The original distrbuted Enterprise Application Development Platform. Microsoft and IBM have adopted most of these technologies in .NET environment. It is pity that Sun Microssystem, who is the original develops of this technology is geting sold to Oracle. I guess marketing hype is everything, also sun neglected the SMB marketplace.
The following resources have been useful for Java based enterprise development.
1.0 J2EE Enterprise Development
2.0 Apache Tomcat
3.0 BlueJay- SUN SDN
4.0 Comaprison of J2EE and .NET Technology
5.0 Jboss Application Server - Weblink