We won't be able to progress much further without the ability to save our objects, namely cats, into some kind of persistent storage. 

For that, we'll need to connect to the database first.

Add the following two lines to your build.gradle dependencies section:

compile group: 'org.postgresql', name: 'postgresql', version: '42.2.2'
compile group: 'io.vertx', name: 'vertx-jdbc-client', version: $vertx_version

The first line of code fetches the PostgreSQL driver. The second one adds the Vert.x JDBC client, which allows Vert.x, having the driver, to connect to any database that supports JDBC.