Reactive Web Programming with Lift

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Lucas Satabin satabin@informatik.tudarmstadt.

1 Lucas Satabin Reactive Web Programming with Lift July 7 th 2010

2 Reactive Web Programming with Lift 2 Lift Books Available April 2011 Early preview: Free online version:

3 Reactive Web Programming with Lift 3 Lift Tutorials The lift maven archetypes! /lift-web-framework-scala-pollack Official website:

4 Lift is the only new framework in the last four years to offer fresh and innovative approaches to web development. It's not just some incremental improvements over the status quo, it redefines the state of the art. If you are a web developer, you should learn Lift. Even if you don't wind up using it everyday, it will change the way you approach web applications. Michael Galpin, Developer, ebay

5 Reactive Web Programming with Lift 5 Lift What is Lift? A framework for writing web applications in Scala Solves elegantly many common problems encountered in web application development Includes the best ideas from all other web frameworks! (Rails, Django, Wicket, ) Write reactive web applications quickly... Once you understood the concepts...

6 Reactive Web Programming with Lift 6 Architecture

7 Reactive Web Programming with Lift 7 Lift Configuration Application configuration in a Boot class Define the website structure Define the data model Configure internationalization, encoding,

8 Reactive Web Programming with Lift 8 Pros View First No logic in the view Unlike JSP, ASP, Supported by standard HTML tools Designer can work without scala development environment Written in Scala Uses Maven

9 Reactive Web Programming with Lift 9 Cons Still HTML to write Written in Scala Uses advanced features Uses Maven But now use of SBT (Simple Build Tool) possible SBT however is also in Scala... Don't be afraid of this!

10 Reactive Web Programming with Lift Scala (Extremely) Short Introduction

11 Reactive Web Programming with Lift 11 A Powerful Language Full support for object-oriented features Also a functional language (higher-order functions, immutable data types,...) Powerful type system (type inference, generics, covariance, ) Mixin composition using traits Compiles to Java bytecode or.net CLR Full compatibility with Java libraries More at

12 Reactive Web Programming with Lift 12 Some Scala Syntax class MyClass(val param1: Int, var param2: String) { def m1(i: Int) = println(i) } def m2(): Boolean = { if(param1 > 0) true else false } object MyObject { def main(args: Array[String]) { val c = new MyClass(2, "test") c.m2() c m1 5 } }

13 Reactive Web Programming with Lift 13 XML in Scala Native support for XML XPath integration val page = <html> <head> <title>example</title> </head> <body> <h1>scala rocks!</h1> </body> </html>

14 Reactive Web Programming with Lift 14 Actor Programming case class Ping(source: Actor) case class Pong() Concurrent programming model No shared memory Message passing style object PingActor extends Actor { def act = { loop { receive { case Ping(source) => source! Pong } } } } PingActor! Ping(actor)

15 Reactive Web Programming with Lift Lift The first application

16 Reactive Web Programming with Lift 16 Create a new Application Run maven and voilà! $ mvn archetype:generate -U \ -DarchetypeGroupId=net.liftweb \ -DarchetypeArtifactId=lift-archetype-blank \ -DarchetypeVersion=2.0 \ -DgroupId=ctfda -DartifactId=firstApp \ -Dversion=0.0.1-SNAPSHOT Other archetypes available (with user management, JPA,...)

17 Reactive Web Programming with Lift 17 Define The View default.html <html> <head> <title>my first Lift Application</title> </head> <body> <lift:bind name="content" /> </body> </html> index.html <lift:surround with="default" at="content"> <h1>welcome!</h1> <lift:helloworld.sayhello> Welcome to Lift at <hello:date />! </lift:helloworld.sayhello> </lift:surround>

18 Reactive Web Programming with Lift 18 The Snippet part HelloWorld.scala package ctfda.firstapp.snippet import java.util.date import scala.xml.nodeseq import net.liftweb.util.helpers._ <lift:helloworld.sayhello> class HelloWorld { def sayhello(html: NodeSeq): NodeSeq = bind("hello", html, "date" -> new Date().toString) } <hello:date />

19 Reactive Web Programming with Lift 19 And Voilà! $ mvn jetty:run A lot of stuffs [INFO] Starting scanner at interval of 5 seconds.

