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Introduction toRepresentational State

Transfer(REST)

and the Restlet FrameworkPhilip Johnson

Collaborative Software Development Laboratory

Information and Computer SciencesUniversity of Hawaii

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Agenda Concepts:•Why REST?•REST principles•What is Restlet?

Restlet-DateService:•Download distribution•Command line usage•build.xml•The server-side code•The client-side code• JUnit tests + Jacoco•Building the jars

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Why REST? The web according to most webapp frameworks:

Server

Server

Server

Server

Wicket, RoR, etc all designed for human-computer interaction. (as well as AJAX, CSS, HTML, Fonts, JQuery, Javascript, etc.)

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Why REST? But there is another kind of interaction:

Server

Server

Server

Server

Most HCI mechanisms are not well-designed for computer-computer interaction.

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Why REST? Computer-Computer interaction can be very powerful:•Provide “mashups” of data from different sources.•Support automated crawling of the web (i.e. Google)•Realize the full potential of the web.

But to do this, we need a way for computers to easily and expressively communicate with each other.

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REST Representational State Transfer (REST) is an “architectural style” defined by Roy Fielding. •The concepts of REST are independent of the web, but the web is well-suited to REST.

Simplistically, a “RESTful architecture” includes:•Resources (things) with •Unique ids (URLS) that can come in many•Representations (text, html, json) that you operate on with•Verbs (GET, PUT, DELETE, POST)

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REST in a nutshell URLs must name resources. They are nouns:•http://cnn.com/story/hawaii/fireworks

Not verbs:•http://cnn.com/addComment?name=fireworks

Use operators (verbs) such as GET, PUT, POST, DELETE to operate on resources (nouns):•GET http://cnn.com/story/hawaii/fireworks•PUT http://cnn.com/story/hawaii/explosion•POST http://cnn.com/story/hawaii/nye/comments•DELETE http://cnn.com/story/hawaii/nye

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REST in a nutshell Most common operators (verbs):•GET:

-retrieve a representation of a resource (without changing it).

•PUT: -create or replace a resource by supplying a representation of it.

•DELETE:-ensure that a given resource is no longer present.

•POST:-augment a resource with additional information by supplying a representation of that info.

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REST in a nutshell Representations•As an external user, you cannot manipulate resources directly. •Instead, you manipulate “representations” of that resource. -Many people can “get” a representation of a single resource.-The same resource can be represented in many different ways.

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The web and REST The web’s primary protocol (HTTP) is tailor-made for RESTful architectures. •Unique IDs for resources (URIs)•Verbs (HTTP operators)•Multiple representations (Media types)

But many (most) web applications do not implement REST!•Use of GET for everything.•URLs that indicate actions, not things. •Many other subtle ways to violate REST.

-See readings for more details.

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REST is best for computer-computer

interaction

Server

Server

Server

Server

The jury is still out on whether REST is always best for human-computer interaction.

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Restlet A Java framework for implementing REST systems.

Operators, Resources, Representations, are all “first class” entities in Restlet.

Highly “pluggable” implementation to support extensibility and interfaces to other web technologies•Atom, Freemarker, GWT, JAAS, Jackson, JavaMail, JAXB, Jetty, JSON, Lucene, OData, RDF, Rome, Spring, WADL, SSL, XML, etc.

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Restlet-DateService A “hello world II” Restlet application•Simple to install and run•Illustrates basic RESTful client and server using Restlet.•Shows unit testing with JUnit.•Packaging of client and server into jars.

Does not show:•PUT, POST, DELETE operators.•Authorization and authentication.•Templates URLs.•Restlet extensions•Automatic media type negotiation