How to create an AEM Custom global object?

Overview
As an AEM developer, you know that there are a set of global objects available in AEM at the view layer. Whether you can use JSP or New template framework (HTL). Most commons global objects are currentPage, current resource, current design object etc.

These set of objects are initialized by the AEM application by default & available to use them in every component.

Do you really need custom object?
With given architecture of AEM & Sling framework to resolve the resource, there is a situation when you need your own custom object to be available across the application components. Just like global objects.

Let’s consider a multi-brand site where you need some brand-specific information, Objects or JSON etc should be available at each brand application level. It means object should be available at every component.

General Solution
General practice is that have a common bean/Use class gets initialized at each component level. Performance wise, initializing a bean at every component level, isn’t that bad. Because most of the content gets cached. However, It is an issue when you have got that information/object through service. You can’t make a web service from every component. You could still do that if you are an architect & developer has an alternative solution. So let’s see an alternative solution.

Alternative Solution
An alternative solution is pretty simple. Just like any other AEM global objects, keep your custom object available at every component by default. No initialization of any objects. Make sense? let’s see the following steps to create global custom objects.

1. Create a new class with an appropriate name (hard to find the appropriate name but try it).
2. Make sure new class is registered as Component in OSGI Console.
3. Sling Framework provides an interface BindingValuesProvider. Implement this interface. This interface provides addBindings(Bindings bindings) method.
4. Bindings parameter works like a map. You need to put key & value in it. For instance, bindings.put(“myObject”, “valueOfCustomObject”);
5. Now, “myObject” can be used as a global variable anywhere in the components.

Sample src Code

# CustomGlobalObject

import org.apache.felix.scr.annotations.Component;

import org.apache.felix.scr.annotations.Reference;

import org.apache.felix.scr.annotations.Service;

import org.apache.sling.scripting.api.BindingsValuesProvider;

import javax.script.Bindings;

@Component

@Service

public class CustomGlobalObject implements BindingsValuesProvider {

    @Reference

    IMyService iMyService;

    @Override

    public void addBindings(Bindings bindings) {

        bindings.put("mylist", iMyService.getGlobalObject());

    }

}

#Service Interface

import java.util.List;

public interface IMyService {

    List getGlobalObject();

}

#Service Interface implementation

import org.apache.felix.scr.annotations.Component;

import org.apache.felix.scr.annotations.Service;

import java.util.ArrayList;

import java.util.List;

@Component

@Service

public class MyService implements IMyService{

    @Override

    public List<String> getGlobalObject() {

        List list = new ArrayList();

        list.add("a"); list.add("b"); list.add("c");

        return list;

    }

}

# Entry in Sightly HTML component

Custom object: ${mylist}

#Output

Custom object: a,b,c

Final Thought:
There could be other good solutions to solve the problem which I described in this post. Would love to hear others ideas. Don’t hesitate to share your thoughts in the comment section. For any doubt or question, leave a comment. will do our best to answer your questions. Thanks in advance.

References
https://sling.apache.org/documentation/bundles/scripting/scripting-htl.html
https://sling.apache.org/documentation/bundles/models.html