1. RESTful Web Services

2. Web Services Classification
“Big Web Services”
Traditional enterprise Web services
SOAP & WSDL
“Lighter-weight Web Services”
RESTful approach
Web API (feature of Web 2.0)
Mashups

3. RESTful REST (REpresentational State Transfer)
is an architectural style for accessing information on the Web
The term REST was introduced
and defined in 2000 by
Roy Fielding in his
doctoral dissertation

4. Another definition Definition from:
REST is a key design idiom that embraces a stateless client-server architecture in which the web services are viewed as resources and can be identified by their URLs

5. Key REST principles
REST is a set of principles that define how Web standards, such as HTTP and URIs, are supposed to be used
Give every “thing” an ID
Link things together
Use standard methods (GET, POST,…)
Resources with multiple representations
Communicate statelessly

6. [1] Give every “thing” an ID
On the Web, there is a unified concept for IDs:
The URI
URIs make up a global namespace, and using URIs to identify your key resources means they get a unique, global ID

7. [1] Give every “thing” an ID
Use URIs to identify everything that merits being identifiable
All of the “high-level” resources that your application provides, whether they represent
individual items
collections of items
virtual and physical objects
computation results

8. Set of URIs for bookmarking system
List all users
Provides specific user details
List all user bookmarks
Provides specific user bookmark details

9. [2] Link things together
Sample Web service response:
Links are provided, so an application that has retrieved this document can “follow” the links to retrieve more information
<order self=' > <amount>23</amount> <product ref=' /> <customer ref=' /> </order>

10. [3] Use standard methods
RESTful web services use HTTP protocol methods for the operations they perform
Source:

11. [4] Multiple representations
Client and Web service may exchange data in a variety of formats, e.g.
XML
JSON
YAML
To understand each other a content negotiation procedure may be applied
Web service may provide multiple representations of
resources
A client may ask for a representation in a particular format

12. Content negotiation Client set an ‘Accept’ header: URI-based:
GET /foo
Accept: application/json
GET /customers/1234 HTTP/1.1 Host: example.com Accept: text/x-vcard
GET /customers/1234 HTTP/1.1 Host: example.com Accept: application/vnd.mycompany.customer+xml
GET /foo.json

13. HTTP Request/Response as REST
Source:

14. JSON
JSON (JavaScript Object Notation) is a lightweight computer data interchange format
Text-based, human-readable format for representing simple data structures and associative arrays
easy for humans to read and write
easy for machines to parse and generate
Is based on a subset of the JavaScript programming language
MIME type: application/json

15. JSON example JSON Web page: http://json.org/ { "firstName": "John",
"lastName": "Smith",
"address": {
"streetAddress": "21 2nd Street",
"city": "New York",
"state": "NY",
"postalCode": 10021 },
"phoneNumbers": [
{ "type": "home", "number": " " },
{ "type": "fax", "number": " " } ],
"newSubscription": false,
"companyName": null }
JSON Web page:

16. YAML
YAML is yet another human-readable data serialization format (first proposed in 2001)
Takes concepts from programming languages such as C, Perl, and Python, and ideas from XML
YAML is a recursive acronym for
"YAML Ain't Markup Language“
(data-oriented, rather than document markup)
Early in its development:
"Yet Another Markup Language"

17. YAML example --- receipt: Oz-Ware Purchase Invoice date: 2007-08-06
customer:
given: Dorothy
family: Gale
items:
- part_no: A4786
descrip: Water Bucket (Filled)
price:
quantity: 4
- part_no: E1628
descrip: High Heeled "Ruby" Slippers
price:
quantity: 1
...

18. JSON versus YAML JSON syntax is a subset of YAML 1.2
Most JSON documents can be parsed by a YAML parser
JSON's semantic structure is equivalent to the optional "inline-style" of writing YAML
The Official YAML Web Site:

19. What Makes Up a RESTful Service?
The definition of RESTful web service consists of
The base URI for the web service
e.g.
The MIME type of the data supported by the web service
e.g. JSON, XML, YAML
The set of operations supported by the web service using HTTP methods
e.g. POST, GET, PUT, DELETE

20. JAX-WS for RESTful Web Services
The Java API for XML Web Services (JAX-WS) provides full support for building and deploying RESTful Web services
Sun article about programming RESTful Web Services with JAX-WS:
But there is another specification JAX-RS
Java API for RESTful Web Services

21. JAX-RS JSR 311: http://jcp.org/en/jsr/detail?id=311
Part of the Java EE 6 platform, JAX-RS fully supports REST principles
Uses annotations to simplify the development of RESTful web services
Allow you to expose simple POJOs as web resources

22. Jersey Sun offers the open source, production quality
Reference Implementation for JAX-RS
code-named Jersey
Jersey also provides an API so that developers may extend Jersey to suite their needs

23. The Resource Class
JAX-RS resource is any POJO that is annotated with relative URI path as value
The base URI is the application context
import javax.ws.rs.Path;
@Path("/stockquote")
public class StockResource {
......
public String getStockInfo() {
return "This is Stock Information"; }

24. Resource Methods
Resource methods are public methods of a resource class that you identify with a request method designator
The return values of methods with request designator annotations are generally
void
a Java language type
javax.ws.rs.core.Response

