A First Look At Scala On Google App Engine

1. Scala on Google App Engine
Eishay Smith
KaChing

2. Who Am I
kaChing - Rocking the inventing world !
Scala @ LinkedIn
Blogging http://www.eishay.com
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http://github.com/eishay/newspipes
kaChing Twitter Bot
http://code.google.com/p/kaching-twitter/
Presented:
"Absorbing Scala into Java Ecosystem"

3. Google App Engine
Run your web apps on Google's infrastructure.
Easy to build, easy to maintain, easy to scale.
Now with Java
And a host of languages that run on the JVM
JRuby, Groovy, Scala, Jython, ...

4. Tooling
Eclipse
Great GAE support for Java with GWT and JDO
Some problems coming to Scala
Ant
All you need
Longer development/test cycle
Oher IDEs
Netbeans
IDEA

5. Scala and Google Web Toolkit (GWT)
GWT - quickly build and maintain complex & performant
JavaScript front-end apps written in Java (NOT Scala)
GWT actually compiles the Java source code
A GWT class should not reference any Scala class
Still, GWT is super cool, use it!
You can still have 99% of the server side in Scala
Use Java only for service interfaces
Use Scala for the rest

6. Use interface
To buffer between Scala and GWT code

7. Implement using the best language

8. Use From GWT

9. One XML to bind them all

10. Regular HttpServlet

11. With Regular Binding

12. Scala @ JDO: Spelling it out
Similar to the Java JDO
Using the same annotations

13. Scala @ JDO: ANT
The ORM enhancer works on the class files
Bytecode instrumentation
Does not matter if its Java or Scala

14. Scala @ JDO: Eclipse Support
Not really working since the IDE is looking for Java
source files to instrument
The solution is to use Eclipse Builders
Have the ANT JDO builder building after compilation
Provide an appengine.sdk path to the jar Eclipse use

15. More Limitations
Same limitations as in Java
IO libraries
Threading
Can't open new threads => Actors in a same thread mode
Lift on a single threaded Actor is happy

16. Building
Scala
Scalac knows
how to read
java code !
Needed for
circular
dependencies.

17. We Are Hiring !