How to integrate
your applications
with today‘s
technology trends
RESTful Web Services
in VA Smalltalk
Joachim Tuchel
www.objektfabrik.de
© 2009 by Joachim Tuchel

Agenda
• About me and objektfabrik
• „Classic“ Web Services
• RESTful Web Services: What‘s different?
• RESTful Web Services with VA Smalltalk
• DEMO: REST Clients & Server
• Questions

About me
• Founder and director of objektfabrik
• Business Informatics (Banking)
• Smalltalk since 1996
(VA Smalltalk,VisualWorks and Squeak)
• Java since 2004
• jtuchel@objektfabrik.de

About objektfabrik
• Founded 1999 in Ludwigsburg, Germany
• Training, Consulting, Professional Services
• Application and System architecture
• Software Development in Smalltalk, Java,
Ruby and Objective-C
• Instantiations Business Partner since 2006

Training offerings
• Object Technology Basics
• Smalltalk Basics
• VA Smalltalk Application Development
• Advanced VA Smalltalk workshops
(Packaging, Config Management, SUnit...)
• New in 2009: Seaside

Web Services
and VA Smalltalk

Web Services
• Uses HTTP/S POST for transport
• in theory uses any transport protocol
• XML Messages
• SOAP-Envelopes
• Namespaces
• Many standards / schemas available

Web Services
• W3C Standard
• Huge set of domain/industry specific and
vertical (cross industry) standards (WS-*)
• Large selection of tools and vendors
• „Enterprise integration technology“

Web Services and VA
Smalltalk
• Supported by VA Smalltalk since V 5.5
• Based on Server Smalltalk
• Constantly improved in 6.x, 7.x and 8
• Expose a Smalltalk method as a service
• Consume a service in Smalltalk

What‘s wrong with
Web Services
• Heavy weight standard
• One size fits all (by being large enough)
• Can be very complicated to deploy and
debug
• Very complex XML structures
• Way too heavy for simple jobs

RESTful Web Services

RESTful Web Services
• REST = Representational State Transfer
• What is it?
• Not a standard
• It‘s an architecture
• Simplicity and Reuse of existing Standards
like the HTTP (=Protocol) are design goals

REST is everywhere
• Amazon Web Services
• Simple Storage System (S3)
• SimpleDB - SQL - like Database
• eBay Shopping APIs
• PayPal

REST is everywhere
• Google REST APIs
• Search, Blogger, Maps, Analytics...
• Yahoo! REST APIs
• Finance, YQL, Travel, Weather...
• Twitter, Technorati, all over „Web 2.0“
• Apache CouchDB

REST is everywhere
• REST is part of „The Web“ today
• REST is used for
• Integration
• Distribution
• Scaling
• Mashups

Basic Concepts

Basic Concepts
• RESTful Web Services are about Resources,
not about Services (operations)

Basic Concepts
• RESTful Web Services are about Resources,
not about Services (operations)
• Addressability: Every Resource has a uniform
name = URI

Basic Concepts
• RESTful Web Services are about Resources,
not about Services (operations)
• Addressability: Every Resource has a uniform
name = URI
http://myhost/users/joachim/todolists...

Basic Concepts
• RESTful Web Services are about Resources,
not about Services (operations)
• Addressability: Every Resource has a uniform
name = URI
http://myhost/users/joachim/todolists...
• Statelessness: Server doesn‘t save any
application state ➠ Scalability

Basic Concepts
• Operations defined in HTTP standard
• Create: POST a new resource
• Read: GET a resource
• Update: PUT a resource
• Delete: DELETE a resource
• References to objects are IDs or hyperlinks

What‘s a Resource?
• •
Customer Database Transaction
• •
Purchasing Order Flight Booking
• •
Line Item Message
• •
Hotel Room Dataset (RDB/OODB)
• •
Hotel Room Reservation any entity we deal with in
our systems
• User Account

What‘s a Resource?
• Not necessarily a Business Object!
• Not all aspects need to be transported
between applications
• Some aspects belong to a different
Business Object (save bandwidth)
• References become IDs or Hyperlinks

Basic Concepts

Basic Concepts
Client

Basic Concepts
Resource
Client
Server

Basic Concepts
GET /users/Joachim
HTTP Request
Resource
Client
Server

Basic Concepts
GET /users/Joachim
HTTP Request
Resource
Client
Server
HTTP Response
HTTP/1.1 200 OK
Content-Type: application/xml
<?xml version=...>
<User firstname=“...

Basic Concepts
GET /users/Joachim
HTTP Request
Resource
Client
Server
HTTP Response
HTTP/1.1 200 OK
Content-Type: application/xml
<?xml version=...>
<User firstname=“...
Contents can be
XML, JSON, CSV, Binary Data
...any MIME-Type

HTTP and Response
Codes: GET
• 200 OK
• 400 Bad Request
• 401 Unauthorized / 403 Forbidden
• 404 Not found
• 500 Internal Server Error

HTTP Methods and
Codes: POST
• 201 Created
• 409 Conflict
• 415 Unsupported Media Type
• 500 Internal Server Error
• Many more ...

