Java to scala

(partly) How we moved from ^ Java to Scala Graham Tackley guardian.co.uk

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

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

December 2009 • Started new Content API implementation • java + guice + guice servlets + apache solr

December 2009 • A few people had played with scala • No production scala code

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

January 2010

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

January 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

February 2010 Still some very java-like code...

February 2010 ... immediate win with non-IDE generated constructors ...

February 2010 ... and some things much more readable than Java

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

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

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) => ... }

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

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

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

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

• 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

Java to scala

by Graham Tackley

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Java to scala

by Graham Tackley

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Java to scala Presentation Transcript

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