Java to scala

(partly) How we moved from ^ Java to Scala Graham Tackley guardian.co.uk Thursday, 7 October 2010

History • Java shop since 2006 • guardian.co.uk: java + spring + velocity + hibernate + oracle • ~100k lines production java code (and ~35k xml...) Thursday, 7 October 2010

Content API • Provide API 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 Thursday, 7 October 2010

December 2009 • Started new Content API implementation • java + guice + guice servlets + apache solr Thursday, 7 October 2010

December 2009 • A few people had played with scala • No production scala code Thursday, 7 October 2010

January 2010 • Comprehensive integration 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 Thursday, 7 October 2010

January 2010 Thursday, 7 October 2010

January 2010 • A fair bit of our test code was java- without-semicolons as we learnt about Scala... Thursday, 7 October 2010

January 2010 Thursday, 7 October 2010

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 Thursday, 7 October 2010

February 2010 Still some very java-like code... Thursday, 7 October 2010

February 2010 ... immediate win with non-IDE generated constructors ... Thursday, 7 October 2010

February 2010 ... and some things much more readable than Java Thursday, 7 October 2010

July 2010 • Switched from maven to simple-build-tool • Mainly for incremental compilation • ~ test-quick and ~ prepare-webapp also invaluable Thursday, 7 October 2010

Feb-Oct 2010 • Much learning within the team as to how to write concise, readable Scala code Thursday, 7 October 2010

Option or How we learned 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) => ... } Thursday, 7 October 2010

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 Thursday, 7 October 2010

map & ﬂatMap it took us a while to realise that most of the loops we wrote in Java were actually “map” or “ﬂatMap” Thursday, 7 October 2010

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 Thursday, 7 October 2010

Thursday, 7 October 2010

Summary • Migration path from 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 Thursday, 7 October 2010

• 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 Thursday, 7 October 2010

Java to scala

by Skills Matter on Oct 07, 2010

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