Various
levels of complexity ;)
At one level
the answer is, they different stupid.
At a higher
level, the answer is, not much, same thing, different
flavor.
In general Java has cornered the brand name
"application server", and there are many.
On the spectrum, it moves through web pages,
they become intelligent web pages (CGI, PHP, servlets), they become remote
procedure calls (SOAP and Web services), they become managed beans (little
applications) called the application server.
However that sequence is not orderly, a good
PHP developer may knock the pants of a Java servlet developer and a Java
servlet developer may run rings around an EJB coder... it depends on
what you doing, and how good you are with various tools.
There are some nice distinguishing
charateristics.
When a system switches from delivering web a
pages to doing remote procedure calls.
When the client is a browser, or when the
client becomes another application.
Some technology feels very much like a tool,
others you definitely know you living in someone elses system
(world).
Some systems mix, in others its near impossible
to introduce another system.
The POJO cult versus the EJB cult
The KISS (keep it simple stupid) versus
complexity cult.
There is no short cut, you need to look at em
all...
The one you looking at is an anchor, you just
got to know Apache httpd.
The other one thats worth looking at is
Tomcat.
These two systems mix well, and will probably
cover 95% of your needs.
That other 5% is a difficult choice... SOAP
versus EJB versus POJO etc.
Its a good question, you need to learn em, or
else you will never make the right choices.
Choosing incorrectly, can get one into big
trouble, round peg, square hole problems that only emerge after 6 months of
work.
They are certainly all interesting, and once
you have studied them, you see the patterns.
Dont learn em, and they can bite
;)
Have fun...
