IMP - idempotent and non idempotent http methods ?

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Discuss various approaches to develop SOAP based web service ?

There are 2 approaches : Contract-first & Contract-last. 
Contract-first starts with defining first XML schema / WSDL and then creating the Java classes based on them. In Contract-last approach Java classes are defined first than WSDL is generated from that.

What are Tools/API are there for developing/testing web service?

Testing Tools for Web Service : SoapUI for SOAP Web Service, Firefox plugin for testing RESTFul Services.
REST APIs : Spring REST Web Service using MVC, Jersey API, CFX, Axis, Restlet etc. 
SOAP APIs : Axis, Spring Web Service etc

What are Tools/API are there for developing/testing web service?

Testing Tools for Web Service : SoapUI for SOAP Web Service, Firefox plugin for testing RESTFul Services.
REST APIs : Spring REST Web Service using MVC, Jersey API, CFX, Axis, Restlet etc. 
SOAP APIs : Axis, Spring Web Service etc

What is REST ?

REST is architectural style for building web service using HTTP protocol, where web services are treated as resources and some basic HTTP methods like GET, POST, DELETE are used
to identify standard action on resources.RESTful web API (also called a RESTful web service) is a web API implemented using HTTP and the REST principles.

What are the different application integration styles?

There are a number of different integration styles like
1. Shared database
2. batch file transfer
3. Invoking remote procedures (RPC)
4. Exchanging asynchronous messages over a message oriented middle-ware (MOM).

What is meant by JAX-WS and JAX-RS?

Java API for XML Web Services(JAX-WS)
Java API for RESTful Web Services (JAX-RS)