotations.injectorspecific.OSGiService;
    ...
    public class BylineImpl implements Byline {
        ...
        @OSGiService
        private ModelFactory modelFactory;
    }
    

    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. To obtain these, more Sling Model annotations are used!

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

  5. Add the @Self annotation to get the SlingHttpServletRequest request:

    import org.apache.sling.models.annotations.injectorspecific.Self;
    ...
    @Self
    private SlingHttpServletRequest request;
    

    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).

  6. Add @PostConstruct method:

    import javax.annotation.PostConstruct;
    ...
    public class BylineImpl implements Byline {
        ...
        private Image image;
    
        @PostConstruct
        private void init() {
            image = modelFactory.getModelFromWrappedRequest(request,
                                                            request.getResource(),
                                                            Image.class);
        }
        ...
    }
    

    Remember, Sling Models are NOT OSGi Services, so it is safe to maintain class state. Often @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).

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

    /**
        * @return the Image Sling Model of this resource, or null if the resource cannot create a valid Image Sling Model.
    */
    private Image getImage() {
        return image;
    }
    
  8. Let’s head back to isEmpty() and finish the implementation:

    @Override
    public boolean isEmpty() {
        ...
        } else if (getImage() == null || StringUtils.isBlank(getImage().getSrc())) {
            // A valid image is required
            return true;
        } else {
        ...
    }
    

    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 overly costly, but worth avoiding calling unnecessarily.

  9. The final BylineImpl.java should look like:

    
    package com.adobe.aem.guides.wknd.core.models.impl;
    
    import java.util.ArrayList;
    import java.util.Collections;
    import java.util.List;
    
    import javax.annotation.PostConstruct;
    
    import org.apache.commons.lang3.StringUtils;
    import org.apache.sling.api.SlingHttpServletRequest;
    import org.apache.sling.models.annotations.DefaultInjectionStrategy;
    import org.apache.sling.models.annotations.Model;
    import org.apache.sling.models.annotations.injectorspecific.OSGiService;
    import org.apache.sling.models.annotations.injectorspecific.Self;
    import org.apache.sling.models.annotations.injectorspecific.ValueMapValue;
    import org.apache.sling.models.factory.ModelFactory;
    
    import com.adobe.aem.guides.wknd.core.models.Byline;
    import com.adobe.cq.wcm.core.components.models.Image;
    
    @Model(
            adaptables = {SlingHttpServletRequest.class},
            adapters = {Byline.class},
            resourceType = {BylineImpl.RESOURCE_TYPE},
            defaultInjectionStrategy = DefaultInjectionStrategy.OPTIONAL
    )
    public class BylineImpl implements Byline {
        protected static final String RESOURCE_TYPE = "wknd/components/content/byline";
    
        @Self
        private SlingHttpServletRequest request;
    
        @OSGiService
        private ModelFactory modelFactory;
    
        @ValueMapValue
        private String name;
    
        @ValueMapValue
        private List<String> occupations;
    
        private Image image;
    
        @PostConstruct
        private void init() {
            image = modelFactory.getModelFromWrappedRequest(request, request.getResource(), Image.class);
        }
    
        @Override
        public String getName() {
            return name;
        }
    
        @Override
        public List<String> getOccupations() {
            if (occupations != null) {
                Collections.sort(occupations);
                return new ArrayList<String>(occupations);
            } else {
                return Collections.emptyList();
            }
        }
    
        @Override
        public boolean isEmpty() {
            final Image image = getImage();
    
            if (StringUtils.isBlank(name)) {
                // Name is missing, but required
                return true;
            } else if (occupations == null || occupations.isEmpty()) {
                // At least one occupation is required
                return true;
            } else if (image == null || StringUtils.isBlank(image.getSrc())) {
                // A valid image is required
                return true;
            } else {
                // Everything is populated, so this component is not considered empty
                return false;
            }
        }
    
        /**
        * @return the Image Sling Model of this resource, or null if the resource cannot create a valid Image Sling Model.
        */
        private Image getImage() {
            return image;
        }
    }
    
    

Byline HTL

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

<div data-sly-use.placeholderTemplate="core/wcm/components/commons/v1/templates.html">
</div>
<sly data-sly-call="${placeholderTemplate.placeholder @ isEmpty=false}"></sly>

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

  • 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 box with the component title, as defined above in the cq:Component’s jcr:title property.

