1. General introduction to Web services and an implementation example
EuroFIR Web Services
General introduction to Web services and an implementation example
Karl Presser

2. Agenda History and background of Web services WS Components SOAP WSDL
UDDI
REST and Mashups
An example using Apache AXIS

3. History and Background
The original purpose of HTTP was to provide a way to publish and retrieve hypertext pages over the internet
Browser
Web Server
CGI
Middleware
Application server
user program DB

4. History and Background
Business to Business
Security
Internet
Firewall
Firewall
Only port 80
Only port 80
Web Server
Middleware
Application server DB
CGI
User program
Web Server
Middleware
Application server DB
CGI
User program
Remote Procedure Call (RPC),
CORBA or DCOM
Already implemented
Already implemented
Not local
Client stub
Server stub
directory

5. History and Background
The idea of Web Services
use existing software systems
use port 80/25 to get through all firewalls
use a standard representation schema, e.g. xml
make it platform independent
make it programming language neutral
construct it modularly for reuse
make it secure, reliable, transactional and …
Client
Stub
Wrapping system
internet
Wrapping system
Stub
Server

6. WS Components
Service registry
SOAP (simple object access protocol) as transport protocol
WSDL (web service description language)
UDDI (universal description and discovery protocol)
find
publish
Service description
Service requester
Service provider
bind
Service description
Service interface
Service

7. SOAP SOAP as RPC mechanism Client call Stub, runtime service location
SOAP system
HTTP support (web client)
INTERNET
Wrap doc in HTTP Post request
Serialized XML Doc
Server
do()
Stub, runtime adapters
SOAP system
HTTP support (web client)
Wrap doc in HTTP Post request
Serialized XML Doc

8. SOAP
SOAP is …
Envelope
a message construct: A message format for communication using XML
a processing model: Rules for SOAP message
a extensibility model: How to extend basic massages with specific information
a protocol binding framework: Allow different protocols like HTTP or SMTP
a convention on how to turn a RPC all into a SOAP message und vise versa
Language independent
Header
Header block
Header Block
Body
Body element

9. WSDL Describes the interface of a Web service using XML schema
<element name =“food” type = tns:foodType”/>
<complexType name=“foodType”>
<all>
<element name=“id” type=“int”/>
<element name=“name” type=string”/> …
</complexType>
<operation name="GetFood" pattern=“…"> <input messageLabel="GetMsg" element="tns:request"/>
<output messageLabel="SuccessfulMsg" element="tns:food"/> </operation>
<binding name="RESTfulInterfaceHttpBinding" interface="tns:RESTfulInterface" type=" …/>
>endpoint adress= “…”…/>
Describes the interface of a Web service using XML schema
The types used in the service model
The messages for communication
The operations
The mapping to transport protocols
The location of the service provider

10. UDDI
Originally, UDDI was build as an “Universal Business Registry” similar to a search engine like Google.
It contains
business information like the name of the company
business service offered by the company
bindingTemplate which are technical information of the service
tModel which can be used for additional information e.g. conditions for using the Web service

11. WS Standards and Spec

12. REST and Mashups
REST is a collection of network architecture principles. It is used to describe interfaces which transmit domain-specific data over HTTP without further detail about the messaging layer
Application state and functionality are provided using resources
Every resource is uniquely addressable
REST is stateless -> no need to store information
For processes where a lot of context information is needed, the REST-url is getting longer and longer
Procedures:
getUser()
addUser()
removeUser()
updateUser()
REST examples:
userResource = new Resource('
userResource.delete()

13. REST and Mashups
A Mashups is web application that combines data from more than one source into a new web service.
An example is the Chicago Police Department which has a Mashup that integrates their department’s database of reported crimes with Google Maps.

14. Apache Axis
Apache Axis is an implementation of the SOAP submission to W3C. It is a Java library that helps you to implement all tasks around SOAP and the installation on Apache AXIS is quite simple.
The following example shows simplified the steps that are needed:
1. Take a java class (food_apple) and write your methods:
public String food() { 
String s = “apple”;
return s; }
public long time() { 
return System.currentTimeMillis();

15. Apache Axis 2. Generate the WSDL file using Java2WSDL :
javac food_apple
java org.apache.axis.wsdl.Java2WSDL –o food_apple.wsdl … food_apple
3. Generate the stub files using WSDL2Java:
java org.apache.axis.wsdl.WSDL2Java … food_apple.wsdl
As a result you find food_appleService.java, food_appleSoapBindingSkeleton.java, food_appleBindingImpl.java, food_apple.wsdd and food_apple.java
which are used on the server side.
food_appleServiceLocator.java, food_appleSoapBindingStub.java and food_apple.java
which are used on the client side.

16. Apache Axis
4. Copy your method from step 1 into the file food_appleSoapBindingImpl.java
5. Compile all files
javac *.java
6. Deploy the web service using AXIS AdminClient
java org.apache.axis.client.AdminClient … deploy.wsdd
7. Write the client using
food_appleServiceLocator l= new food_appleServiceLocator();
food_appleSoapBindingStub stub = l.getfood_apple():
System.out.println(stub.food());
System.out.println(stub.time());

17. Thanks for your attention