This document summarizes Tim Soethout's presentation on introducing Scala into an existing Java project at ING Bank. The presentation covered compiling Scala in Maven, mixing Java and Scala source code, measuring code coverage for both languages, performing code quality analysis with SonarQube, and generating documentation for Java consumers from Scala code. The goal was to integrate Scala development within the enterprise compliance and tooling requirements for a large existing Java codebase.

1. Introducing Scala in your
existing Java project
Tim Soethout - ING Bank
http://blog.timmybankers.nl

2. Overview
Intro
Scala @ ING - Context
Compiling Scala in Maven
Mixing Java and Scala source
Code coverage
Code quality using Sonar
More code analysis
Documentation for Java consumers
Wrap up

3. Who am I?
Tim Soethout
Functional programmer at heart
Scala evangelist/trainer inside ING
More recently: Aquarium enthusiast & West Coast Swing-
dancer

4. Scala @ ING

5. State
Much Java with Maven
Some Scala for restful services using Akka
Open source: Coral
Developers are getting interested and looking for
possibilities

6. Context
Maven project written in Java 6
Team with mixed Scala experience levels
Eager to do Scala
But within Enterprise: Compliancy

7. Compiling Scala in Maven

8. scala-maven-plugin
<project>
<build>
<sourceDirectory>src/main/scala</sourceDirectory>
<testSourceDirectory>src/test/scala</testSourceDirectory>
<plugins>
<plugin>
<groupId>net.alchim31.maven</groupId>
<artifactId>scala-maven-plugin</artifactId>
<version>3.2.2</version>
...
</plugin>
</plugins>
</build>
</project>

9. Mixing Java and Scala
source

10. Demo
Mixed Java & Scala

11. Demo
Multiple modules

12. Mixing it up
Seems to work on first sight
Problems can arise in:
Multiple modules
Dependencies from Java to Scala
Depends on compile order
sbt incremental compiler to the rescue
scala-maven-plugin:
<configuration>
<recompileMode>incremental</recompileMode>
</configuration>

13. Another option; runs sbt underneath
Not really maintained anymore, but helped us a lot 6
months ago
sbt-compiler-maven-plugin
<plugin>
<groupId>com.google.code.sbt-compiler-maven-plugin</groupId>
<artifactId>sbt-compiler-maven-plugin</artifactId>
<version>1.0.0-beta5</version>
<executions>
<execution>
<goals>
<goal>compile</goal>
<goal>testCompile</goal>
<goal>addScalaSources</goal>
</goals>
<id>default-sbt-compile</id>
</execution>
</executions>
</plugin>

14. Code coverage

15. Cobertura, Jacoco, Clover, EclEmma?!?
Works good for Java
Line and branch coverage

16. Demo
Let's try it for Scala!

17. That's awful!
Scala compiler generates lots for you (i.e. in case classes,
traits etc)
Cobertura and Jacoco work on byte code
ergo lots of uncovered generated code
I don't want to be testing generated code, would you?

18. to the rescue!
Scala statement and branch coverage!
scoverage-maven-plugin

19. Demo
Let's try it for Scala!

20. So what did we do?!
Statement coverage for Scala with scoverage
Normal line/branch coverage for Java with Cobertura

21. Code quality using Sonar

22. Code Quality Platform
Code metrics
Coverage
Complexity
Size
Rules
Spot regression
SonarQube

23. Tooling
docker-compose script with data container, Postgres
database and SonarQube
Contains plugins needed for Scala! (Cobertura,
scoverage, Java, etc)
- updated to use cobertura only for Java
Used for filtering Scala coverage from cobertura.xml
scala-sonarqube-docker
sonar-scala-plugin
xml-transform-maven-plugin

24. Demo
Java & Scala code coverage in Sonar
*.java
cobertura
cobertura.xml
*.scala
scoverage
scoverage.xml
xml-transform-maven-plugin
Sonar Scoverage plugincobertura-without-scala.xml
Sonar Cobertura Plugin
SonarQube

25. More code analysis

26. Compiler flags Java
-Xlint:unchecked - Unchecked casts

27. Compiler flags Scala
-unchecked
-deprecation
-feature
-Xlint
-Yno-adapted-args
-Ywarn-dead-code
-Ywarn-numeric-widen
-Ywarn-value-discard
-Xfuture
-Ywarn-unused-import
-Ywarn-unused

28. Demo
Compiler flags
FindBugs & FindSecurityBugs

29. More checks - To implement
Abide
Wartremover

30. Documentation for Java
consumers

31. Generated outline of Scala files in java
including javadoc annotations
useful to generate Javadoc for Java consumers
genjavadoc

32. Demo
genjavadoc

33. Wrap up

34. Recap
Scala and Java code in
single module
multiple modules
code coverage on both
Code Quality with
SonarQube
ScalaStyle
FindBugs
Lots to tweak - compiler arguments, linters
Documentation for Java

35. Thanks for listening
Questions?
/ Slides Code

36. Important legal information
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