Web services tutorial for beginners

Enterprise IT is becoming the masterpiece of the information era. Your systems are distributed everywhere, both geographically and system wise. Web services are the super hero who can save you in this context.

What are Web services?


A web service is a

• piece of business logic, ( ex: java program)
• located somewhere on the Internet, (ex: servlet container like Apache Tomcat)
• that is accessible through standard-based Internet protocols such as HTTP or SMTP. (ex: SOAP)

Why Web services?

The promise of web services is to enable a distributed environment in which any number of applications, or application components, can inter-operate seamlessly among and between organizations in a platform-neutral, language-neutral fashion.

What are the features of Web services?

• XML-based

By using XML as the data representation layer for all web services protocols and technologies that are created, these technologies can be inter-operable at their core level. As a data transport, XML eliminates any networking, operating system, or platform binding that a protocol has.

• Loosely coupled

A consumer of a web service is not tied to that web service directly; the web service interface can change over time without compromising the client's ability to interact with the service. A tightly coupled system implies that the client and server logic are closely tied to one another, implying that if one interface changes, the other must also be updated. Adopting a loosely coupled architecture tends to make software systems more manageable and allows simpler integration between different systems.

• Coarse-grained

Object-oriented technologies such as Java expose their services through individual methods. An individual method is too fine an operation to provide any useful capability at a corporate level. Building a Java program from scratch requires the creation of several fine-grained methods that are then composed into a coarse-grained service that is consumed by either a client or another service. Businesses and the interfaces that they expose should be coarse-grained. Web services technology

provides a natural way of defining coarse-grained services that access the right amount of business logic.

• Ability to be synchronous or asynchronous

Synchronicity refers to the binding of the client to the execution of the service. In synchronous invocations, the client blocks and waits for the service to complete its operation before continuing. Asynchronous operations allow a client to invoke a service and then execute other functions. Asynchronous clients retrieve their result at a later point in time, while synchronous clients receive their result when the service has completed. Asynchronous capability is a key factor in enabling loosely coupled systems.

• Supports Remote Procedure Calls (RPCs)

Web services allow clients to invoke procedures, functions, and methods on remote objects using an XML-based protocol. Remote procedures expose input and output parameters that a web service must support. Component development through Enterprise JavaBeans (EJBs) and .NET Components has increasingly become a part of architectures and enterprise deployments over the past couple of years. Both technologies are distributed and accessible through a variety of RPC mechanisms. A web service supports RPC by providing services of its own, equivalent to those of a traditional component, or by translating incoming invocations into an invocation of an EJB or a .NET component.

• Supports document exchange

One of the key advantages of XML is its generic way of representing not only data, but also complex documents. These documents can be simple, such as when representing a current address, or they can be complex, representing an entire book or RFQ. Web services support the transparent exchange of documents to facilitate business integration.

This tutorial was prepared with the help of "Java Web Services" book published by O'reilly.