Can someone explain the difference between a web service and web app? and also if i am making a J2me app and want a user to get authenticated when he sends a login request to the server which 1 should i use? Do both perform all functions automatically without human intervention and how do u access the service/app from a j2me app? when does ejb come into the picture? THANKS A LOT TO ANY1 WHO CAN ANSWER ALL THESE QUERIES!!
Web service is a service that is a component used/consumed by application/web application. Service is using open protocols and can be discovered by Universal Description, Discovery and Integration (UDDI). XML is used for communication between applications and services. You may seen web service as weather cast on website, sport results, news and more that are produced by an organization and used by millions of website to present these data to visitors without need to create them.
I'm not exactly sure what your intentions with JME, but this can go in both directions you can have application that will directly connect to service and retrieve data (RSS and Atom feeds) or in case of secure content you would have midlet first connect to web application for user verification and then enable him/her to get protected data.
As with anything you would need to use HttpConnection to reach either web application or service.
Use of EJB is your decision. If you want to know more about EJB you may consider to read Head First EJB