Lift Comet Chat Example

I recently did a presentation on Lift. A lot of the materials were drawn from:David Pollak’s Java One Presentation and Marius Danciu’s Presentation. I posted the slides at linkedin. I wanted to demostrated Lift’s strength. So I created a quick Comet Chat example based on David’s code.

There were quite a few requests on the code. Instead of just create a zip file to let you download it. I’m going to walk you through how to build it.

First you need maven2. You can’t do anything with lift without it. You can download it here Come back to this when you finish downloading and installing it. You need to be able to issue mvn command.

Next we are going to create the lift project. For this one, we’ll use the lift-archetype-blank archetype.

mvn archetype:generate -U \
  -DarchetypeGroupId=net.liftweb \
  -DarchetypeArtifactId=lift-archetype-blank \
  -DarchetypeVersion=1.0 \
  -DremoteRepositories=http://scala-tools.org/repo-releases \
  -DgroupId=demo.app \
  -DartifactId=chat \
  -Dversion=1.0-SNAPSHOT

After tons of maven stuff scrolling through your screen. When it’s done. A directory called chat will be created. Now let’s run it to make sure it works.

cd chat
mvn jetty:run

If this part worked. You’ll see jetty up and running at port 8080. You can check it out by going to http://localhost:8080 on your browser.

Hit Ctrl-C and stop the running jetty. Onward to the next part.

Now you need to create src/main/scala/demo/app/comet/Chat.scala

package demo.app.comet

import scala.actors.Actor
import Actor._
import net.liftweb._
import http._
import js._
import SHtml._
import JsCmds._

case class Messages(msgs: List[String])

object ChatServer extends Actor with ListenerManager {
  private var msgs: List[String] = Nil

  protected def createUpdate = Messages(msgs)

  override def highPriority = {
    case s: String if s.length > 0 =>
      msgs ::= s
      updateListeners()
  }

  this.start
}

class Chat extends CometActor with CometListenee
{
  private var msgs: List[String] = Nil

  def render =


      {
        msgs.reverse.map( m =>
{m}

)
      }
      

      {
        ajaxText("", s => {ChatServer ! s; Noop})
      }
    

  protected def registerWith = ChatServer

  override def highPriority = {
      case Messages(m) =>
        msgs = m ;
        reRender(false)
  }
}

That takes care of the code. You now have to include it in the view. To do this, edit src/main/webapp/index.html

The default file looks like below

<lift :surround with="default" at="content">
                <h2>Welcome to your project!</h2>
                <p><lift:helloWorld.howdy /></p>
</lift:surround>

Replace it with

<lift :surround with="default" at="content">
                <lift:comet type="Chat" />
</lift:surround>

That’s it. Now issue

mvn jetty:run

And you’ll see the Comet Chat in all its glory.