20 Reactive Web Programming with Lift 20 Adding New Pages All accessible pages configured in the Boot class The SiteMap describes the web application structure

21 Reactive Web Programming with Lift Session Management Problems and Solution

22 Reactive Web Programming with Lift 22 Session Management A general (and ubiquitous) problem Why do I need sessions? HTTP is stateless it makes everything difficult Where should sessions be managed? On the client side On the server side On both sides?

23 Reactive Web Programming with Lift 23 Sessions in Lift Lift is a stateful framework! LiftSession NOT build on top of HttpSession Implemented with an actor managing the lifecycle of sessions Two main classes: SessionVar and RequestVar No direct reference to the session Type-safe access to the data Default value Clean up mechanism

24 Reactive Web Programming with Lift 24 Use of Session Variables class HelloWorld { object name extends SessionVar("anonymous") def identify(html: NodeSeq) = Set the session value bind("id", html, "name" -> text("", n => name.apply(n)), Do nothing "submit" -> submit("change name", () => ())) def sayhello(html: NodeSeq) = Get the session value bind("hello", html, "name" -> <b>{name.is}</b>, "date" -> (new java.util.date).tostring) } <lift:surround with="default" at="content"> <h1>welcome!</h1> <lift:helloworld.sayhello> Welcome to Lift <hello:name /> at <hello:date />! </lift:helloworld.sayhello> <p /> <lift:helloworld.identify form="post"> Please give your name <br /> <id:name /> <id:submit /> </lift:helloworld.identify> </lift:surround>

25 Reactive Web Programming with Lift 25 Session Variable Result

26 Reactive Web Programming with Lift Persistence

27 Reactive Web Programming with Lift 27 The Mapper Component Original persistence framework Closely tied to JDBC Based on two basic traits Mapper per-instance features MetaMapper global operations Inheriting from these traits makes the entity persistent Easy to use for Database Sharding (do you remember?) CRUD features and views using the CRUDify trait

28 Reactive Web Programming with Lift 28 New Entities class Post extends LongKeyedMapper[Post] with IdPK { def getsingleton = Post } object title extends MappedString(this, 140) object content extends MappedString(this, 5000) object author extends LongMappedMapper(this, Author) object Post extends Post with LongKeyedMetaMapper[Post] class Author extends MegaProtoUser[Author] { def getsingleton = Author } This is a really nice class! object Author extends Author with MetaMegaProtoUser[User]

29 Reactive Web Programming with Lift 29 Schemifying the Model package bootstrap.liftweb class Boot { def boot {... val vendor = new StandardDBVendor("org.h2.Driver", "jdbc:h2:lift_proto.db;auto_server=true") LiftRules.unloadHooks.append(vendor.closeAllConnections_! _) DB.defineConnectionManager(DefaultConnectionIdentifier, vendor) } } // add entities to the schemifier Schemifier.schemify(true, Log.infoF _, Post, Author)

30 Reactive Web Programming with Lift 30 Alternative to Mapper Record framework Refactorization of Mapper Backing-store agnostic JDBC JPA XML file Integration of JPA Support for NoSQL (CouchDB and MongoDB)

31 Reactive Web Programming with Lift Ajax and Comet Reactive Web Applications

32 Reactive Web Programming with Lift 32 Classic Web Application

33 Reactive Web Programming with Lift 33 Ajax Application

34 Reactive Web Programming with Lift 34 Lift and Ajax Uses jquery ( No differences in the HTML file Helpers to generate the Ajax elements Object net.liftweb.http.shtml No javascript to write in most cases! Makes heavy use of scala closures and first-class functions

35 Reactive Web Programming with Lift 35 Comment a Post: the Model class Comment extends LongKeyedMapper[Comment] with IdPK { def getsingleton = Comment } object author extends MappedPoliteString(this, 30) object date extends MappedDateTime(this) object content extends MappedText(this) object post extends LongMappedMapper(this, Post) object Comment extends Comment with LongKeyedMetaMapper[Comment] class Post extends LongKeyedMapper[Post] with IdPK with OneToMany[Long, Post] { // unchanged... object comments extends MappedOneToMany(Comment, Comment.post, OrderBy(Comment.id, Ascending)) }

