Liftweb 1.1 and Google AppEngine

With only minor modifications, I have repeated Joe Kutner's installation of Liftweb on AppEngine. I'm running OS/X, so I started by using macports to install maven2. I saw that Java App-Engine was just updated to 1.3.1, so that was installed and I adjusted my APPENGINE_HOME and M2_HOME in .profile. The latest liftweb version is 1.1-M8, so I'll try that one.

Now that I know I have updated libraries, I generated a liftweb project with:

mvn archetype:generate -U -DarchetypeGroupId=net.liftweb

-DarchetypeArtifactId=lift-archetype-blank -DarchetypeVersion=1.1-M8

-DremoteRepositories=http://scala-tools.org/repo-releases

-DgroupId=com.folkertsfotografie. rlftest -DartifactId= rlftest

Rather than using -Dversion=1.0-SNAPSHOT, I entered a version of 1.1-M8 when prompted in maven. As usual, then next commands were cd rlftestl and a quick mvn jetty:run to see that http://localhost:8080/ was working. As an eclipse user, I added mvn eclipse:eclipse. So far, so good. The simple helloword application came up normally under the jetty installed with liftweb.

To integrate with AppEngine, I just added the boilerplate appengine-web.xml in my WEB-INF directory. The contents are:

<?xml version="1.0" encoding="utf-8"?>

<appengine-web-app xmlns="http://appengine.google.com/ns/1.0">

<application>rlftest>

<version>3</version>

<system-properties>

<property name="in.gae.j" value="true" />

</system-properties>

<sessions-enabled>true</sessions-enabled>

<static-files>

<exclude path="/**" />

</static-files>

</appengine-web-app>

With that done, I built the war file with mvn package. To run that war file under AppEngine, just type

$APPENGINE_HOME/bin/dev_appserver.sh target/rlftest-1.1-M8.

That also worked, I could see http://localhost:8080/. Finally, I published this to appsite with $APPENGINE_HOME/bin/appcfg.sh update target/rlftest-1.1-M8.

With that done, I browsed my AppEngine control panel and tested that the hello world application. It worked without a hitch. Now, I can get back to learning liftweb and Scala. It isn't at all clear to me how liftweb and datastore will work together, but I'll just have to burn that bridge when I get to it. So thanks Joe, you have been a great help getting me started with Lift.

REST and application evolution

REST turns out to be the key to allowing software to be upgraded without breaking applications. The idea is pretty simple,you agree on the small number of REST verbs. You then have interfaces that are specified by URL and a version number (perhaps part of URL). You then allow clients to specify their version number in a request.

This is discussed in a couple of InfoQ talks. Alex Antonov gave Case Study: RESTful Web Services at Orbitz. He shows how Protocol Buffers allow for efficient (he claims 7 times faster than SOAP) and flexible message passing using HTTP. Protocol Buffers is an open source HTTP messaging protocol developed by Google. The exchanged data uses protobuf.

Steve Vinoski gives a great talk on RPC and its fundamental flaws. He was an expert in CORBA in the 90's and he has recently moved to REST and Erlang. He is quite convinced that functional programming is the future and that imperative languages, such as Java and C# are based upon a the wrong model of distributed programming.

These talks dovetail nicely with Kirk Wylie's earlier InfoQ talk, Restful approaches to financial systems.