Java Web Services [5/5]: REST and JAX-RS

Topic 5

REST and JAX-RS

Assoc.Prof. Dr. Thanachart Numnonda
www.imcinstitute.com
August 2010

Agenda
 What is REST?
 REST/HTTP Methods

 JAX-RS

2

REST : Definition [Wikipedia]
 Representational State Transfer
 a style of software architecture for distributed
hypermedia systems such as the World Wide
Web.
 was introduced and defined in 2000 by Roy
Fielding in his doctoral dissertation.
 Conforming to the REST constraints is referred
to as being ‘RESTful’.

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REST is ...
 An architectural style, not technology
– Client/server + Request/response approach.
 Everything is a RESOURCE.
 CRUD (Create / Read / Update / Delete)
 Stateless by nature (excellent for distributed
systems)
 Cacheable (naturally supported !)
 A great way to web-service !

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Architectural overview

6

Architectural overview

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HTTP request overview

8

HTTP request overview

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Everything is a resource …
 A resource is …
– A network-accessible data object or service
identified by an URI:
– Images,
– Documents (HTML, PDF, …),
– Geo-location,
– Weather

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Resource

 Collections
– http://portal/books/
 Members/Items:
– http://portal/documents/mybook.doc

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Characteristics of REST
 RESTful services are stateless
– Each request from client to server must contain all
the information necessary to understand the
request
 RESTful services have a uniform interface
– GET, POST, PUT, and DELETE.
 REST-based architectures are built from resources
(pieces of information) that are uniquely identified by
URIs
– In a RESTful purchasing system, each purchase
order has a unique URI 12

Characteristics of REST
 REST components manipulate resources by
exchanging representations of the resources
– For example, a purchase order resource can be
represented by an XML document.
– Within a RESTful purchasing system, a purchase
order might be updated by posting an XML
document containing the changed purchase order to
its URI
 REST-based architectures communicate primarily
through the transfer of representations of resources
– State is maintained within a resource representation
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REST/HTTP Methods

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CRUD to HTTP method mapping

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CRUD Operations are Performed
through “HTTP
method”+“Resource”

CRUD Operations HTTP method Resource
Create (Single) POST Collection URI
Read (Multiple) GET Collection URI
Read (Single) GET Entry URI
Update (Single) PUT Entry URI
Delete (Single) DELETE Entry URI

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HTTP Methods
 /books/
– POST - submit a new book
– GET - list all books
  /books/{isbn}/
– GET - get a book
– PUT - update a book
– DELETE - remove a book

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HTTP Methods: GET
 GET to retrieve information
 Retrieves a given URI
 Idempotent, should not initiate a state change
 Cacheable

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HTTP Methods: POST
 POST to add new information
 add the entity as a subordinate/append to the
POSTed resource
 Example
– POST /music/beatles

Adds the music specified in the
POSTDATA to the
list of music

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HTTP Methods: DELETE
 Remove (logical) an entity
 Example
– DELETE /songs/heyjude

Delete the song 'heyjude”
from the system

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HTTP Methods: POST
 POST to add new information
 add the entity as a subordinate/append to the
POSTed resource
 Example
– POST /music/beatles

Adds the music specified in the
POSTDATA to the
list of music

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Why REST ?
• Uniformity:
– URI is a uniform way to identify resources
– HTTP uniform interface to manipulate resources
• REST base services are easy to work with
– Do not need specialized API, just need to
understand HTTP and browser for
experimentation
• Scripting language friendly
– Easy to consume and develop
22

Advantages of REST
• Its architectural constraints when applied as a
whole, generate:
– Scalable component interactions
– General interfaces
– Independently deployed connectors
– Reduced interaction latency
– Strengthened security
– Safe encapsulation of legacy systems

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REST vs “Big” Web Services
• “Big” web service
– Few URIs (nouns), many custom methods
(verbs)
• musicPort.getRecordings(“beatles”)
– Uses HTTP as transport for SOAP messages
• RESTful web service
– Many resources (nouns), few fixed
methods(verbs)
• GET /music/artists/beatles/recordings
– HTTP is the protocol
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JAX-RS (JSR-311) : Goals

• POJO-based,
• HTTP-centric,
• Format independent,
• Container independent,
• Availability as standalone and enterprise platforms.

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JAX-RS: Address-ability through URI

• A Web service exposes data as resources
• A resource is exposed through a URI
• Resources are “plain old” Java classes and methods
• The annotation @Path exposes a resource
• Think resources and URIs using Java classes and
@Path

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POJO + Annotation = JAX-RS resource

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Reading the catalog

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Reading the catalog item

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Address-ability through HTTP Methods

• Methods: what are the HTTP methods?
• HTTP methods implemented as Java methods
annotated with
– @POST
– @GET
– @PUT
– @DELETE

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Uniform interface: methods on root
resources
@Path(“/books/”)
class books {
@POST <type> create(<type>) { ... }
@GET <type> get() { ... }
}
@Path(“/books/{isbn}/”)
class book {
@GET <type> get(...) { ... }
@PUT void update(...) { ... }
@DELETE void delete(...) { ... }
}
Java method name is not significant
The HTTP method is the method 32

Leading JAX-RS implementations

• Glassfish Jersey project
• RESTEasy(JBoss)
• Apache CXF (Apache Software Foundation)
• Wink (ASF incubation project)
• Restlet(NoeliosTechnologies)

33

Resources
 Some contents are borrowed from the presentation
slides of Sang Shin, Java™ Technology Evangelist,
Sun Microsystems, Inc.
 JAX-RS… and the REST will follow, Guy Nir, Java
Edge 09

34

Thank you

thananum@gmail.com
www.facebook.com/imcinstitute
www.imcinstitute.com

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Java Web Services [5/5]: REST and JAX-RS

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