Web Service Tutorial

In this web service tutorial, we will see the introduction of webservices in java and some jargons of web services.

Webservices in java are used everywhere nowadays. When human interacts with any web page, it involves request and response via HTML. When you interact with the webpage, browser sends a request and then renders response and shows in form of HTML. Similarly, web services also involve request and response but in the form of XML or JSON or plain text. It generally used for other applications or programs to consume and make use of information.

For example:
You are creating a website which shows weather information of important cities in the world. You can actually consume already exposed web services and get the data for the cities. You will get the response in form of XML or JSON, you can parse it and show it on your website.

Let’s go to more formal definition now:

Web service is a way of communication that allows interoperability between different applications on different platforms, for example, a Java based application on Windows can communicate with a .Net based one on Linux. The communication can be done through a set of XML messages over HTTP protocol.Web services are browsers and operating system independent service, which means it can run on any browser without the need of making any changes. Web Services take Web-applications to the Next Level.

The World Wide Web Consortium (W3C) has defined the web services. According to W3C, “Web Services are the message-based design frequently found on the Web and in enterprise software. The Web of Services is based on technologies such as HTTP, XML, SOAP, WSDL, SPARQL, and others.”
Let’s say, you are a Java developer and you can publish your functions on internet or LAN through java web service so any other developer(let’s say .Net developer) can access your function.

You can go through web services interview questions for interview questions on webservices in java.

Why you need to learn web services:

Deployability :

Web Services are deployed over standard Internet technologies. This makes it possible to deploy Web Services even over the firewall to servers running on the Internet on the other side of the globe. Also thanks to the use of proven community standards, underlying security (such as SSL) is already built-in.

Some jargons used in Webservices in java:

Simple Object Access Protocol(SOAP):

Web Service Description Language(WSDL):

WSDL stands for Web Service Description Language. It is an XML file that describes
the technical details of how to implement a web service, more specifically the URI,
port, method names, arguments, and data types. Since WSDL is XML, it is both
human-readable and machine-consumable, which aids in the ability to call and bind to
services dynamically.

Elements of WSDL are:

Description:
It is the root element of a WSDL 2.0 file. It usually contains a set of namespace declarations which are used throughout the WSDL file. 

Types:
The WSDL types element describes the data types used by your web service.Data types are usually specified by XML schema.It can be described in any language as long as your web services API supports it.

Binding:
The WSDL binding element describes how your web service is bound to a protocol. In other words, how your web service is accessible. To be accessible, the web service must be reachable using some network protocol. This is called “binding” the web service to the protocol.

Interface:
The WSDL interface element describes the operations supported by your web service.It is similar to methods in programming language.The client can only call one operation per request.

Service:
It describes the endpoint of your web service. In other words, the address where the web service can be reached.

Endpoint:
The endpoint element describes the address of the web service. The endpoint binding attribute describes what binding element this endpoint uses.i.e. protocol with which you will access web service. The address attribute describes the URI at which you can access the service.

Message:
The message element describes the data being exchanged between the Web service providers and consumers.

Sample WSDL file:

Universal Description, Discovery and Integration(UDDI):

UDDI stands for Universal Description, Discovery, and Integration.It is a directory service. Web services can register with a UDDI and make themselves available through it for discovery

Web service design approaches: