Introduction to

Web Services

-B R RaveendraPESIT,Bangalore

Web Services

• A Web service is a method of communication between two electronic devices over the World Wide Web

• In other words, a web service helps to convert your application into a web-based application.

Why web services?

• Your application can publish its function or message to the rest of the world.

Department of Information Science Engg

WEB Services

REST Services SOAP and WSDL

REST Services

• Relying on URIs and HTTP verbs• Usage of 5 big HTTP verbs

POST, HEAD, GET, PUT, DELETENothing more than CRUD concept of the Web

• Ex: Delicious APIsDelicious is a leading social bookmarking serviceVisit: http://www.peej.co.uk/articles/restfully-delicious.html

• Data exchange formatXML, JASON or both

SOAP based services

• Simple Object Access Protocol• Exclusively use XML as the data format to exchange info

over HTTP.• A service that needs to be used by another service needs

to specify its usage through a “Service Description”. • In this case, we use WSDL – Web Services Description

Language• Ex: Apache Axis, Apache CXF• SOAP has nothing to do with SOA – Service Oriented

Architecture

continued…...

Continued……. • A service is hosted on a “Discovery Service” in the internet.

• A client which wants to use this service will have to “discover”

this service (similar to RMI) using the ‘Discovery Service’.

• Once the service is “discovered”, the client asks the service

how it should be invoked. The service replies in WSDL format.

• The service is now invoked using SOAP. The client issues a ‘SOAP Request’.

• The service responds with a ‘SOAP Response’, which includes the result.

A SOAP message is an ordinary XML document

containing the following elements:• Envelope - identifies the XML document as a SOAP message

o Header - contains information about the request.

o Body

Message data - contains request and response information

itself.

Fault (optional) - containing errors and status information.

<?xml version="1.0"?><soap:Envelopexmlns:soap="http://www.w3.org/2001/12/soap-envelope"soap:encodingStyle="http://www.w3.org/2001/12/soap-encoding">

<soap:Body xmlns:m="http://www.example.org/stock">  <m:GetStockPrice>    <m:StockName>IBM</m:StockName>  </m:GetStockPrice></soap:Body>

</soap:Envelope>

A SOAP request:

<?xml version="1.0"?><soap:Envelopexmlns:soap="http://www.w3.org/2001/12/soap-envelope"soap:encodingStyle="http://www.w3.org/2001/12/soap-encoding">

<soap:Body xmlns:m="http://www.example.org/stock">  <m:GetStockPriceResponse>    <m:Price>34.5</m:Price>  </m:GetStockPriceResponse></soap:Body>

</soap:Envelope>

The SOAP response:

Continued……

WSDL

• WSDL stands for Web Services Description Language• It is an XML-based language that is used for

describing the functionality offered by a Web service.• WSDL file contains info about

o How the service can be calledo What parameter it expectso What data structure it returnso Which port the application useso Which protocol the web service uses (like https)

Need for stubs (similar to RMI)

What are stubs?

• A stub is a small program routine that substitutes for a longer program, possibly to be loaded later or that is located remotely.

• The stub accepts the request and then forwards it (through another program) to the remote procedure.

• When that procedure has completed its service, it returns the results or other status to the stub which passes it back to the program that made the request.

Comparision

REST services• Architectural style• Simply calls services via URL

path• Lightweight – not a lot of

extra xml markup• Easy to build – no toolkits

required

SOAP services• XML-based protocol• Invokes services by calling

RPC method• Rigid – type checking,

adheres to a contract• Development tools – WSDL

Soap analyser tool, oXygen XML

THANK YOU