Introduction to RESTful Webservices in JAVA

What is REST ?
• REpresentational State Transfer
• Its an architectural style
• Its Peculiar features are
1. Client-server
2. Stateless
3. Cached
4. Uniform interface
5. Layered system
P.S.R Patnaik (CyberJungle.Org)

Components of REST Style
Architecture
• Resources are identified by uniform resource
identifiers (URIs)
• Resources are manipulated through their
representations
• Messages are self-descriptive and stateless
• Multiple representations are accepted or sent

Representation in REST
• Resources are first-class objects
– Indeed, “object” is a subtype of “resource”
• Resources are retrieved not as character
strings or BLOBs but as complete
representations

State
• “State” in REST means application/session
state
• State is associated with the content
transferred from client to server back to client
• Thus any server/application can continue
transaction from the point where it was left
off

REST
• State in REST is transferred by exchanging
messages between Server and Client
• REST messages are usually a XML or JSON
string containing information pertaining to
state of application.
• REST uses HTTP for STATE transfer and HTTP is
the most RESTful protocol with GET , PUT ,
POST , DELETE operations !!

RESTful Web Services
• Now we know what is REST and its
components , so what is RESTful webservice ?

RESTful Webservice
• A RESTful Web service follows four basic
design principles:
• Uses HTTP methods
• Be stateless as far as possible.
• Expose directory/folder structure-like URI/URL
• Transfer XML, JavaScript Object Notation
(JSON), or both.

HTTP Methods and REST
• GET: Reading access of the resource
(idempotent).
• PUT : Creates a new resource. (idempotent)
• DELETE: Removes the resources. (idempotent)
• POST: Updates an existing resource or creates
a new resource. (idempotent)

RESTful Webservice Using JAVA
• JSR 311: JAX-RS: The JavaTM API for RESTful
Web Services
• JSR 311 : API for providing support for
RESTful(Representational State Transfer) Web
Services in the Java Platform.

How to develop RESTful Webservice in
Java
• By using simple Java Servlet and conforming
to REST standards and best practices
• By using JSR 311 implementation like famous
Jersey framework , Jackson (fasterxml),
Resteasy, Apache CXF.

RESTful Webservice Best Practices
• Provide a distinct URI for each resource you
wish to expose.
• Use nouns in your URIs, they highlight the fact
that resources are things and not actions.
• Methods that map to GET should not change
any data.
• Methods that map to POST should change the
data.
• Make your service stateless.

Designing RESTful Webservice
• Define the resources the service will expose. A
service exposes one or more resources that are
organized as a tree.
• Define what actions you want to be able to
perform on each resource.
• Map the actions to the appropriate HTTP verbs.
• For example you want to create service to book
ticket. For example, booking ticket
/bookingticket/getavailability
/bookingticket/bookticket
/bookingticket/updateavailability

Simple RESTful Java Webservice
using Jersey and Eclipse Kepler
Prerequisites
• Eclipse Kepler
• Jersey API (https://jersey.java.net/)
• Apache Tomcat v7

Simple RESTful Java Webservice
• Create a Dynamic Web Project
• Configure it to use Apache Tomcat v7 as
Runtime. (ensure that tomcat runs on JDK 7)
• Add Jersey libraries to Project’s Build Path and
also lib directory of Web project
• Add a package with name “cyberjungle” to the
web project’s src directory.
• Add a java file and name it as
HelloSimpleRestfulWS.java

Simple RESTful Java Web service
• Add following code to the file
HelloSimpleRestfulWS.java
package cyberjungle;
import javax.ws.rs.GET;
import javax.ws.rs.Path;
import javax.ws.rs.PathParam;
import javax.ws.rs.core.Response;
@Path("/hello")
public class HelloSimpleRestfulWS {
@GET
@Path("/{param}")
public Response getMsg(@PathParam("param") String msg) {
String output = "Hello !! How are you " + msg.toUpperCase();
return Response.status(200).entity(output).build();
}
}

• Addweb.xml to the projects WEB-INF
<web-app id="WebApp_ID" version="2.4"
xmlns="http://java.sun.com/xml/ns/j2ee" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
xsi:schemaLocation="http://java.sun.com/xml/ns/j2ee
http://java.sun.com/xml/ns/j2ee/web-app_2_4.xsd">
<display-name>Simple Restful Web Application Using Jersey</display-name>
<servlet>
<servlet-name>jersey-serlvet</servlet-name>
<servlet-class>org.glassfish.jersey.servlet.ServletContainer</servlet-class>
<init-param>
<param-name>jersey.config.server.provider.packages</param-name>
<param-value>cyberjungle</param-value>
</init-param>
<load-on-startup>1</load-on-startup>
</servlet>
<servlet-mapping>
<servlet-name>jersey-serlvet</servlet-name>
<url-pattern>/restfulws/*</url-pattern>
</servlet-mapping>
</web-app>

• Run the application
• Browse the following URL
http://localhost:8080/SimpleRESTfulJavaWebS
ervice/restfulws/hello/psrpatnaik
• The output would look like.
Hello !! How are you PSRPATNAIK

Reference Resources
• IBM Developers Work.
• Oracle RESTfulWeb Services Developer's Guide
• Jersey User Guide.

Introduction to RESTful Webservices in JAVA

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