I wrote a Java servlet that accessed the AbstractIterator class in the kotlin-runtime.jar library, and it worked fine.  It seems that the issue is that the Kotlin class isn't being compiled, or the resultant .class files are not being put in the same place as the Java files.

Per your request I've attached the project, although note that it assumes that the Google App Engine SDK is here:

  /Users/ian/java-libs/appengine-java-sdk-1.6.4.1

Here is the exception I get when I try to run it (note that it seems to work fine when I use a Java file that has the same class name, package, and functionality):

Apr 7, 2012 7:21:46 PM com.google.apphosting.utils.jetty.JettyLogger warn

WARNING: EXCEPTION

java.lang.ClassNotFoundException: testpack.TestServlet

at java.net.URLClassLoader$1.run(URLClassLoader.java:202)

at java.security.AccessController.doPrivileged(Native Method)

at java.net.URLClassLoader.findClass(URLClassLoader.java:190)

at java.lang.ClassLoader.loadClass(ClassLoader.java:306)

at com.google.appengine.tools.development.IsolatedAppClassLoader.loadClass(IsolatedAppClassLoader.java:176)

at java.lang.ClassLoader.loadClass(ClassLoader.java:247)

at org.mortbay.util.Loader.loadClass(Loader.java:91)

at org.mortbay.util.Loader.loadClass(Loader.java:71)

at org.mortbay.jetty.servlet.Holder.doStart(Holder.java:73)

at org.mortbay.jetty.servlet.ServletHolder.doStart(ServletHolder.java:242)

at org.mortbay.component.AbstractLifeCycle.start(AbstractLifeCycle.java:50)

at org.mortbay.jetty.servlet.ServletHandler.initialize(ServletHandler.java:685)

at org.mortbay.jetty.servlet.Context.startContext(Context.java:140)

at org.mortbay.jetty.webapp.WebAppContext.startContext(WebAppContext.java:1250)

at org.mortbay.jetty.handler.ContextHandler.doStart(ContextHandler.java:517)

at org.mortbay.jetty.webapp.WebAppContext.doStart(WebAppContext.java:467)

at org.mortbay.component.AbstractLifeCycle.start(AbstractLifeCycle.java:50)

at org.mortbay.jetty.handler.HandlerWrapper.doStart(HandlerWrapper.java:130)

at org.mortbay.component.AbstractLifeCycle.start(AbstractLifeCycle.java:50)

at org.mortbay.jetty.handler.HandlerWrapper.doStart(HandlerWrapper.java:130)

at org.mortbay.jetty.Server.doStart(Server.java:224)

at org.mortbay.component.AbstractLifeCycle.start(AbstractLifeCycle.java:50)

at com.google.appengine.tools.development.JettyContainerService.startContainer(JettyContainerService.java:196)

at com.google.appengine.tools.development.AbstractContainerService.startup(AbstractContainerService.java:239)

at com.google.appengine.tools.development.DevAppServerImpl.start(DevAppServerImpl.java:146)

at com.google.appengine.tools.development.DevAppServerMain$StartAction.apply(DevAppServerMain.java:189)

at com.google.appengine.tools.util.Parser$ParseResult.applyArgs(Parser.java:48)

at com.google.appengine.tools.development.DevAppServerMain.<init>(DevAppServerMain.java:128)

at com.google.appengine.tools.development.DevAppServerMain.main(DevAppServerMain.java:104)

at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)

at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:39)

at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:25)

at java.lang.reflect.Method.invoke(Method.java:597)

at com.intellij.rt.execution.application.AppMain.main(AppMain.java:120)

Yes, I can confirm that manually copying the class files across and running GAE from the command line as you suggest does work - yay progress! ;-)

But the question is: why isn't this working from within IDEA - since it was working with Java?  To start it I was just hitting the green "Play" button in IDEA ("Run 'AppEngine Dev'").

This seems to work fine when the source file is Java, it copies the compiled class files over to WEB-INF/classes as it should (I think it is configured in Project Structure -> Artifacts), so why wouldn't it be doing this for a Kotlin source file?