Web Services - A brief overview

Web Services - A brief overview

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  Introductio n to Web Services
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  Web Services • AWeb 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.
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  Why web services? •Your application can publish its function or message to the rest of the world.
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  WEB Services REST Services SOAP and WSDL Department of Information Science Engg
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  REST Services • Relyingon URIs and HTTP verbs • Usage of 5 big HTTP verbs POST, HEAD, GET, PUT, DELETE Nothing more than CRUD concept of the Web • Ex: Delicious APIs Delicious is a leading social bookmarking service Visit: http://www.peej.co.uk/articles/restfully-delicious.html • Data exchange format XML, JASON or both
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  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
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  • A serviceis 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.
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  A SOAP messageis 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.
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  A SOAP request: <?xmlversion="1.0"?> <soap:Envelope xmlns: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>
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  The SOAP response: <?xmlversion="1.0"?> <soap:Envelope xmlns: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>
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  WSDL • WSDL standsfor 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 called o What parameter it expects o What data structure it returns o Which port the application uses o Which protocol the web service uses (like https)
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  Need for stubs(similar to RMI)
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  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.
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  Comparision REST services SOAP services • Architectural style • XML-based protocol • Simply calls services via URL • Invokes services by calling path RPC method • Lightweight – not a lot of • Rigid – type checking, extra xml markup adheres to a contract • Easy to build – no toolkits • Development tools – WSDL required Soap analyser tool, oXygen XML