Break Law of Demeter Gracefully In Java

The Law of Demeter (LoD), or Principle of Least Knowledge, is a design guideline in object-oriented programming that promotes loose coupling. It states that an object should only interact with its immediate collaborators, avoiding method chains (e.g., obj.getA().getB().getC()). Following LoD improves encapsulation, maintainability, and modularity. Read more about Law of Demeter.

Let’s be honest, often times we have to break the Law of Demeter. In this article, we will discuss how to break the Law of Demeter gracefully in Java.

In AEM code, we often need to get the specific resource in sling models, services or servlets. If we have SlingHttpServletRequest object, we can get our desired resource as follows

Resource resource = request.getResourceResolver()
                           .getResource("/content/myproject/en/home");

Here we can not respect LoD because there is no other way to get the resource without getting ResourceResolver object first. Also request.ResourceResolver() method call can potentially throw a NullPointerException.

Violate LoD Gracefully

To break the Law of Demeter gracefully, we can use the Optional in Java. Optional not only lets us violate LoD but also helps us to handle NullPointerException elegantly.

Optional<Resource> resource = Optional.ofNullable(request.getResourceResolver()
                                      .getResource("/content/myproject/en/home"));

Conclusion

By using Optional not only we can break LoD gracefully but also handle NullPointerException elegantly. It is a good practice to use Optional when we are not sure about the object’s state.