Server User Manual

6 Developing Applications for J2EE Servers
Why are J2EE applications desirable?
was “served up” by a server. This approach initially promised improved scalability and
functionality.
Through hard experience, however, the development community learned that building
and maintaining a flexible distributed system is very difficult using the client-server
model. For example, the business logic of the application was in the client application.
Every time that logic needed modification, the revised application had to be installed on
every client machine in the enterprise. Maintenance became a nightmare. These
applications also had to manage transactions, be concerned with security, and process
the data efficiently, all the while presenting an attractive, easy-to-understand interface
to its users. Few developers have talents in all these areas. While a client-server
architecture might be adequate for some environments, most of today’s global
companies demand considerably more than the client-server model can deliver.
Once the limitations of the client-server approach became apparent, the development
community began seeking a better way. The result is the multi-tier model.
In the multi-tier model, the logic involved in presenting the user interface of the
application to the user lives on the middle tier. The business logic is now on the middle
tier also. When changes are needed, they can be updated in one place instead of on
each client machine.