Introduction to Web Services

Transcription

1 Introduction to Web Services Asst. Prof. Chaiporn Jaikaeo, Ph.D. Computer Engineering Department Kasetsart University, Bangkok, Thailand

2 Traditional World-Wide-Web Designed for human-to-app interactions Information sharing (Non-automated) E-commerce Built on top of HTTP for data transfer HTML for representing document 2

3 What's Next? Try taking humans out of the loop Systematic application-to-application interaction over the web Automated e-commerce Resource sharing Distributed computing Web services (another) effort to build distributed computing platform for the web 3

4 Web Services vs. Web Apps Web application Provides service directly to user browser web server HTTP Web service or (Web API) Provides service to other programs app (service user) HTTP web server (service provider) 4

5 Web Service Protocols Simple Object Access Protocol (SOAP) Service requests and responses are always done via XML messages, called SOAP envelope Formally supported by World Wide Web Consortium (W3C) Representational State Transfer (REST) Service requests are done via generic HTTP commands: GET, POST, PUT, DELETE Simpler set of operations 5

6 Other Web Service Protocols Web feeds RSS Atom Remote procedure call JSON-RPC XML-RPC JavaScript 6

7 Sample SOAP Message E.g., message requesting IBM stock price POST /InStock HTTP/1.1 Host: Content-Type: application/soap+xml; charset=utf-8 Content-Length: 299 HTTP Header <?xml version="1.0"?> <soap:envelope xmlns:soap=" <soap:header> </soap:header> <soap:body> <m:getstockprice xmlns:m=" <m:stockname>ibm</m:stockname> </m:getstockprice> </soap:body> </soap:envelope> SOAP Envelope Desired operation (Verb) Object of interest (Noun) 7

8 Sample REST Request E.g., message requesting IBM stock price GET /stock/ibm HTTP/1.1 Host: Desired operation (Verb) Object of interest (Noun) HTTP Header The above corresponds to the URL 8

9 Data Interchange Formats XML extensible Markup Language E.g., RSS, Atom <?xml version="1.0" encoding="iso "?> <rdf:rdf xmlns:rdf=" xmlns=" <title>slashdot</title> <link> <description>news for nerds, stuff that matters</description> <dc:subject>technology</dc:subject> <items> <rdf:seq> <rdf:li rdf:resource=" Laptops-Shipped-CPU-Choking-Wi-Fi-Driver?from=rss" /> </ref:seq> </items> </rdf:rdf> Large collection of libraries for processing XML 9

10 Data Interchange Formats JSON JavaScript Object Notation Can be directly evaluated in JavaScript Typically smaller than XML Libraries for other languages are also available { } "Person": { "firstname": "John", "lastname": "Smith", "age": 25, "Address": { "streetaddress":"21 2nd Street", "city":"new York", "state":"ny", "postalcode":"10021" }, "PhoneNumbers": { "home":" ", "fax":" " } } JSON <Person> <firstname>john</firstname> <lastname>smith</lastname> <age>25</age> <Address> <streetaddress>21 2nd Street</streetAddress> <city>new York</city> <state>ny</state> <postalcode>10021</postalcode> </Address> <PhoneNumbers> <home> </home> <fax> </fax> </PhoneNumbers> </Person> XML 10

11 Example Wikipedia RESTful API reference Example uery&titles=kasetsart%20university&prop=revisions&rvp rop=content 11

12 Example HostIP.info RESTful Determines geographical location of the specified IP address API documentation Example 12

13 Coding Example E.g., accessing HostIP.info from Python import sys import json from urllib import urlencode from urllib2 import urlopen response = urlopen(' + urlencode({ 'ip' : sys.argv[1], })) data = json.loads(response.read()) print 'IP Address: %s' % data['ip'] print 'City: %s' % data['city'] print 'Country: %s' % data['country_name'] 13

14 Mashups A mashup is a webpage or application that offers new services by combining data or functionality from two or more sources Main characteristics of mashups Combination Visualization Aggregation They aim to make existing data more useful Example: Wikipediavision Google Maps + Wikipedia 14

15 More Resources Search engine for web APIs and mashups 15