Web Service:
·
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.
·
Web services are characterized by their great
interoperability and extensibility, as well as their machine-processable
descriptions, thanks to the use of XML.
·
Web services can be combined in a loosely coupled way to achieve
complex operations. Programs providing simple services can interact with each
other to deliver sophisticated added-value services.
Loosely Coupled:
In computing and systems
design a loosely coupled system is one in which each of its components has, or makes use of, little or no knowledge of the
definitions of other separate components.
Subareas include the coupling of classes, interfaces, data, and services.[1] Loose
coupling is the opposite of tight coupling.
Types of Web
Services in Java
1.
Java API for XML Web Services (JAX-WS)
·
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.
·
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.
A SOAP-based design must include the following elements.
·
A formal contract must be established to
describe the interface that the web service offers.
·
WSDL can be used to describe the details of the
contract, which may include messages, operations, bindings, and the location of
the web service
·
The architecture must address complex
nonfunctional requirements. Examples include transactions,
security, addressing, trust, coordination, and so on.
·
The architecture needs to handle asynchronous
processing and invocation.
1.
Java API for RESTful Web Services (JAX-RS).
In Java EE 6, JAX-RS provides
the functionality for Representational State Transfer (RESTful) web services.
RESTful web services, often better
integrated with HTTP than SOAP-based services are, do not require XML messages
or WSDL service–API definitions.
A RESTful design may be
appropriate when the following conditions are met.
·
The web services are completely stateless. A
good test is to consider whether the interaction can survive a restart of the
server
·
A caching infrastructure can be leveraged for
performance. If the data that the web service returns is not dynamically generated
and can be cached, the caching infrastructure that web servers and other
intermediaries inherently provide can be leveraged to improve performance.
·
The service producer and service consumer have a
mutual understanding of the context and content being passed along.
·
Bandwidth is particularly important and needs to
be limited.
·
Web service delivery or aggregation into
existing web sites can be enabled easily with a RESTful style
·
Developers can use such technologies as JAX-RS
and Asynchronous JavaScript with XML (AJAX) and such toolkits as Direct Web
Remoting (DWR) to consume the services in their web applications.
