When to use DropWizard bundles?

Question

I am curious about an elusive - but potentially very powerful - DropWizard feature called Bundles. According to the docs:

A Dropwizard bundle is a reusable group of functionality, used to define blocks of an application’s behavior.

Given that DropWizard (DW) is extremely well documented, I’m shocked that this is really the only explanation on bundles. I see a few examples of them in the wild:

• Asset Bundle
• Cassandra Bundle

But what I don’t understand is: bundles seem to just be code packaged and distributed in JARs. So why can’t I just write “raw” (non-“bundle”-compliant) Java classes to do what I need, slap them in a JAR, then include that JAR on my build/compile classpath, ad then use them in my DW app? Of what use is a DW bundle, and when should one use them?

Answer 1

Bundles are like addons to Dropwizard that make it very easy to add small pieces of functionality. For example, if you use the assets bundle, you can attach a UI to your API for testing purposes and it will run on the same port and is very easy to use. Another example would be the Migrations Bundle that easily ties Liquibase into Dropwizard so you can run database migrations with the same jar. This also works well since your API could be accessing some sql database which has connection parameters defined in a yml file, the migrations would be able to run on the same database.