Custom Component

This tutorial covers the end-to-end creation of a custom Byline AEM 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 successfully completed the previous chapter, you can reuse the project and skip the steps for checking out the starter project.

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

  1. Check out the tutorial/custom-component-start branch from GitHub

    $ cd aem-guides-wknd
    $ git checkout tutorial/custom-component-start
    
  2. Deploy code base to a local AEM instance using your Maven skills:

    $ mvn clean install -PautoInstallSinglePackage
    
    NOTE

    If using AEM 6.5 or 6.4, append the classic profile to any Maven commands.

    $ mvn clean install -PautoInstallSinglePackage -Pclassic
    

You can always view the finished code on GitHub or check out the code locally by switching to the branch tutorial/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 are going build

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

byline component example

Byline component

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

  • Name
  • Image
  • Occupations

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 is used to handle the authoring and rendering of the Byline’s image, so it must be set as this component’s sling:resourceSuperType.

Create Component Definition

  1. In the ui.apps module, navigate to /apps/wknd/components and create a folder named byline.

  2. Inside the byline folder, add a file named .content.xml

    dialog to create node

  3. Populate the .content.xml file with the following:

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

    The above XML file provides the definition for the component, including the title, description, and group. The sling:resourceSuperType points to core/wcm/components/image/v2/image, which is the Core Image Component.

Create the HTL script

  1. Inside the byline folder, add a file byline.html, which is responsible for the HTML presentation of the component. Naming the file the same as the folder is important, as it becomes the default script Sling uses 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>
    

The 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 its 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. Inside the byline folder, create a folder named _cq_dialog.

  2. Inside the byline/_cq_dialog, add a file named .content.xml. This is the XML definition for the dialog. Add the following XML:

    <?xml version="1.0" encoding="UTF-8"?>
    <jcr:root xmlns:sling="http://sling.apache.org/jcr/sling/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"
                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 dialog node definitions use the 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. Inside the byline folder, create a folder named _cq_design_dialog.

  2. Inside the byline/_cq_design_dialog, create a file named .content.xml. Update the file with the following: 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. Synchronize the changes in ui.apps with your IDE or using your Maven skills.

    Export to AEM server byline component

Add the component to a page

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

Add an image to the AEM Assets

First, upload a sample head shot to AEM Assets to use to populate the image in the Byline component.

  1. Navigate to the LA Skateparks folder in AEM Assets: http://localhost:4502/assets.html/content/dam/wknd/en/magazine/la-skateparks.

  2. Upload the head shot for stacey-roswells.jpg to the folder.

    Headshot uploaded to AEM Assets

Author the component

Next, add the Byline component to a page in AEM. Because the Byline component is added to the WKND Sites Project - Content Component Group, via the ui.apps/src/main/content/jcr_root/apps/wknd/components/byline/.content.xml definition, it is automatically available to any Container whose Policy allows the WKND Sites Project - Content component group. Thus it’s available in the Article Page’s Layout Container .

  1. Navigate to the LA Skatepark article at: http://localhost:4502/editor.html/content/wknd/us/en/magazine/guide-la-skateparks.html

  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

  3. Ensure that the left sidebar is openand visible, and theAsset Finder** is selected.

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

  5. 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.

    add image to dialog

  6. 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 that is implemented in the Sling Model is verified.

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

    populate properties of byline 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. Therefore only the placeholder shows up.

  7. 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 LA Skate Parks page, i.e /content/wknd/us/en/magazine/guide-la-skateparks/jcr:content/root/container/container/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

Create Byline Sling Model

Next, let’s 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™ POJOs (Plain Old Java™ Objects) that facilitate the mapping of data from the JCR to Java™ variables, and provide efficiency when developing in the AEM context.

Review Maven Dependencies

The Byline Sling Model relies on several Java™ APIs provided by AEM. These APIs are made available via the dependencies listed in the core module’s POM file. The project used for this tutorial has been built for AEM as a Cloud Service. However it is unique as it’s backward compatible with AEM 6.5/6.4. Therefore both dependencies for Cloud Service and AEM 6.x are included.

