Designing to an Interface

1
Designing to an Interface

• Dave Elliman

2
Is there a book?

• Gregor Hohpe and Bobby Woolf, Enterprise
  Integration Patterns, Addison-Wesley, 2004.
• A remarkable well-written and authorative text
• Martin Fowler, Patterns of Enterprise
  Application Architecture. Addison-Wesley, 2003.
• Martin Fowler is the chief Guru in this field

3
Yet Another Choice

• Synchronous or Asynchronous
• Synchronous
• more familiar
• less complex
• Have to wait for it
• Asynchronous
• more robust
• Can send and forget
• More loosely coupled

4
Some more terminology?

• MOM
• Message Oriented Middleware
• SOA
• Service Oriented Architectures

5
Design to an Interface

• Careful thought about Use Cases allows one to
  specify an Interface
• It is important to get this right as it is a
  nuisance to change later
• Once the application is deployed Interfaces are
  forever
• RPC is the easiest approach to understand but
  consider asynchronous approaches as well i.e. SOA

6
We need a case study

• A Vision for online learning as a process of
  colouring an ontology
• Could this be what education has been missing
  the killer application?
• No Ok Anyway
• We need topics and relationships
• T1subtopic T2
• T1 prerequisite T3

7
We have actors

• Student
• Tutor
• Maybe Administrator and System

8
Groups, Test and Tutorials

• Student
• Tutor
• Group
• Test
• Tutorial

9
Consider the Interface

• This is really important to get right

10
Start with user stories

• The tutor creates a group of students
  corresponding to his class for a topic
• The tutor create a topic and adds tests and
  tutorial material
• A student sees what he is able to learn next and
  studies it
• A student decides he is ready to be tested and
  selects a test on a topic
• The tutor sees the progress overall and where
  students are stuck

11
Exercise

• Draw the Use Case UML diagrams for this case
  study

12
Student Methods

• login
• logoout
• learningChoices
• getTutorial
• testMe

13
Tutor methods

• createGroup
• assignTopicToGroup
• seeStudentProgress
• seeGroupProgress
• disbandGroup
• addTutorial
• addTest
• addTopic

14
Admin Methods

• createStudent
• archiveStudent
• createGroup
• deleteGroup
• createTutor
• deleteTutor

15
Web Services

• Dave Elliman

16
What is a web service?

• Usually
• A method call that uses XML to encode the request
  and response
• This uses SOAP (XML again) or XML RPC
• A service that describes itself using a wsdl
  description (XML of course).

17
For Example

• http//www.sirajgadhia.com/WebServices/quotes.asmx
  ?wsdl
• http//ws.cdyne.com/emailverify/Emailvernotestemai
  l.asmx

18
Web Services are loosely coupled

• Web services are an inspired idea
• The key ideas are
• A web service is a remote object that you can use
  over the internet
• It communicates in XML (SOAP) and this means any
  operating system on any machine can use it
• The object is located at a URL. At that url there
  is also a standard description of what it does
  (.wsdl) (like reflection and introspection in
  classes only better)

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Interoperability

• Interoperability
• Does not matter about make of computer, operating
  system, or programming language
• Suitable for automatic tools to do all the hard
  work
• Especially useful for Business to Business
  transactions

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Why use web services?

• A general paradigm for building distributed
  applications
• Enables legacy code to be incorporated in
  state-of-the-art systems by use of a web-service
  wrapper
• Facilitates INTEGRATION between organisations
• Intranet and knowledgebase
• Supply chain
• E Government etc etc

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Web services may be foundusing directories

• Universal Description Discovery and Integration
• An indexing service for web services
• See microsoft and IBMs examples
• http//uddi.microsoft.com/default.aspx
• http//www-306.ibm.com/software/solutions/webserv
  ices/uddi/

22
A Layered model
Workflow - WSFL
Service Discovery- UDDI
Service Description - WSDL
Messaging - SOAP
Transport - HTTP (not exclusively)
Internet
23
Benefits

• There is a huge payoff in efficiency
• It was previously an expensive nightmare to
  achieve INTEROPERABILITY no longer
• Leverage of existing applications
• Accessibility to services
• The market was estimated to be worth 40 billion
  by 2008 nonsense?
• Another chance to be a millionaire?

