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How to write plugins in a language other than Java

Stefan SaasenConfluence Team Lead, Atlassian

Polyglot Plugin Development

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• Written an Atlassian plugin in Java• Interested in other programming languages• Eager to see what is possible with Atlassian plugins

Audience

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• Who has actually written a Atlassian plugin?• In any other language than Java?

Show of hands

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Rhino

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https://bitbucket.org/ssaasen/atlassian-jruby-example-plugin

https://bitbucket.org/ssaasen/atlassian-scala-example-plugin

• Why?• How?

• Example 1: Scala

• Example 2: JRuby

• Go and do it!

Polyglot Plugins

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Why not?

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Why ?

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• Leverage existing knowledge in the team• Libraries/applications already written in language X• Time to market/devspeed• Explore technologies in a sandboxed environment• Grass looks always greener on the other side

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What to tell the boss?

• Leverage existing knowledge in the team• Libraries/applications already written in language X• Time to market/devspeed• Explore technologies in a sandboxed environment• Grass looks always greener on the other side

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What to tell the boss?

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“Succinctness”

“No time to write in Java”

“Less bugs”

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• Why?• How?

• Example 1: Scala

• Example 2: JRuby

• Go and do it!

Polyglot Plugins

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• Hybrid language: Object oriented & functional• Concise, statically typed (with type inference)• Higher order/first class functions, pattern matching• Powerful type system• Rich standard library

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How?

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Overview

Java

JVM

Java Standard Library

Scala Runtime Library

java

csc

alac

Java Bytecode*.class

Scala

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• Start with Maven to get the AMPS goodness

• Use the maven-scala-plugin

• Add SBT if necessary

Build process

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• Compile time is a concern!• FSC• Useful Maven goals:

mvn scala:ccmvn scala:console

Build process f.

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Bundle runtime

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Size might be a problem :(

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Option Scope Package Size

Bundle

Bundle & Shrink w/ProGuard

Install separately

compile mvn package -Pbundle 8.5 MB Simple

compile mvn package -Pproduction 680 KB Deploy

externally

provided mvn package 50 KB Deploy internally

Deployment options

Simply install using the plugin manager!

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• Dependencies: Scala libraries are jar files and often available from Maven repositories

• Compile time: mvn scala:cc for continuous compilation• Workflow: scala:cc & atlas-cli pi or

mvn package && atlas-install-plugin• Profit: mvn scala:console to get the Scala REPL

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Development checklist

Scala: Working with Java APIs

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• Collections• Method naming conventions• Annotations• Null vs. Option

Scala gotchas (the 80%)

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• Immutable vs Mutable, serial vs. parallel• Rich API: Prefer Scala collections• Convert between Java and Scala collections when

calling Java methods• Solution: JavaConverters (explicit, preferred) vs.

JavaConversions (implicit)• Watch out for serialization: Bandana/XStream

Collections

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• Libraries rely on bean style naming conventionse.g. XWork, Velocity

• Scala: uniform access principle• Solution: Use @BeanProperty and

@BooleanBeanProperty

Method naming conventions

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• How to use @JavaAnnotation on a getter method when defining fields?

• Scala meta annotations @beanGetter, @beanGetter, @field, @getter, @setter

(Meta)-Annotations

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• In Scala Option represents an optional value.• Don’t let the billion-dollar mistake leak into your

Scala code!• Solution: wrap nullable method calls in an Option

Option vs. null

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Show me the code!

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• Servlet & XWork action• Confluence macro• REST via Jersey/Jackson• Build setup• Use as a starting point

Example Scala plugin

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https://bitbucket.org/ssaasen/atlassian-scala-example-plugin

• Replace Java entirely with Scala or mix and match• Runtime library: 3 deployment options• Fits into the AMPS development workflow• Scala Gotchas: watch out for common problems• “Scala is a great fit to write Atlassian plugins in”

Let’s recap

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• Why?• How?

• Example 1: Scala

• Example 2: JRuby

• Go and do it!

Agenda

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• Dynamic, object-oriented language• Everything is an object (no “primitives”)• Meta-programming and open, executable classes

allow for easy creation of DSLs• JRuby: Ruby runtime written in Java

(J)Ruby

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How?

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Overview

Java

JVM

Java Standard Library

Ruby Runtime

Ruby Standard Library

RubyGems Your Ruby Code

java

cjr

ubyc

Ruby files *.rb

Java Bytecode*.class

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Plugins can’t be written in Ruby

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But we can still use Ruby in a plugin!

• Embed the Ruby Runtime• Use Java to execute Ruby scripts and classes• Make components of the host application available• Use the script execution result in Java

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Recipe for using JRuby

• javax.scripting - JSR 223• Apache Bean Scripting Framework (BSF)• JRuby Embed - lower level JRuby API

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Embedding Strategies

• javax.scripting - JSR 223 Only configurable via system properties :(

• Apache Bean scripting framework (BSF)No point in adding a separate API

• JRuby Embed - lower level JRuby API

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Embedding Strategies

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• Package Ruby files• Download and package Ruby gems• Make Ruby gems available on the Ruby LOAD_PATH• Bundle everything into a plugin jar file• A lot of Maven XML :)• Caveat: JRuby runtime is even larger!

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Building the plugin

Show me the code!

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1 minute

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• How to use Rubygem based libraries in a plugin

• How to access host components in Ruby

• How to use the execution result• Sinatra in Confluence ;-)

Example JRuby plugin

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• The plugin can’t be written in Ruby! • Use the Ruby runtime• Development workflow bonus: dynamic reloading!• The overhead of adding the runtime and providing

Java glue code makes this only feasible for high value use cases :(

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Let’s recap

• Scala is a great alternative when developing an Atlassian plugin

• JRuby is powerful, makes developing in a dynamic language possible but requires more work and custom Java adapter code

• Java interoperability needs to be well understood in both cases

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Conclusion

#atlascamp

TAKE-AWAYS

The power of the Atlassian plugin framework allows

you to build your plugins the way you want and

Java doesn’t have to be the limit.

“”

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Thank you!

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