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

  2. Find the dependency for aem-sdk-api - AEM as a Cloud Service Only

    <dependency>
        <groupId>com.adobe.aem</groupId>
        <artifactId>aem-sdk-api</artifactId>
    </dependency>
    

    The aem-sdk-api contains all public Java™ APIs exposed by AEM. The aem-sdk-api is used by default when building this project. The version is maintained in the Parent reactor pom from the root of the project at aem-guides-wknd/pom.xml.

  3. Find the dependency for the uber-jar - AEM 6.5/6.4 Only

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

    The uber-jar is only included when the classic profile is invoked, i.e mvn clean install -PautoInstallSinglePackage -Pclassic. Again, this is unique to this project. In a real-world project, generated from the AEM Project Archetype the uber-jar is the default if the version of AEM specified is 6.5 or 6.4.

    The uber-jar contains all public Java™ APIs exposed by AEM 6.x. The version is maintained in the Parent reactor pom from the root of the project aem-guides-wknd/pom.xml.

  4. 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 complete 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 or aem-sdk-api.

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

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

Byline interface

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

  1. Inside, the core module within the core/src/main/java/com/adobe/aem/guides/wknd/core/models folder create a file named Byline.java

    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; this is reviewed later.

  3. Java™ packages that contain public Java™ classes, in this case a Sling Model, must be versioned using the package’s package-info.java file.

    Since the WKND source’s Java™ package com.adobe.aem.guides.wknd.core.models declares version of 1.0.0, and a non-breaking public interface and methods are being added, the version must be increased to 1.1.0. Open the file at core/src/main/java/com/adobe/aem/guides/wknd/core/models/package-info.java and update @Version("1.0.0") to @Version("2.1.0").

    ```
    @Version("2.1.0")
    package com.adobe.aem.guides.wknd.core.models;
    
    import org.osgi.annotation.versioning.Version;
    ```
    

Whenever a changes are made to the files in this package, the package version must be adjusted semantically. If not, the Maven project’s bnd-baseline-maven-plugin detects an invalid package version and break the built. Luckily, on failure, the Maven plugin reports the invalid Java™ package version and the version it should be. Update the @Version("...") declaration in the violating Java™ package’s package-info.java to the version recommended by the plugin to fix.

Byline implementation

The 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. Create a folder named impl beneath core/src/main/java/com/adobe/aem/guides/core/models.

  2. In the impl folder, create a file BylineImpl.java.

    Byline Impl File

  3. Open BylineImpl.java. Specify that it implements the Byline interface. Use the auto-complete features of the IDE or manually update the file to include the methods needed to implement the Byline interface:

    package com.adobe.aem.guides.wknd.core.models.impl;
    import java.util.List;
    import com.adobe.aem.guides.wknd.core.models.Byline;
    
    public class BylineImpl implements Byline {
    
        @Override
        public String getName() {
            // TODO Auto-generated method stub
            return null;
        }
    
        @Override
        public List<String> getOccupations() {
            // TODO Auto-generated method stub
            return null;
        }
    
        @Override
        public boolean isEmpty() {
            // TODO Auto-generated method stub
            return false;
        }
    }
    
  4. 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/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 implementation 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 that is implemented is getName(), it 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 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 loads 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;
    ...
    @Override
    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, the business requirement is 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 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:

Check if the fileReference JCR property resolves to an asset. OR Convert this resource into a Core Component Image Sling Model and ensure the getSrc() method is not empty.

Let’s use the second approach. The first approach is likely sufficient, but in this tutorial the latter is used to allow us to explore other features of Sling Models.

  1. Create a private method that gets the Image. This method is left private because there is no need to expose the Image object in the HTL itself, and it’s only used to drive isEmpty().

    Add 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

    The second uses the Apache Sling ModelFactory OSGi service, which is a handy service, and helps us create Sling Models of other types in Java™ code.

    Let’s use 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 the second approach is used, as it requires to explore more facets of Sling Models that are 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.

  2. 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.

  3. 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 this 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 more exploratory modelFactory approach.

