WebServices Basic Overview
- 2. 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.
- 3. Why web services? • Your application can publish its function or message to the rest of the world.
- 4. Department of Information Science Engg WEB Services REST Services SOAP and WSDL
- 5. REST Services • Relying on 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
- 6. 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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- 8. • 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.
- 9. 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.
- 13. 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 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)
- 14. Need for stubs (similar to RMI)
- 15. 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.
- 17. 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