  • 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 HTL

  1. Update byline.html with the following skeletal HTML structure:

    <div data-sly-use.placeholderTemplate="core/wcm/components/commons/v1/templates.html"
        class="cmp-byline">
            <div class="cmp-byline__image">
                <!-- Include the Core Components Image Component -->
            </div>
            <h2 class="cmp-byline__name"><!-- Include the name --></h2>
            <p class="cmp-byline__occupations"><!-- Include the occupations --></p>
    </div>
    <sly data-sly-call="${placeholderTemplate.placeholder @ isEmpty=true}"></sly>
    

    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.

Instantiating Sling Model objects in HTL

The Use block statement is 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.models.Byline" uses the Byline interface (com.adobe.aem.guides.wknd.models.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>).

  1. Update the outer div to reference the Byline Sling Model by its public interface:

    <div data-sly-use.byline="com.adobe.aem.guides.wknd.core.models.Byline"
        data-sly-use.placeholderTemplate="core/wcm/components/commons/v1/templates.html"
        class="cmp-byline">
        ...
    </div>
    

Accessing Sling Model methods

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.

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

    Update the h2 tag:

    <h2 class="cmp-byline__name">${byline.name}</h2>
    

Using HTL Expression Options

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.

  1. To join the list of occupations with ", ", the following code is used:

    <p class="cmp-byline__occupations">${byline.occupations @ join=', '}</p>
    

Conditionally displaying the placeholder

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:

  1. Update the outer div to save an HTL variable named hasContent:

     <div data-sly-use.byline="com.adobe.aem.guides.wknd.core.models.Byline"
          data-sly-use.placeholderTemplate="core/wcm/components/commons/v1/templates.html"
          data-sly-test.hasContent="${!byline.empty}"
          class="cmp-byline">
          ...
    </div>
    

    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.

  2. Update the conditional call to the placeholderTemplate at the bottom of the file with the following:

    <sly data-sly-call="${placeholderTemplate.placeholder @ isEmpty=!hasContent}"></sly>
    

Display the Image using Core Components

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

<!--/* current progress of byline.html */-->
<div data-sly-use.byline="com.adobe.aem.guides.wknd.core.models.Byline"
     data-sly-use.placeholderTemplate="core/wcm/components/commons/v1/templates.html"
     data-sly-test.hasContent="${!byline.empty}"
     class="cmp-byline">
    <div class="cmp-byline__image">
        <!-- Include the Core Components Image component -->
    </div>
    <h2 class="cmp-byline__name">${byline.name}</h2>
    <p class="cmp-byline__occupations">${byline.occupations @ join=', '}</p>
</div>
<sly data-sly-call="${placeholderTemplate.placeholder @ isEmpty=!hasContent}"></sly>

Since we use sling:resourceSuperType 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 is a powerful pattern for component re-use. For this, HTL’s data-sly-resource block is used.

  1. Replace the div with a class of cmp-byline__image with the following:

    <div class="cmp-byline__image"
        data-sly-resource="${ '.' @ resourceType = 'core/wcm/components/image/v2/image' }"></div>
    

    This data-sly-resource, included the current resource via the relative path '.', and forces the inclusion of the current resource (or the byline content resource) with the resource type 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.

  2. Completed byline.html below:

    <div data-sly-use.byline="com.adobe.aem.guides.wknd.core.models.Byline"
        data-sly-use.placeholderTemplate="core/wcm/components/commons/v1/templates.html"
        data-sly-test.hasContent="${!byline.empty}"
        class="cmp-byline">
        <div class="cmp-byline__image"
             data-sly-resource="${ '.' @ resourceType = 'core/wcm/components/image/v2/image' }">
        </div>
            <h2 class="cmp-byline__name">${byline.name}</h2>
            <p class="cmp-byline__occupations">${byline.occupations @ join=','}</p>
    </div>
    <sly data-sly-call="${placeholderTemplate.placeholder @ isEmpty=!hasContent}"></sly>
    
  3. Deploy the code base to a local AEM instance. Since major changes were made to the POM files, perform a full Maven build from the project’s root directory.