    Now the variables necessary to instantiate the Image model via the ModelFactory API are injected. Let’s 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).

  4. 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.

    If the @PostConstruct method throws an exception, the Sling Model is not instantiated and it is null.

  5. 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;
    }
    
  6. Let’s head back to isEmpty() and finish the implementation:

    @Override
    public boolean isEmpty() {
       final Image componentImage = 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 (componentImage == null || StringUtils.isBlank(componentImage.getSrc())) {
            // A valid image is required
            return true;
        } else {
            // Everything is populated, so this component is not considered empty
            return false;
        }
    }
    

    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.

  7. 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/byline";
    
        @Self
        private SlingHttpServletRequest request;
    
        @OSGiService
        private ModelFactory modelFactory;
    
        @ValueMapValue
        private String name;
    
        @ValueMapValue
        private List<String> occupations;
    
        private Image image;
    
        /**
        * @PostConstruct is immediately called after the class has been initialized
        * but BEFORE any of the other public methods.
        * It is a good method to initialize variables that is used by methods in the rest of the model
        *
        */
        @PostConstruct
        private void init() {
            // set the image object
            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 componentImage = 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 (componentImage == null || StringUtils.isBlank(componentImage.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/byline/byline.html that was created in the earlier setup 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.

The 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 an 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 are 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 use the placeholder paradigm to provide a visual cue to authors indicating a component is incorrectly authored and it is not displayed on AEM Publish. The convention to drive this decision is to implement a method on the component’s backing Sling Model, in this case: Byline.isEmpty().

The isEmpty() method is invoked on the Byline Sling Model and the result (or rather it’s 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 key, it both sets an HTL variable and renders/doesn’t render the HTML element it’s on. It is based on the result of the HTL expression evaluation. If “true”, the HTML element renders, else it does not render.

    This HTL variable hasContent can now be reused 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.

As the sling:resourceSuperType points to the Core Component’s Image component to author the image, the Core Component’s Image component can be used to render the image.

For this, let’s include the current byline resource, but force the resource type of the Core Component’s Image component, using resource type core/wcm/components/image/v2/image. This is a powerful pattern for component reuse. 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, includes 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 the content.

  2. Completed byline.html below:

    <!--/* 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="${!byline.empty}"
        class="cmp-byline">
        <div class="cmp-byline__image"
            data-sly-resource="${ '.' @ 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 changes were made to core and ui.apps both modules need to be deployed.

    $ cd aem-guides-wknd/ui.apps
    $ mvn clean install -PautoInstallPackage
    
    $ cd ../core
    $ mvn clean install -PautoInstallBundle
    

    To deploy to AEM 6.5/6.4 invoke the classic profile:

    $ cd ../core
    $ mvn clean install -PautoInstallBundle -Pclassic
    
    CAUTION

    You could also build the entire project from the root using the Maven profile autoInstallSinglePackage but this may overwrite the content changes on the page. This is because the ui.content/src/main/content/META-INF/vault/filter.xml has been modified for the tutorial starter code to cleanly overwrite the existing AEM content. In a real-world scenario, this is not an issue.

Reviewing the unstyled 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 appear and an unstyled, but working Byline component is present.

    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, it is likely an issue with the Sling Model’s annotations or the Model was not added to the correct 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

To align the Byline component with the provided creative design, let’s style it. This is achieved by using SCSS file and updating the file in the ui.frontend module.

Add a default style

Add default styles for the Byline component.

  1. Return to the IDE and the ui.frontend project under /src/main/webpack/components:

  2. Create a file named _byline.scss.

    byline project explorer

  3. Add the Byline implementations CSS (written as SCSS) into the _byline.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-medium;
            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;
        }
    }
    
  4. Open a terminal and navigate into the ui.frontend module.

  5. Start the watch process with the following npm command:

    $ cd ui.frontend/
    $ npm run watch
    
  6. Return to the browser and navigate to the LA SkateParks article. You should see the updated styles to the component.

    finished byline component

    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.

Congratulations!

Congratulations, you have 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 branch tutorial/custom-component-solution.

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

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