Guicing up Dropwizard

Dropwizard is a lightweight RESTful web service framework built by Yammer. It incorporates a collection of mature Java libraries including Jetty, Jersey, Jackson, and Metrics to provide performant and reliable production-ready services.

At my current client, we’ve been implementing an entire micro-service backend using Dropwizard to drive content to Grails and AngularJS applications. One of the things that Dropwizard lacks is a succinct dependency injection implementation for your code. The latest released version of Dropwizard (0.6.2) uses Jersey v1.17.1 which had it’s own complicated DI framework (Jersey 2.x integrates HK2 which is a JSR-330 compliant framework).

We quickly found ourselves having to configure a substantial amount of code in our services just to wire classes together while allowing us to effectively and logically separate our business logic. So we’ve started exploring DI in Dropwizard. Guice is a lightweight DI framework. It also supports JSR-330 since v3.0.

We started integration Guice by utilizing the Dropwizard-Guice library from Hubspot. Simply add the dependency to your Dropwizard project and register the module:

This simple configuration does a couple things. First, it registers the Guice bundle with Dropwizard. This is turn will automatically register the following items with Jersey from your package:

  • HealthChecks (extends HealthCheck)
  • Tasks (extends Task)
  • Resources (has a @Path annotation)
  • Managed classes (extends Managed)
  • Injectable Providers (extends InjectableProvider)
  • Providers (extends Provider)
  • Bundles (extends Bundle)

During this process, Guice will inject any necessary dependencies into these classes (for those it has to instantiate at this point). Second, it registers a providers for both the Dropwizard Environment instance and the service’s Configuration instance. Finally, it registers a GuiceComponentProviderFactory with the Jersey IoC container.

One of the big wins with Guice is that it is capable of injecting any class that either has a no-arg constructor or has a constructor that is annotated with @Inject. This can help to quickly break up logic without having a proliferation of annotations to describe how your classes are wired up.

At this point, we had Guice wired into our services but we needed a way to inject the SessionFactory from the Dropwizard-Hibernate bundle into our DAOs. If you want to see how this was accomplished, check out my Dropwizard-Guice example project on Github.

About the Author

Object Partners profile.
Leave a Reply

Your email address will not be published. Required fields are marked *

Related Blog Posts
Interpreting Spatial Data in the Age of COVID-19
As 2020 has come to an end, many are eager to leave the mess of COVID-19 behind with the new year and gain a fresh start. Unfortunately, new cases are still soaring across the United […]
Building a Better Mousetrap
Recently, my daughter (age 6) was into building “mousetraps” out of shoe boxes. These were more or less comfortable cardboard mouse houses complete with beds, rooms, everything a mouse could want or need and not […]
ARM Wrestling Its Way Into Mainstream Software Development
Nearly all smart phones have been running ARM-based processors for years. They provide superior power for the amount of power consumed, and thus extend battery life. With Apple’s recent release of the Apple Silicon M1 […]
Video capture using WebRTC
Capturing the feed of a users camera can be a daunting undertaking involving one or multiple third party packages. Often we opt for prompting the user to upload the video or image we need, causing […]