25. Example ( http://www.javapassion.com/webservices/jaxrs.pdf )
// Assume the application context is
// then //
// GET
// - handled by the getList method
// GET
// - handled by the getWidget method.
@Path("widgets")
public class WidgetsResource {
@GET
String getList() {...}
String String id) {...}

26. URI Path Template
URI path templates are URIs with variables embedded within the URI syntax
The value of the bookmark variable may be obtained by adding on method parameter
// Will respond to
@Path("/bookmarks/{bookmark}")
public class BookmarkResource {
@GET
public String getBookmark(
@PathParam("bookmark") String bookmarkId) {
... }

27. Resource method parameters
Resource methods can be annotated with one of the following annotations:

28. Sub Resources
Apart from the resource class, it is possible also to annotate methods of a resource class with annotation (sub resource methods)
@Path("/sayHello")
public class SayHello {
public SayHello() { }
@GET
@Path("lastname")
public String hello() {
GET request from the URI /sayHello/lastname
will be handled by the
hello() sub-resource method in the SayHello resource class

29. MIME Types Specification
A resource class can produce or consume any type of MIME
to specify the MIME type for the response
a representation that can be produced by a resource and sent back to the client
to specify the MIME type for the request
a representation of the specific content types that a resource can accept from an HTTP request entity

30. Example: MIME specification
public class SayHelloResource public String getXml() public String public void putXml(String content) {...} }

31. WADL
The Web Application Description Language (WADL) is an XML-based file format that provides a machine-readable description of RESTful Web services
REST equivalent of WSDL version 1.1
WSDL 2.0 can be used to describe REST Web services, thus competing with WADL

32. WADL sample
<?xml version="1.0" encoding="UTF-8" standalone="yes"?> <application xmlns=" <doc xmlns:jersey=" jersey:generatedBy= "Jersey: 0.10-ea-SNAPSHOT 08/27/ :24 PM"/> <resources base=" <resource path="/helloworld"> <method name="GET" id="getClichedMessage"> <response> <representation mediaType="text/plain"/> </response> </method> </resource> </resources> </application>

33. WADL generation Jersey generates basic WADL at runtime out of the box
Additionally, you can configure Jersey to create an extended WADL to add more information to the generated WADL
Additionally, there's the maven-wadl-plugin that allows you to create the WADL without running your REST application

34. Deployment as Web application
JAX-RS applications are packaged in WAR file and deployed on a container that supports Servlets
For JAX-RS aware containers (e.g. Jersey uses a HTTP web server called Grizzly)
web.xml can point to Application subclass
For non-JAX-RS aware containers
web.xml points to the servlet implementation of JAX-RS runtime

35. Jersey Web app configuration
<?xml version="1.0" encoding="UTF-8"?> <web-app ...> <servlet> <servlet-name>Jersey Web Application</servlet-name> <servlet-class>com.sun.jersey.spi.container.servlet.ServletContainer</servlet-class> <init-param> <param-name>com.sun.jersey.config.property.packages</param-name> <param-value>com.sun.jersey.samples.helloworld.resources</param-value> </init-param> <load-on-startup>1</load-on-startup> </servlet> <servlet-mapping> <url-pattern>/*</url-pattern> </servlet-mapping> </web-app>

36. JavaSE 6 Deployment
Use RuntimeDelegate to create instance of RESTful Web service end point
Jersey supports Grizzly, light-weight HTTP server and JAX-WS provider
Application app = new MyRESTApplication();
RuntimeDelegate rd = RuntimeDelegate.getInstance();
Adapter a = rd.createEndpoint(app, Adapter.class);
SelectorThread st = GrizzlyServerFactory.create(
“ a);

37. Jersey Sample Projects
Jersey provides a package with ~ sample projects
Description:
Download:
To run some sample projects Glassfish application server is necessary

38. Poster: Firefox Add-on
A developer tool for
interacting with web services and other web resources
that lets you
make HTTP requests,
set the entity body, and content type.
This allows you to interact with web services and inspect the results...

39. Poster: Firefox Add-on

40. Web API
Web APIs are functionalities made available by websites to their users or visitors in a programmatically way
Developers can use these Web APIs and enrich their applications with useful functions from third parties
Web API is a new direction to follow by W3C in a new working group: Web APIs Working Group

41. Web API Some of the most well-known web APIs are Some links:
Google Maps or Google Search
Yahoo Maps or Yahoo Search
eBay API
Amazon API
Paypal API
Skype API
and many more
Some links:

42. Public REST APIs arXiv API - Academic research repository

43. Mashups
Mashup is a web page or application that combines data or functionality from two or more external sources to create a new service
Easy, fast integration, frequently using open APIs and data sources
Types of mashups:
consumer mashups
data mashups
enterprise mashup

44. References
Web Services Programming (with Passion!) Hands-on Online Course
Article: A Brief Introduction to REST
Article: JAX-RS: Developing RESTful Web Services in Java

45. References JAX-RS specification JAX-RS Jersey Common REST Mistakes
JAX-RS Jersey
Common REST Mistakes

46. References Services Mashups: The New Generation of Web Applications