RESTful Services - e-Lite: Intelligent and Interactive...

RESTful Services

Sistemi Informativi Aziendali – A.A. 2012/2013

Summary

A.A. 2012/2013

Foundations

REST in Java

Sistemi Informativi Aziendali

Foundations

REST

A.A. 2012/2013

Representational State Transfer

Firstly defined by Roy Fielding (2000)

“Architectural Styles and the Design of Network-based

Software Architectures”

Has mostly displaced Web Services

Simpler

Standard

E.g. Will be part of the Java distribution through JSR-311


Basic Principles

A.A. 2012/2013

Addressability

Use HTTP methods explicitly

GET,

PUT,

POST,

DELETE

Stateless

Atomic requests (no state preservation between different requests)

Expose directory structure-like URIs

Resources identified by URIs

Transfer XML, JavaScript Object Notation (JSON) or both


Resource

A.A. 2012/2013

Resource

Thing exposed by the system to the outside world

Everything is a resource

http://elite.polito.it/people/bonino

http://elite.polito.it/people/corno

Independent from its representation

http://elite.polito.it/people/bonino bonino.html

http://elite.polito.it/people/bonino bonino.jpg




Operations on Resources

A.A. 2012/2013

GET

Defines a reading access of the resource without side-effects. The

resource is never changed via a GET request (idempotent*).

PUT

Updates/changes an existing resource (idempotent*)

DELETE

Removes the resources (idempotent*).

POST

Creates a new resource, must also be idempotent*.

* Idempotent operations can get repeated without leading to different

results.


Examples

A.A. 2012/2013

Accessing a resource (read)

GET /users/Robert HTTP/1.1

Creating a resource

POST /users HTTP/1.1

Host: myserver

Content-Type: application/xml

<?xml version="1.0"?>

<user>

<name>Robert</name>

</user>


Examples

A.A. 2012/2013

Changing a resource

To change the resource Robert

Provide a new representation for Robert in the body of a PUT

request

The old representation will not be accessible anymore

PUT /users/Robert HTTP/1.1

Host: myserver

Content-Type: application/xml

<?xml version="1.0"?>

<user>

<name>Bob</name>

</user>


Examples

A.A. 2012/2013

Delete a resource

DELETE /users/Robert HTTP/1.1


REST in J2EE

REST in J2EE

A.A. 2012/2013

JSR-311

Aka JAX-RS

Reference implementation

Jersey

Client

Server

Restful resources identified through annotations

http://jersey.java.net/


Jersey Annotations

A.A. 2012/2013 Sistemi Informativi Aziendali

Jersey + Eclipse – REST server



A.A. 2012/2013

@PATH("/HelloREST")

public class HelloREST

{

// This method is called if TEXT_PLAIN is request

@GET

@Produces(MediaType.TEXT_PLAIN)

public String sayPlainTextHello() {

return "Hello Jersey";

}

// This method is called if XML is request

@GET

@Produces(MediaType.TEXT_XML)

public String sayXMLHello() {

return "<?xml version=\"1.0\"?>" + "<hello> Hello Jersey" + "</hello>";

}

}



A.A. 2012/2013

<?xml version="1.0" encoding="UTF-8"?>

<web-app xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xmlns="http://java.sun.com/xml/ns/javaee"

<display-name>it.polito.sistinfo.services.rest</display-name>

<servlet>

<servlet-name>Jersey REST Service</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>it.polito.sistinfo.services.rest</param-value>

</init-param>

<load-on-startup>1</load-on-startup>

</servlet>

<servlet-mapping>

<servlet-name>Jersey REST Service</servlet-name>

<url-pattern>/rest/*</url-pattern>

</servlet-mapping>

</web-app>


Jersey+Eclipse - Client

A.A. 2012/2013

Jersey provides a client

library to consume REST

services

Clients can alternatively

exploit

Apache Http Client

Example

Google Directions API

Client c = Client.create();

c.setFollowRedirects(true);

WebResource r =

c.resource("http://maps.googleapis.com/maps/api/distancematrix");

MultivaluedMap<String, String> params = new

MultivaluedMapImpl();

params.add("origins", "cuneo");

params.add("destinations", "torino");

params.add("language", "it-IT");

params.add("sensor", "false");

//send the query

JSONObject responseAsJSON =

r.path("json").queryParams(params).get(JSONObject.class);

//print out the query

out.println(r.path("json").queryParams(params).getURI());

out.println("<br/>");

//print out the response

out.println(responseAsJSON.toString());


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