Scala and Play with GradleWei Chen

Sr. Software Engineer, Development Tools

Gradle Summit 2015

Build Happiness

What this talk is about?

● Scala support in Gradle● Play support in Gradle● Continuous mode (watch mode)● Demos

Who am I?

● A Software Engineer at Linkedin● Development Tools● Not a Scala expert● Not a Play expert● Maybe a build expert: make, ant, maven, sbt,

and gradle

● Object oriented● Strong typed● Full support for functional programming● JVM based● 1.5% of LI code base (Java 25.1%)

(Simple Build Tool? LOL)

● De facto build tool for scala community● Native support for compiling Scala code and

integrating with many Scala test frameworks● Build descriptions written in Scala using a DSL● Dependency management using Ivy● Continuous compilation, testing, and

deployment● Integration with the Scala interpreter for rapid

iteration and debugging● Support for mixed Java/Scala projects

vs.

Sbt Gradle

DSL language Scala Groovy

Supported languages Scala, Java Java, Scala, C++, ...

Incremental Scala build Yes Possible with Zinc

Interactive Shell Yes No (but has Gradle daemon)

REPL Yes No

Multi-module support Yes Yes

Dependency Management Ivy proprietary

Continuous Mode Yes YES!

Vendor and community support Mediocre Great

Existing LI Tooling Integration Minimal when we started Great

Scala Support in Gradle

● Scala plugin● From the very beginning of Gradle● 0.8 (September 2009)● Zinc support (1.3 November 2012)

Demo

● Compiles Scala● Compiles Java● Joint compilation

Limitations

● Scala version can only be inferred from direct dependencies

● No conflicting scala version validation● No cross-build support● No native specs2 integration● Bad IDE integration● Second class citizen in Scala world● Smaller adopter community

Framework

● Web App Framework● Async I/O (JBoss Netty)● Built-in hot reloading● Built on top of sbt● Supports both Java and Scala● 159+ Play Applications

Why to build Play on Gradle

● Pains with Ivy● Simplify our processes● Unify our build technologies● DRY

Dependency Management

● Product catalog● Dependency validation● Repository management● Conflict resolution● Consistent versioning● Manifest generation/upload● Dependency resolution performance

What’s involved?

1. Assets processing and packaging

2. Routes compilation

3. Twirl templates compilation

4. Scala/Java compilation

5. Running the server in development mode

6. Play binary packaging

7. Play distribution packaging

Milestones

1. Using Gradle to build a Play application

2. Continuous Mode and Hot-Reload

3. Making it real!

Demo

● Build a play app● Start the server in development mode

Basic Sample Demo

● Apply play plugin● Declare dependencies● Configure repositories

Advanced Sample Demo

● Apply CoffeeScript plugin● Configure target Scala and Play version

Multiproject Sample Demo

● Standard Gradle multiproject build● “root” project: main Play application● 3 submodules:

○ admin: Play application○ user: Play application○ util: Java library

Continuous Mode

● Gradle does not exit● Re-execute tasks when task file inputs

change● > Java 7 (file system WatchService)

Demo

● gradle build● gradle test

Play Hot Reload

● Stateless● Lightweight● Classloader magic● Used to be tightly coupled with build system

(sbt)● BuildLink

Play Hot Reload

Demo

Hot reload● Routes● Templates● Controller class

Q & A

Thank you!Wei ChenSr. Software Engineer, Development Tools

wechen@linkedin.comhttp://www.linkedin.com/in/weichenlinkedin

Useful Links

● https://docs.gradle.org/current/userguide/scala_plugin.html● https://github.com/gradle/gradle/blob/master/design-docs/play-support.

md● https://engineering.linkedin.com/play/developing-play-applications-

using-gradle● https://github.

com/playframework/playframework/blob/master/framework/src/build-link/src/main/java/play/core/BuildLink.java

● https://github.com/gradle/gradle● https://github.com/playframework/playframework