    WARNING

    Note that the WKND project is setup such that ui.content will overwrite any changes in the JCR, therefore we want to ensure we only deploy the ui.apps project to avoid wiping out the Byline component added to the article page earlier.

    $ cd ~/code/aem-guides-wknd/ui.apps
    $ mvn -PautoInstallPackage clean install
    ...
    Package imported.
    Package installed in 338ms.
    [INFO] ------------------------------------------------------------------------
    [INFO] BUILD SUCCESS
    [INFO] ------------------------------------------------------------------------
    

Reviewing the un-styled Byline component

  1. After deploying the update, navigate to the Ultimate Guide to LA Skateparks page, or wherever you added the Byline component earlier in the chapter.

  2. The image, name, and occupations now appears and we have a un-styled, but working Byline component.

    un-styled byline component

Reviewing the Sling Model registration

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 is not displayed in this list, then there was is likely an issue with the Sling Model’s annotations or the Sling Model was not added to the registered Sling Models package (com.adobe.aem.guides.wknd.core.models) in the core project.

Byline Sling Model registered

http://localhost:4502/system/console/status-slingmodels

Byline styles

The Byline component needs to be styled to align with the creative design for the Byline component. This will be achieved by using SCSS, which AEM provides support for via the ui.frontend Maven sub-project.

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

byline mock styles

Byline component design as defined by the WKND creative team

Add a default style

Add default styles for the Byline component. In the ui.frontend project under /src/main/webpack/components/content:

  1. Create a new folder named byline.

  2. Create a new folder beneath the byline folder named scss.

  3. Create a new file beneath byline/scss folder named byline.scss.

  4. Create a new folder beneath the byline/scss folder named styles.

  5. Create a new file beneath byline/scss/styles folder named default.scss.

    byline project explorer

  6. Start by populating byline.scss to include the default style:

     /* WKND Byline styles */
    @import 'styles/default';
    
  7. Add the Byline implementations CSS (written as SCSS) into the default.scss:

    .cmp-byline {
        $imageSize: 60px;
    
        .cmp-byline__image {
            float: left;
    
        /* This class targets a Core Component Image CSS class */
        .cmp-image__image {
            width: $imageSize;
            height: $imageSize;
            border-radius: $imageSize / 2;
            object-fit: cover;
            }
        }
    
        .cmp-byline__name {
            font-size: $font-size-large;
            font-family: $font-family-serif;
            padding-top: 0.5rem;
            margin-left: $imageSize + 25px;
            margin-bottom: .25rem;
            margin-top:0rem;
        }
    
        .cmp-byline__occupations {
            margin-left: $imageSize + 25px;
            color: $gray;
            font-size: $font-size-xsmall;
            text-transform: uppercase;
        }
    }
    
  8. Open the file main.scss in the ui.frontend project under /src/main/webpack/site and add the following line in the /* Components */ section:

    @import '../components/content/byline/scss/byline.scss';
    
  9. Build and compile the ui.frontend module using NPM:

     $ cd ~/code/aem-guides-wknd/ui.frontend
     $ npm run dev
    
  10. Build and deploy the ui.apps project, which will transitively include the ui.frontend project, to a local AEM instance using Maven:

     $ cd ~/code/aem-guides-wknd/ui.apps
     $ mvn clean install -PautoInstallPackage
    
    TIP

    You may need to 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.

Putting It Together

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

finished byline component

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

Congratulations!

Congratulations, you have just created a custom component from scratch using Adobe Experience Manager!

Next steps

Continue to learn about AEM Component development by exploring how to write JUnit tests for the Byline Java code to ensure everything is developed properly, and implemented business logic is correct and complete.

View the finished code on GitHub or review and deploy the code locally at on the Git brach custom-component/solution.

  1. Clone the github.com/adobe/aem-guides-wknd repository.
  2. Check out the custom-component/solution branch

Troubleshooting

Missing source folders

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.

Unresolved packages

troubleshoot unresolved packages

NOTE

If you have unresolved package imports for some of the new dependencies added to the core project, try updating the aem-guides-wknd maven project, which will in turn update all sub-projects. You can do this by right-clicking aem-guides-wknd > Maven > Update Project.

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