Transcript REST Web Services Characteristics Client

Web Services using REST &
JAX-WS
Prepared By : Monika Darji
REST stands for REpresentational State Transfer
• The term Representational State Transfer was introduced
and defined in 2000 by Roy Fielding in his doctoral
dissertation
• It is an architectural style, not a toolkit.
• Resources are identified by uniform resource identifiers (URIs)
• Resources are manipulated through their
Representations.
• Messages are self-descriptive and stateless
• Example of a RESTful request:
POST /users HTTP/1.1
Host: myserver
Content-Type: application/xml
<?xml version="1.0"?>
<user>
<name>Robert</name>
</user>
Prepared By : Monika Darji
The basics
REST defines a set of architectural principles by which you
can design Web services that focus on a system's
resources, including how resource states are addressed
and transferred over HTTP by a wide range of clients
written in different languages. If measured by the
number of Web services that use it, REST has emerged
in the last few years alone as a predominant Web
service design model. In fact, REST has had such a
large impact on the Web that it has mostly displaced
SOAP- and WSDL-based interface design because it's a
considerably simpler style to use.
A concrete implementation of a REST Web service follows
four basic design principles:
1. Use HTTP methods explicitly.
2. Be stateless.
3. Expose directory structure-like URIs.
4. Transfer XML, JavaScript
Object Notation (JSON), or
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both.
Use HTTP methods explicitly.
REST asks developers to use HTTP methods explicitly and
in a way that's consistent with the protocol definition.
This basic REST design principle establishes a one-toone mapping between create, read, update, and delete
(CRUD) operations and HTTP methods. According to
this mapping:
* To create a resource on the server, use POST.
* To retrieve a resource, use GET.
* To change the state of a resource or to update it, use
PUT.
* To remove or delete a resource, use DELETE.
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Be stateless
•
A REST Web service application (or client) includes
within the HTTP headers and body of a request all of
the parameters, context, and data needed by the
server-side component to generate a response.
Statelessness in this sense improves Web service
performance and simplifies the design and
implementation of server-side components because
the absence of state on the server removes the need
to synchronize session data with an external
application.
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Expose directory structure-like URIs\
REST Web service URIs should be intuitive to the point where
they are easy to guess. Think of a URI as a kind of selfdocumenting interface that requires little, if any, explanation
or reference for a developer to understand what it points to
and to derive related resources. To this end, the structure of
a URI should be straightforward, predictable, and easily
understood.
Transfer XML, JSON, or both
The last set of constraints that goes into a RESTful Web
service design has to do with the format of the data that the
application and service exchange in the request/response
payload or in the HTTP body. This is where it really pays to
keep things simple, human-readable, and connected.
Prepared By : Monika Darji
REST Web Services Characteristics
• Client-Server: a pull-based interaction style: consuming
components pull representations.
• Stateless: each request from client to server must contain all the
information necessary to understand the request, and cannot take
advantage of any stored context on the server.
• Cache: to improve network efficiency responses must be capable of
being labeled as cacheable or non-cacheable.
• Uniform interface: all resources are accessed with a generic
interface (e.g., HTTP GET, POST, PUT, DELETE).
• Named resources - the system is comprised of resources which are
named using a URL.
• Interconnected resource representations - the representations of
the resources are interconnected using URLs, thereby enabling a
client to progress from one state to another.
• Layered components - intermediaries, such as proxy servers,
cache servers, gateways, etc, can be inserted between clients and
resources to support performance,
security, etc.
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Examples
• REST can be found in many places on the public Web:
• The 'blogosphere' — the universe of weblogs — is
mostly REST-based, since it involves downloading XML
files (in RSS, or Atom format) that contain lists of links to
other resources;
• The Atom Publishing Protocol for publishing to blogs is
considered the canonical RESTful protocol;
• Amazon.com's S3 is their only truly REST offering;
• OpenStreetMap offers a REST interface
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RESTful Web Services versus SOAP Web Services
Message Format
Interface Definition
Transport
REST
XML
none
HTTP
SOAP
XML inside a SOAP Envelope
WSDL
HTTP, FTP, MIME, JMS, SMTP
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JAX-WS
• The Java API for XML Web Services (JAX-WS)
is a Java programming language API for
creating web services. It is part of the Java EE
platform from Sun Microsystems. It is part of the
Java Web Services Development Pack.
• The Reference Implementation of JAX-WS is
developed as an open source project and is part
of project GlassFish, an open source Java EE
application server.
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Service Oriented Architecture(SOA)
• Service-oriented architecture (SOA) is an evolution of
distributed computing based on the request/reply design
paradigm for synchronous and asynchronous
applications. An application's business logic or individual
functions are modularized and presented as services for
consumer/client applications. What's key to these
services is their loosely coupled nature; i.e., the service
interface is independent of the implementation.
Application developers or system integrators can build
applications by composing one or more services without
knowing the services' underlying implementations. For
example, a service can be implemented either in .Net or
J2EE, and the application consuming the service can be
on a different platform or language.
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Characteristics of SOA
* SOA services have self-describing interfaces in platformindependent XML documents. Web Services Description
Language (WSDL) is the standard used to describe the
services.
* SOA services communicate with messages formally
defined via XML Schema (also called XSD).
* SOA services are maintained in the enterprise by a registry
that acts as a directory listing. Applications can look up
the services in the registry and invoke the service.
Universal Description, Definition, and Integration (UDDI)
is the standard used for service registry.
* Each SOA service has a quality of service (QoS)
associated with it. Some of the key QoS elements are
security requirements, such as authentication and
authorization, reliable messaging, and policies regarding
who can invoke services.
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The ROLE OF WSDL in SOA
WSDL is the interface definition language (IDL) that defines
the interactions among SOA components. It provides a
standard language for describing how to communicate with
a component.
Following figure shows the role of WSDL for SOA..The
deployment takes place in Web Services Platform
subsystem.
The top-level class depicted in that subsystem is
ServiceDeployment. Each instance of ServiceDeployment
corresponds to a Web service that is deployed on this
platform.The ServiceDeployment contains both an
operation (taken from the WSDL interface description) and
a Java method. A Web service deployment defines a
relationship between a WSDL interface description and a
Java implementation of that description.
Prepared By : Monika Darji
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The ROLE OF SOAP in SOA
• The role of SOAP in SOA is to provide a
concrete implementation,or binding, for the
WSDL interfaces.
Prepared By : Monika Darji