24
The old way..

• Complicated System inter-connection
• All individually specified and engineered
• Tied into obsolete hardware and systems
• Highly paid staff needed
• Lots of info needed to pass between parties
• Difficult to change later

25
More about SOAP

• SOAP is an XML envelope
• The header is often taken from a URL
• See
• http//www.intertwingly.net/stories/2002/03/16/aGe
  ntleIntroductionToSoap.html

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An example
ltSOAPEnvelope xmlnsSOAP "http//schemas.xmlsoa
p.org/soap/envelope/"gt  ltSOAPBodygt   
ltmgetStateName xmlnsm"http//www.soapware.org/"
gt      ltstatenumgt41lt/statenumgt   
lt/mgetStateNamegt  lt/SOAPBodygtlt/SOAPEnvelopegt
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WSDL (XML)
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Almost always processed by a tool not a person

• Can see the wsdl by pointing your browser at any
  web service eg
• http//www.sirajgadhia.com/WebServices/quotes.asmx
  ?wsdl

29
SOAP must implement

• An XML envelope for XML (SOAP is transport
  independent)
• An HTTP binding for SOAP messaging
• A convention for doing RPC
• And a way to pass parameters - an XML
  serialization format for structured data

30
Sounds terrible!

• So I need to generate SOAP envelopes
• I need to send them down an HTTP Socket and
  listen for the response
• I need to parse the SOAP that is returned (SAX or
  DOM?)
• If I try RPC I need to marshal the parameters
  HELP!

31

• Thankfully not. There are TOOLS
• AXIS for the Java world (also C)
• Built into Microsoft .NET WCF
• PHP - PEAR
• Perl has SOAP libraries
• Python is of course brilliant
• many others

32
The Client Side

• When one builds a web service one can get a
  client for free offer this to people!
• We can build a client with a tool for example
  wsdl2java
• We can build a client using a library such as
  axis2.jar
• We can use Microsoft tools we will!

33
Restful Web Services

• REST we services use no soap no wsdl
• Faster and conceptually simpler and require no
  special tools
• Based on Roy Fielding's PhD thesis
• Not a standard a way of doing things
• http//www.parts-depot.com/parts
• http//www.parts-depot.com/parts/003
• POST sending xml for an order

34
Summary

• Web services are a powerful idea and they are
  becoming hugely important
• We will build a web service to expose the methods
  for the case study
• Quite easy to use in practice given current state
  of tools

35
Deploying a web service
36
How to offer a web service

• I downloaded Apache Tomcat from
• http//tomcat.apache.org/ on weed.cs.nott.ac.uk
• I installed it on port 80 (not default of 8080)
• Check at http//weed.cs.nott.ac.uk/
• I downloaded Apache Axis 2 (the web version) for
  building web services
• http//ws.apache.org/axis2
• I extracted axis2.war to
• ltsomewheregt/tomacat 6/webapps
• I stopped and re-started the tomcat server.
• http//weed.cs.nott.ac.uk/axis2

37
How to create and deploy a web service

• We are spoiled for choice of course At least
  five different ways but it is only 3 steps. use
  ant
• Compile a simple Java POJO class
• Generate the WSDL for this class
• Create an .aar file. (Just a jar really).
• Put the .aar file inlttomcatgt/webapps/axis2/WEB_INF
  /services
• It is hot deployed at once

38
We need ant
39
What is ant

• Ant is a build tool reminiscent of make but not
  so evil (eg can fail with a space in front of a
  tab!)
• It is open source
• It is powerful and extendible
• It is written in Java and is portable
• No o/s specific system calls
• An ant build file is written in xml

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Setting ant up

• You can get ant from http//ant.apache.org/
• Just extract the zip file ltsomewheregt
• Set the ltsomewheregt\ ant\bin directory in your
  PATH
• Set the ANT_HOME environment variable to
  ltsomewheregt\ant

41
Some environment variables

• ANT_HOMEC\ant
• JAVA_HOMEC\jdk1.6.05
• PATHC\ant\binC\jdk1.6.05\bin

42
Invoking ant

• Similar to running make
• ant options target target2 ...
• Options
• -help print this message
• -verbose be extra verbose
• -debug print debugging
  information
• -buildfile ltfilegt use given buildfile
• ant (assumes build.xml in .)

