How to use sbt with Google App Engine?

Question

Has anybody tried to setup sbt to work with Google App Engine? I dream about using development server auto-reloading after source changes.

Answer 1

For a quick demo you can clone or download what I have done here.

A minimalistic sbt-appengine-plugin example from scratch

Clone the sbt-appengine-plugin from GitHub

 cd mystuff
 git clone git://github.com/Yasushi/sbt-appengine-plugin.git
 cd sbt-appengine-plugin
 sbt

Publish the plugin locally so that you can use it in your own projects

publish-local
exit

Create a directory for a new project

cd ..
mkdir sbt-appengine-plugin-test
cd sbt-appengine-plugin-test
sbt

Configure the new project

Project does not exist, create new project? (y/N/s) y
Name: sbt-appengine-plugin-test
Organization: com.example
Version [1.0]: 
Scala version [2.7.7]: 2.8.0.Beta1
sbt version [0.7.3]:
exit

Tell sbt about the plugin you want to use

mkdir project/build
mkdir project/plugins
nano project/build/project.scala

project.scala

import sbt._

class AppengineTestProject(info: ProjectInfo) extends AppengineProject(info)

nano project/plugins/plugins.scala

plugins.scala

import sbt._

class Plugins(info: ProjectInfo) extends PluginDefinition(info) {
  val a = "net.stbbs.yasushi" % "sbt-appengine-plugin" % "1.1-SNAPSHOT"
}

Add a very simple servlet

mkdir -p src/main/scala/com/example
nano -w src/main/scala/com/example/HelloWorld.scala

HelloWorld.scala

package com.example;

import javax.servlet.http.{HttpServlet, HttpServletRequest, HttpServletResponse}

class HelloWorld extends HttpServlet {
  override def doGet(request: HttpServletRequest, response: HttpServletResponse$
    response.setContentType("text/plain")
    response.getWriter.println("Hello, world")
  }
}

Add some more configuration files

mkdir -p src/main/webapp/WEB-INF
nano -w src/main/WEB-INF/web.xml

web.xml

<?xml version="1.0" encoding="ISO-8859-1"?>
<web-app 
   xmlns="http://java.sun.com/xml/ns/javaee" 
   xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
   xsi:schemaLocation="http://java.sun.com/xml/ns/javaee http://java.sun.com/xm$
   version="2.5">
  <display-name>sbt-appengine-plugin usage example</display-name>
      <servlet>
    <servlet-name>helloworld</servlet-name>
    <servlet-class>com.example.HelloWorld</servlet-class>
  </servlet>
      <servlet-mapping>
    <servlet-name>helloworld</servlet-name>
    <url-pattern>/</url-pattern>
  </servlet-mapping>
</web-app>


nano -w src/main/WEB-INF/appengine-web.xml

appengine-web.xml

<appengine-web-app xmlns="http://appengine.google.com/ns/1.0">
<!-- Replace this with your application id from http://appengine.google.com -$
  <application>hello-world</application>
  <version>1</version>
</appengine-web-app>

And finally run sbt and start the project

sbt

update
dev-appserver-start

Point your browser to http://localhost:8080/ and you should see Hello, world

dev-appserver-stop

To watch for changes in source files I have experimented a little with ~prepare-webapp after starting the server, but I haven't gotten it working properly.

Answer 2

Here is an sbt-appengine-plugin on Github that I'm trying to get to work right now. I will post any progress.

Answer 3

You will find an example by the author of the plugin here: http://gist.github.com/377611

Especially in the plugins configuration, the setting of 1.1-SNAPSHOT (mentioned above) or 2.1-SNAPSHOT (mentioned in the sbt-apppengine-plugin README) did not work.

The example shows:

import sbt._

class Plugins(info: ProjectInfo) extends PluginDefinition(info) {
    val appenginePlugin = "net.stbbs.yasushi" % "sbt-appengine-plugin" % "2.0" from "http://github.com/downloads/Yasushi/sbt-appengine-plugin/sbt-appengine-plugin-2.0.jar"
}

And this worked for me.

Answer 4

Here's a template project using sbt + appengine which can be used to get started:

https://github.com/mtkopone/sbt-scalatra-appengine-template

Also, instead of having to publish the sbt-appengine-plugin locally, you can use the following in Plugins.scala:

import sbt._
class Plugins(info: ProjectInfo) extends PluginDefinition(info) {
  lazy val appEngine = "net.stbbs.yasushi" % "sbt-appengine-plugin" % "2.1" 
    from "http://cloud.github.com/downloads/Yasushi/sbt-appengine-plugin/sbt-appengine-plugin-2.1.jar"  
}

Answer 5

I wrote an example application describing how to set up a development environment and create an application using SBT and app engine. It also includes instructions on setting up JRebel to get the auto reloading you dream of.

See http://jeremys-scala-example.appspot.com/

It is for SBT 0.7 so its a little out of date.

Answer 6

There is now a new version of the sbt-appengine plugin which works with newer versions of SBT (0.10+) at https://github.com/sbt/sbt-appengine. There's also a trivial sample app using it at https://github.com/sbt/sbt-appengine.

I just converted a project that was created with Eclipse:

• Move scala files from src/ to src/main/scala.
• If you have java files, move them from src/ to src/main/java.
• Move war/ to src/main/webapp.
• If you have other files that should end up in WEB-INF/classes, put them in src/main/webapp/WEB-INF/classes/.