36 Reactive Web Programming with Lift 36 Comment a Post: the Snippet def comments(html: NodeSeq): NodeSeq = { val id = S param "id" map (_.tolong) open_! var author = "" var content = "" Generates all the Ajax code for us! bind("comment", html, "newauthor" -> text("anonymous", a => author = a), "newcontent" -> textarea("", t => content = t), "submit" -> ajaxsubmit("post comment!", () => { savecomment(id, author, content) SetHtml("comments", comments(html))}, "list" -> bindcommentlist _))} <div id="comments"> <h3>new comment</h3> <lift:form> <table> <tr><td>name</td><td><comment:newauthor /></td></tr> <tr><td>comment</td><td><comment:newcontent /></td></tr> <tr><td><comment:submit /></td></tr> </table> </lift:form>  </div>

37 Reactive Web Programming with Lift 37 Comet

38 Reactive Web Programming with Lift 38 Comet: Principles Programming technique Allows a server to send messages to clients Better than classical polling Different approaches for implementation Hidden IFrame Long polling Alternative: HTML5 server-sent DOM events

39 Reactive Web Programming with Lift 39 Comet in Lift Different implementations Sleeping threads Does not scale! Non-Blocking IO Jetty Continuations when running in Jetty Future: Servlet 3.0 Suspended Requests Actor driven development CometActor does almost everything for you!

40 Reactive Web Programming with Lift 40 Comet in Lift: Ideas A dispatcher actor object Publish/Subscribe style Comet actors register with this actor A Comet actor One instance per type per session Update the client content

41 Reactive Web Programming with Lift 41 Comet Flow in Lift Gets a Comet request Checks the CometActors to see if there are any messages. If no messages, request suspended, no response to client When your Comet actor receives a message, response is calculated, request resumed Response sent to client

42 Reactive Web Programming with Lift 42 Comet Comments case class AddComment(postId: Long, author: String, date: Date, content: String) object Blog {... def comments(html: NodeSeq): NodeSeq = {... bind("comment", html, AttrBindParam("cometName", S param "id" open_!, "name"), "newauthor" -> text("anonymous", a => author = a), "newcontent" -> textarea("", t => content = t), "submit" -> ajaxsubmit("post comment!", () => { Commenter! AddComment(id, author, new Date, content) Noop })) } }

43 Reactive Web Programming with Lift 43 Commenter Actor object Commenter extends LiftActor with ListenerManager { var postid = 0L def createupdate = postid override def lowpriority = { case AddComment(postId, author, date, content) => // save the comment... // save the post id this.postid = postid updatelisteners() } }

44 Reactive Web Programming with Lift 44 Comet Actor class Comments extends CometActor with CometListener { override def shouldupdate = { case id: Long if id == name.map(_.tolong).open_! => true case _ => false } def registerwith = Commenter val postid = S.param("id").map(_.toLong).openOr(0L) var comments: List[Comment] = getcomments private def getcomments = Comment.findAll( By(Comment.post, postid), OrderBy(Comment.date, Descending)) } override def lowpriority = { case id: Long => comments = getcomments rerender(false) case _ => Log info "other message" } def render = bindcomments

45 Reactive Web Programming with Lift Security

46 Reactive Web Programming with Lift 46 Authentication Using the MegaProtoUser class Allows use of Realms For example Single Sign-On Abstractions for Basic and Digest HTTP Authentication Hierarchical role structure

47 Reactive Web Programming with Lift 47 XSS Attacks Nonce generated each time a form is loaded Avoid scripting Resistant to the OWASP top 10 vulnerabilities including XSS XSRF parameter tampering

48 Reactive Web Programming with Lift 48 Resources Access Strong control over accessible resources Only pages added to the SiteMap WEB-INF and template-hidden directories never directly accessible Use of container access control Configuration in web.xml Works on all Servlet containers

49 Reactive Web Programming with Lift To be continued...

50 Reactive Web Programming with Lift 50 What Else? Support for RESTful web services A lot of helpers JSON parser Checks Integration with OpenID XMPP (Jabber) Lucene Facebook

51 Reactive Web Programming with Lift 51 And Even More Widgets Calendar Table sorter Tree view Screens and Wizards

52 Reactive Web Programming with Lift Thank you for your attention Any questions?

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