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Java to scala
The document discusses The Guardian's migration from a Java-based architecture to one using Scala for their Content API project. They started by writing integration tests in Scala with ScalaTest in January 2010 and enjoyed it so much that after a month, in February 2010, they decided to convert the whole application to Scala. It took some time for the team to learn how to write good Scala code, like embracing the Option type to avoid nulls and using map and flatMap instead of loops. The migration was relatively smooth by embracing Scala features incrementally. [END SUMMARY]
Java to scala
- 1. (partly) How we movedfrom ^ Java to Scala Graham Tackley guardian.co.uk
- 2. History • Java shopsince 2006 • guardian.co.uk: java + spring + velocity + hibernate + oracle • ~100k lines production java code (and ~35k xml...)
- 3. Content API • ProvideAPI to access all of our website content • Limited beta released early 2009 • Started implementation of final version late 2009 • Live April 2010: http://content.guardianapis.com
- 4. December 2009 • Startednew Content API implementation • java + guice + guice servlets + apache solr
- 5. December 2009 • Afew people had played with scala • No production scala code
- 6. January 2010 • Comprehensiveintegration tests were very important to us • Started writing our integration tests in Scala with the awesome ScalaTest • Already a maven project, so mixed scala- java support easy with maven-scala-plugin
- 7.
- 8. January 2010 • Afair bit of our test code was java- without-semicolons as we learnt about Scala...
- 9.
- 10. February 2010 • ...despite that we loved it so much that after a month we decided to convert the whole app to Scala • scala + guice + guice servlets + apache solr
- 11. February 2010 Still somevery java-like code...
- 12. February 2010 ... immediatewin with non-IDE generated constructors ...
- 13. February 2010 ... andsome things much more readable than Java
- 14. July 2010 • Switchedfrom maven to simple-build-tool • Mainly for incremental compilation • ~ test-quick and ~ prepare-webapp also invaluable
- 15. Feb-Oct 2010 • Muchlearning within the team as to how to write concise, readable Scala code
- 16. Option or How welearned to stop worrying and love the Option We’d read “don’t use nulls, use Option instead” DAY ONE s/x == null/x.isDefined DAY THREE x match { case None => ... case Some(value) => ... }
- 17. Option or How we learned to stop worrying and love the Option WEEK THREE TODAY We now think of Options as lists with zero or one entries
- 18. map & flatMap ittook us a while to realise that most of the loops we wrote in Java were actually “map” or “flatMap”
- 19. Java Libraries Content API extensively uses Solr/J, which is good but returns loads of nulls And don’t get me started on HttpServletRequest... We used implicit conversions to hide the Java yuk
- 21. Summary • Migration pathfrom Java relatively smooth • Take it easy, and don’t fear java-without- semicolons in the early days • An incremental embrace of Scala features worked really well for us • Hide the Java yuk with implicit conversions
- 22. • http://content.guardianapis.com • http://www.guardian.co.uk/open-platform •http://github.com/guardian/open-platform- content-api-scala-client • http://blog.tackley.net graham.tackley@guardian.co.uk