Useful Advanced
HTTP - Features
• If-Modified-Since / Last-Modified / 304 Not
Modified for caching
• Cache-Control (read-only objects or
infrequently changing objects)
• Content-Type to determine marshalers
• Accept-Ranges / Content-Range for partial
loading of long lists etc.

Benefits of bare HTTP?
• Reduced Complexity: HTTP is easy
• Advantage in Development & Maintenance
• Uniform interface (HTTP) to every
resource
• More flexibility: serving/accepting
Resources instead of exposing a set of
operations (➠Mashups)

RESTful Web Services
with VA Smalltalk

Ingredients for
RESTful Web Services
• HTTP communications (Possibly HTTPS)
• Transport format for resource data
• XML, JSON, plain ascii
• Marshalling and unmarshalling on both ends
• Naming Service (URI ➠ Resource ➠ URI)

VAST provides all the
Building Blocks
• Server Smalltalk
• HTTP Client and Server
• Highly configurable and extendable on
many levels
• Scalable (Multithreading by default)
• Mature (~10 years) and in use
• XML marshalling

Building a
REST Client
• Extends SstHttpClient
• Adds xml marshalling (or other marshalling
like)
• Wraps simple HTTP requests and handles
response codes
• Optional: Session / cookie handling,
caching ... (Maybe not „pure“ REST)

PRESTON client
• getResourceNamed: aURI
queryParameters: aDictionary
• postResource: anObject
toResourceNamed: aURI
• deleteResourceNamed: aURI
• getOptionsForResourceNamed: aURI
• handles session cookies (optional)

PRESTON client
• Mapping between Resource (e.g. XML) and
Smalltalk objects
• Optional caching (URI → object)
• Proxies for hyperlinks
(linked resource is only fetched if needed)
• Can act as database client to a RESTful web
service

Building a
REST Server
• Extends several components of SST HTTP
Server
• Is very similar to a servlet container (it
serves resources with a certain URI)
• Adds marshalling, naming and more

SST Building Blocks
SstServerApplicationContext
SstBasicServer containerKey
sessionManagerConfig.
attributes
applicationContexts
sessionManagers
initializeRequest:
handlesRequest:
startUp SstHttpSessionManager
shutDown
processClientRequest:
basicProcessRequest:
createSessionForRequest:
processRequest:
createCookieForSession:
SstHttpServer
cookieFromRequestHeader...
SstHttpServletEngine

PRESTON Server
SstServerApplicationContext
SstBasicServer containerKey
sessionManagerConfig.
attributes
applicationContexts
sessionManagers
initializeRequest:
handlesRequest:
startUp SstHttpSessionManager
shutDown
processClientRequest:
basicProcessRequest:
createSessionForRequest:
processRequest:
createCookieForSession:
SstHttpServer
cookieFromRequestHeader...
PrestonResourceManager
PrestonApplicationContext
supportedHttpMethods
resourceManagers
PrestonServer
pathSegment
xmlMappingSpec
rootObject
handleGETRequest..
handlePostRequest...

Demos
• Yahoo! Traffic Client
• Yahoo! Traffic Client on a Seaside Server
• Todomatic Server & Client

GET MapsService/V1/trafficData
with request parameters
PRESTON Client
Yahoo! Traffic REST API
http://local.yahooapis.com/
HTTP
Application Logic
Response
with XML
Sample Request URI:
http://local.yahooapis.com/MapsService/V1/trafficData?
appid=YdnDemo&street=701+First+Ave&city=Sunnyvale&state=CA
VA Smalltalk Image

ith
eventually w
ody
a message b
ML
containing X
document
GET users/joachim/todolists
POST users/joachim/todolists
HTTP Client
OODB Todomatic PUT users/joachim
* Web Browser
RESTful Server * PRESTON Smalltalk client
VA Smalltalk Image * Any other HTTP Client
TodoLists and
TodoItems nse
HTTP Respo
l
with optiona
ent
XML Docum
User TodoList TodoItem

Summary

RESTful Web Services
• Anywhere on the web today and growing
• Far less complex than Web Services
• HTTP standard all the way down
• Can be used for Internet applications as
well as for internal systems
• Integration
• Scaling

VA Smalltalk and
RESTful Web Services
• Most Web Services are CRUD operations
• Integration today mostly means combining
HTTP with XML or other text formats
• VA ST provides all the building blocks
• Some extensions needed
• Can be combined with Seaside easily
• Mashup your own services

Questions?
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Joach erwe
Flied rmany
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sbur tfabr
dwig bjek
40 Lu el@o ik.de
tfabr
716 tuch
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More info on my blog:
www.joachim-tuchel.de