Devoxx 2009: The Lift Framework

Whistle-‐stop
tour
of
the
Li#
web
framework
and

demonstra:ng
why
the
real-‐:me
web

should
ma=er
to
you

www.devoxx.com

Agenda

!  Overview
of
Scala

!  Li#’s
Ra:onale

!  The
real-‐:me
web

!  Li#’s
awesome
feature
set

!  Why
Scala
makes
Li#
possible

www.devoxx.com

About
Me

!  Project
commi=er
on
Li#

!  Manufacturing
and
marke:ng
automa:on
is

my
day-‐job
(industrial
systems)

!  Whole
raH
of
experience
with
both
dynamic

and
sta:c
languages

!  Desktop
and
Web
applica:on
development

www.devoxx.com

!  Coding
Scala
and
LiH
since
end
of
2007

What
is
Scala?
(10,000
foot
view!)

!  Scala
is
func:onal

!  Scala
is
object
orientated

!  Scala
is
mul:-‐paradigm!
OO
and
FP
hybrid...

!  Designed
by
Mar:n
Odersky
(Java
generics)

!  Runs
as
fast
as
na:ve
Java
code

!  Fully
interoperable
with
exis:ng
Java
libraries

www.devoxx.com

!  More
type-‐safe
than
Java

Scala
in
the
wild?

www.devoxx.com

Scala
in
breif….

!  What
follows
is
an
overview
of
core
Scala

language
features

www.devoxx.com

Immutability

val example = “Devoxx”

!  Immutable
values
are
assigned
with
the

“val”
keyword

!  Immutability
is
your
long-‐lost
friend:

!  
No
need
to
synchronise

!  
Never
need
to
copy
vars
“just
in
case”

!  
Great
for
hash
keys

www.devoxx.com

!  Be=er
for
garbage
collector

Case
Classes

case class Foo(bar: String, baz: List[Int])

!  Func:onality
you
get
for
free:

!  
“new”
keyword
is
redundant

!  
bar
and
baz
proper:es
(immutable
by
default)

!  
toString,
hashCode,
and
equals
et
al

!  
Pa=ern
matching
with
parameter
extrac:on

www.devoxx.com

Singletons

object ChatServer extends Actor

!  ChatServer
is
a
singleton

!  One
instance
per
classloader

!  Can
be
passed
as
parameter…
it’s
an
instance

www.devoxx.com

Composi:on
with
Traits

!  Finely-‐grained
aggrega:on
of
func:onality

!  Mul:ple-‐inheritance
without
diamond
problem[1]

!  Extensively
used
in
Li#

object sally extends Person(“Sally”)
with Female
with Runner

def womansRun(who: Female with Runner)
www.devoxx.com

//=> womansRun(sally)
[1]
h=p://en.wikipedia.org/wiki/Diamond_problem

Func:on
Passing

!  Encapsulates
logic
concisely

!  Wildcard
shorthand
keeps
things
simple

!  Func:ons
are
instances
that
can
be
passed

// make x a function that lower cases input
val x: (String) => String = (str) => str.toLowerCase
www.devoxx.com

// alter the request encoding
LiftRules.early { _.setCharacterEncoding(“UTF-8”) }

Pa=ern
Matching

!  Match
against
case
classes

!  
Parameter
extrac:on

!  
Great
for
message
/
event
handling

!  
Test
against
parameters:
case Person(name, 35) =>

!  Declara:ve
expression
of
logic

case Messages(m) => msgs = m
www.devoxx.com

case s: String if s.length > 0 => msgs ::= s

XML
Literals

!  XML
is
ﬁrst-‐class

!  Ripe
for
templa:ng
abuse!

!  Very
handy
for
development
but
Li#
provides

strong
abstrac:ons
for
templates

val links = (“Link A”, http://…) ::
(“Link B”, “http://…”) :: (“Link C”, https://…) :: Nil
www.devoxx.com

val myLinkList =
<ul>{ links.flatMap({case (name,url) =>
<li><a href={url}>{name}</a></li>}) }
</ul>

Actors

!  Being
“real-‐:me”
means
events

!  Lightweight
concurrency
model

!  With
very
nice
syntax

!  Implemented
as
a
library!

object DevoxxActor extends Actor { …… }
case class Talk(name: String)
www.devoxx.com

// asyncronusly send the talk message to the actor
DevoxxActor ! Talk(“Lift web framework”)

What
is
LiH?

!  Web
framework
wri=en
in
Scala

!  3
years
old,
founded
by
David
Pollak

!  Leverages
the
best
of
Scala
language
features

!  Takes
the
best
ideas
from
other
frameworks

!  Makes
real-‐:me
web
applica:ons
accessible

!  Massively
scalable

www.devoxx.com

Why
another
framework?

