What is the Web service?
R) Web Service is an
application or a block of executable code exposed to the remote clients through
XML protocol. or
Web
services are
client and server applications that communicate over the World Wide Web’s (WWW)
Hypertext Transfer Protocol (HTTP). As described by the World Wide Web
Consortium (W3C), web services provide a standard means of interoperating
between software applications running on a variety of platforms and frameworks.
Types of Web Services
The two types of web services described in this post can be
distinguished as “big” web services and “Restful” web services.
“Big” Web Services
In Java EE 6, JAX-WS provides the functionality for “big”
web services. Big web services use XML messages that follow the Simple
Object Access Protocol (SOAP) standard, an XML language defining a message
architecture and message formats. Such systems often contain a machine-readable
description of the operations offered by the service, written in the Web
Services Description Language (WSDL), an XML language for defining interfaces
syntactically.
Restful Web Services
Restful web services are built to work best on the Web.
Representational State Transfer (REST) is an architectural style that specifies
constraints, such as the uniform interface, that if applied to a web service
induces desirable properties, such as performance, scalability, and modifiability
that enable services to work best on the Web. In the REST architectural style,
data and functionality are considered resources and are accessed using Uniform
Resource Identifiers (URIs), typically links on the Web. The resources are acted upon by
using a set of simple, well-defined operations. The REST architectural style
constrains architecture to client/server architecture and is designed to use a
stateless communication protocol, typically HTTP. In the REST architecture
style, clients and servers exchange representations of resources by using a
standardized interface and protocol.
The following principles encourage Restful
applications to be simple, lightweight, and fast:
· Resource identification through URI: A Restful web service exposes a set of
resources that identify the targets of the interaction with its clients.
Resources are identified by URIs, which provide a global addressing space for
resource and service discovery.
· Uniform interface: Resources are manipulated using a fixed set
of four create, read, update, delete operations: PUT, GET, POST,
and DELETE.PUT create a new resource, which can be then deleted by
using DELETE. GET retrieves the current state of a resource in
some representation.POST transfers a new state onto a resource.
· Self-descriptive messages: Resources are decoupled from their
representation so that their content can be accessed in a variety of formats,
such as HTML, XML, plain text, PDF, JPEG, JSON, and others. Metadata about the
resource is available and used, for example, to control caching, detect
transmission errors, negotiate the appropriate representation format, and
perform authentication or access control.
· Stateful interactions through hyperlinks: Every interaction with a resource is
stateless; that is, request messages are self-contained. Stateful interactions
are based on the concept of explicit state transfer. Several techniques exist
to exchange state, such as URI rewriting, cookies, and hidden form fields.
State can be embedded in response messages to point to valid future states of
the interaction.
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