43
Things to know

• Written in XML
• You can call ant recursively used a lot!
• build.xml is the default name
• No Java programmer can live without ant
• http//ant.apache.org .

44
Simple ant script

ltproject name"hello" default"compile"gt lttarget
name"compile"gt ltjavac srcdir"." destdir"."
/gt lt/targetgt lt/projectgt
45
The Build File Will Create a dependancy Tree

• You specify targets
• Each is executed only once honouring the order of
  dependency
• If files are up-to-date the task is not executed
• eg the test and deploy targets would depend on
  the compile target

46
How Is This dependancy Expressed?

• lttarget nameall dependstest, javadoc,
  deploy
• descriptionrun tests, document and deploy
• /gt

47
This is easier than make
lttarget namecompile dependsprepare descripti
oncompile the sources ltjavac
srcdirscrDir destdirbuildDir/gtlt/targe
tgt Earlier in the file we define
properties ltproperty namebuildDir
valueclasses/gt
48
see http//ant.apache.org/manual/CoreTasks/
Standard Targets

• prepare
• clean
• compile
• Javadoc
• test

49
For the case study

• ltproject name"CM6" basedir"."
  default"generate.service"gt
• ltproperty name"AXIS2_HOME" value"C/axis2/axis
  2-1.3"/gt
• ltproperty name"build.dir" value"build"/gt
• ltpath id"axis2.classpath"gt
• ltfileset dir"AXIS2_HOME/lib"gt
• ltinclude name".jar"/gt
• lt/filesetgt
• lt/pathgt

50
Compile task
lttarget name"compile.service"gt ltmkdir
dir"build.dir"/gt ltmkdir
dir"build.dir/classes"/gt lt!--First
let's compile the classes--gt ltjavac
debug"on" fork"true"
destdir"build.dir/classes"
srcdir"basedir/src"
classpathref"axis2.classpath"gt lt/javacgt
lt/targetgt
51
Create WSDL Task
lttarget name"generate.wsdl" depends"compile.serv
ice"gt lttaskdef name"java2wsdl"
classname"org.apache.ws.java2wsdl.Java2WSD
LTask" classpathref"axis2.classp
ath"/gt ltjava2wsdl className"com.dge.Cours
eMarker6.0" outputLocation"b
uild.dir" targetNamespace"htt
p//CM6/"gt ltclasspathgt
ltpathelement path"axis2.classpath"/gt
ltpathelement location"build.dir/classe
s"/gt lt/classpathgt
lt/java2wsdlgt lt/targetgt
52
Create aar file
lttarget name"generate.service"
depends"compile.service"gt lt!--aar them
up --gt ltcopy toDir"build.dir/classes"
failonerror"false"gt ltfileset
dir"basedir/resources"gt
ltinclude name"/.xml"/gt
lt/filesetgt lt/copygt ltjar
destfile"build.dir/StockQuoteService.aar"gt
ltfileset excludes"/Test.class"
dir"build.dir/classes"/gt lt/jargt
lt/targetgt lt/projectgt
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Once you get build.xml right its easy

• We create an Interface
• We create a POJO that implements this
• We create a build.xml to make an aar file
• We run ant
• We have a web service
• (Some auto-deploy options seem easier but only
  for the very simplest cases)
• Annotation-based methods are a competitor to this
  _at_WebService _at_Webmethod etc
• Used to involve a lot of xml several special Java
  classes and deploytool.. was much harder!

54
Wow.. That was a lot to take in

• Any Questions?