!  Developers
needn't
be
plumbers

!  Uniﬁes
the
best
of
other
framework
concepts

!  
Granular
sessions
and
security
a
la
Seaside

!  
Flash-‐to-‐bang
produc:vity
a
la
Rails

!  
Designer
friendly
templates
a
la
Wicket

!  Advanced
features
like
comet
work
OOTB

www.devoxx.com

!  Tough
to
be
truly
real-‐:me
with
exis:ng
tech

Web
Beginnings

!  Very
person
-‐>
machine
aﬀair

!  Primary
uses:

!  
Shopping

!  
Banking

!  
CRUD
opera:ons

!  56k
modems
(yikes!)

www.devoxx.com

Web
2.0

!  Behaviour
shiH
-‐>
more
social

!  Diﬀerent
usage
models:

!  
Person
-‐>
Machine
-‐>
Machine
(mashups)

!  
Person
-‐>
Person
(Facebook,
Twi=er)

!  
Machine
-‐>
Machine
-‐>
Person
(micro-‐formats)

!  Internet
becomes
society
cornerstone

www.devoxx.com

Real
Time
Web

!  Users
demand
instant
gra:ﬁca:on

!  Peer-‐to-‐peer
news
/
informa:on
streams

!  Business
informa:on
in
constant
ﬂux

!  Online
interac:ve
games

!  Real
Time
Web
is
the
next
evolu2onary
step...

www.devoxx.com

View
First

!  Its
not
MVC

!  Your
typical
page
has
more
than
a
single
piece

of
dynamic
content

!  Code
in
the
view
usually
means
some
“seep”

of
business
logic:
thus,
NO
code
in
the
view

!  Only
well-‐formed
XHTML;
no
string

replacement
–
e.g.
{{myvar}}

www.devoxx.com

!  Designer
friendly
dynamic
content
markup

Snippets

!  A
“snippet”
in
Li#
represents
a
collec:on
of

applica:on
logic

!  One
snippet
can
be
called
on
n
number
of

pages,
n
number
of
:mes

!  A
snippet
is
a
normal
Scala
class
or
object:

there
is
no
black
magic

www.devoxx.com

!  Lookup
via
reﬂec:on
or
manual
wiring

What
a
bind…

class Example {
def nameForm(xhtml: NodeSeq) = {
var name = “”
def doSubmit { println(“Submitted…”); }
bind("f", xhtml,
"name" -> SHtml.text(name, name = _),
"submit" -> SHtml.submit(doSubmit _)
)
}
}
<lift:example.name_form>
<p><f:name /></p>
www.devoxx.com

<p><f:submit /></p>
</lift:example.name_form>

Security

!  Page
elements
have
session
speciﬁc
opaque

GUIDs
to
reference
server
components

(impossible
to
do
CSRF[1])

<input name=“F677071620957IFD” type=“text” />

!  Callback
func:ons
also
use
similar
GUIDs
so

that
sensi:ve
IDs
etc
are
not
exposed

www.devoxx.com

/somepath?F677071620979LIK=_

[1]
h=p://en.wikipedia.org/wiki/Cross-‐site_request_forgery

Site
Map

!  
Declara:ve
and
granular
defini:on
of
page

and
UI
access
rules

!  Enforced
long
before
the
page
content
is

processed
or
rendered
–
its
very
fast.

!  Can
generate
site
menus
even
with
complex

rules
on
what
different
users
see

www.devoxx.com

!  Unified
access
control
model

Persistence

!  Li#
includes
“Mapper”
which
is
a
lightweight

ORM
of
similar
design
to
Ac:veRecord
in
Rails

!  Use
any
backend
persistence
system
you

want
(Hibernate,
JPA
etc)

!  Write
custom
back-‐ends
using
Li#
Record
–

provides
OOTB
valida:on
and
CRUD

seman:cs;
you
provide
the
implementa:on

www.devoxx.com

REST
and
WebServices

!  REST
via
state(full/less)
dispatching

!  Declara:ve
rules
for
URI
-‐>
handler
dispatch

!  LiH
has
awesome
support
for
JSON:

!  
Slick
DSL
for
construc:on
/
parsing

!  
~300
:mes
faster
than
Scala
JSON
parser

!  
Faster
deseriliza:on
than
Java

www.devoxx.com

!  Na:ve,
ﬁrst-‐class
XML
support
in
Scala

Technology
Support

!  AMQP

!  Tex:le

!  XMPP

!  OpenID

!  JTA

!  PayPal

www.devoxx.com

!  …and
lots
more!

Summary

!  Scala’s
object
model
is
a
superset
of
Java’s

!  Scala
traits:
powerful
and
granular
composi:on

!  Scala
is
syntac:cally
simpler
than
Java
or
Ruby

!  Scala’s
design
led
to
Li#’s
design

!  Li#
makes
the
real-‐:me
web
simple

!  Li#
is
the
culmina:on
of
many
great
ideas

www.devoxx.com

Devoxx 2009: The Lift Framework

Devoxx 2009: The Lift Framework

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