It's neither a language nor a collection of technology (at least not like .NET is a collection of technology). Instead, it's more a design
pattern than anything else.
(This response got long, so I broke it down into a couple of sections)
Overview The hallmark of J2EE is Enterprise JavaBeans. EJBs provide the ability to run processes on remote servers and serve as the middle tier in the J2EE framework. There are two types of EJBs: Entity and Session. Entity EJBs are used primarily to communicate with the database, while Session EJBs are used to hold business logic. EJBs run on an "Application Server."
The front end for the J2EE is JSP/Servlet technology. Much like ASP, these provide dynamic HTML to the user. These run on a "Web Server."
The back end is any database that you choose (even Access, if you want
) This is the "Database Server."
Data Flow User uses Web browser to access JSP/Servlets
JSP/Servlets send data to Business Logic located in Session EJBs
Session EJBs use the data exposed by Entity EJBs.
Entity EJBs interface with the Database.
The Database is a "dumb" database in that its only role is to store data. All business logic happens at the Session EJB level (this means no reliance on stored procedures! Access dosen't have them anyway
)
The data flows in reverse back to the
JSP, which generates the dynamic HTML and presents the results back to the user.
Technologies A common JSP/Servlet engine is Apache
Tomcat. It's free, so I'm not sure what other ones are out there. (IBM's HTTP Server is just Tomcat re-labeled, although I think they've made a few improvements on the product.)
The middle layer has more vendors. IBM WebSphere and BEA Weblogic are two of the front runners in the Application Server realm, although
JBoss is a popular free one. (There's also HP Bluestone, but I think that is no longer a supported product. And, in my opinion, this is not a bad thing.
)
Of course, at the database layer, there a a plethora of choices. Oracle, MySQL, and MS SQL Server are popular choices (MySQL being free, Oracle and SQL Server competing with each other for market dominance). Other choices include Sybase, IBM's DB2, Access (!! if you're low volume
and crazy, but I've seen it), and others.
Hope this clears things up. I tend to be long-winded, so if you have any questions, just ask. (And I'll probably get long-winded again, but, hey.)
