EuroFIR Web Services

General introduction to Web services and an implementation

example

Karl Presser

Agenda

1. History and background of Web services

2. WS Components

• SOAP

• WSDL

• UDDI

3. REST and Mashups

4. An example using Apache AXIS

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

Middleware

Application server

DB

user program

History and BackgroundBusiness to Business

Web Server

Middleware

Application server

DB

User program

Web Server

Middleware

Application server

DB

User program

Internet

Firewall Firewall

Remote Procedure Call (RPC),CORBA or DCOM

Client stub

Server stub

directory

Not local

Already implemented

Only port 80 Only port 80

Already implemented

Security

History and BackgroundThe 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

Server

Stub

Stub

Wrapping system

Wrapping system

internet

Service requester

WS Components

• SOAP (simple object access protocol) as transport protocol

• WSDL (web service description language)

• UDDI (universal description and discovery protocol)

Service registry

Service provider

bind

find publish

Service description

Service interface

Service

Service description

SOAP

Client

call

Stub, runtime service location

SOAP system

Serialized XML Doc

Wrap doc in HTTP Post request

HTTP support (web client)

SOAP as RPC mechanism

Server

do()

Stub, runtime adapters

SOAP system

Serialized XML Doc

Wrap doc in HTTP Post request

HTTP support (web client)

SOAPSOAP is …

• 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

Envelope

Header

Body

Header block

Header Block

Body element

WSDL

• 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

<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="http://www.w3.org/ns/wsdl/http"> …/>

>endpoint adress= “…”…/>

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

WS Standards and Spec

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:

http://example.com/users/

http://example.com/users/karl

userResource = new Resource('http://example.com/users/karl')

userResource.delete()

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.

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();

}

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.

Apache Axis

4. Copy your method from step 1 into the file food_appleSoapBindingImpl.java

5. Compile all filesjavac *.java

6. Deploy the web service using AXIS AdminClientjava org.apache.axis.client.AdminClient … deploy.wsdd

7. Write the client usingfood_appleServiceLocator l= new food_appleServiceLocator();food_appleSoapBindingStub stub = l.getfood_apple():

System.out.println(stub.food());System.out.println(stub.time());

Thanks for your attention