We use Apache Maven because it is a standard. Gradle is very good alternative, but Gradle doesn't provide any advantage for our project. Gradle is slower (without running daemon), need more resources and a learning curve is quite big. Our project can not use a great flexibility of Gradle. On the other hand, Maven is well-know tool integrated in many IDEs, Dockers and so on.
Some may wonder why did we choose Grails ? Really good question :) We spent quite some time to evaluate what framework to go with and the battle was between Play Scala and Grails ( Groovy ). We have enough experience with both and, to be honest, I absolutely in love with Scala; however, the tipping point for us was the potential speed of development. Grails allows much faster development pace than Play , and as of right now this is the most important parameter. We might convert later though. Also, worth mentioning, by default Grails comes with Gradle as a build tool, so why change?
At the heart of Uber’s mobile app development are four primary apps: Android rider, Android driver, iOS rider, and iOS driver. Android developers build in Java, iOS in Objective C and Swift. Engineers across both platforms land code into a monolithic code base that ships each week.
They use some third-party libraries, but often build their own, since “Many open source libraries available are general-purpose, which can create binary bloat. For mobile engineering, every kilobyte matters.”
On Android, the build system is Gradle. For the UI, Butter Knife binds views and callbacks to fields and methods via annotation processing, and Picasso provides image loading.
As for iOS, all of the code lives in a monorepo built with Buck. For crash detection, KSCrash reports crashes to the internal reporting framework.
All Java-Projects are compiled using Apache Maven. We prefer it over Apache Ant and Gradle as it combines lightweightness with feature-richness and offers basically all we can imagine from a software project-management tool and more. We're open however to re-evaluate this decision in favor of Gradle or Bazel in the future if we feel like we're missing out on anything.