Cortlandt wrote

> ... That is why, as I did mention, I'm
>switching to Enhydra.    I've searched the on-line documentation and
>asked around and I still not sure how Tomcat, JServ, and Endyra
>relate.

Apache JSERV from http://java.apache.org is a servlet engine that
is used together with the Apache web server to implement dynamic web
pages with Java Servlets. It uses an Apache module called mod_jserv
to connect the httpd processes with the (separate) jserv process.

Apache takes care of static web pages, CGI programs, etc, and passes
requests for certain types of requests to the jserv process, which
loads and or (re)invokes Java Servlets to generate the http response.

Jakarta TOMCAT from http://jakarta.apache.org is also a servlet engine,
however, besides implementing a newer version of the Java Servlet API,
it also offers Java Server Pages. JSP allows adding Java code to HTML
pages (similar to ASP which adds Visual Basic to HTML pages?). The JSP
engine in Tomcat generates Java source code for the JSP page, compiles
it and runs the resulting class file whenever the URL is accessed. I'm
not 100% sure, but I believe that the class files generated for the JSP
pages are also Java Servlets.

As far as I recall, Tomcat also has some Apache module (mod_jk) that
allows it to integrate with Apache, but it also can be run standalone
as it has built-in http server capabilities. However, I believe, that
most Tomcat installations would use it in conjunction with Apache as
Apache is more optimized and feature rich for general web serving.

Lutris ENHYDRA from http://www.enhydra.org is slightly more than just
a servlet engine. It contains Jakarta Tomcat and thus provides servlet
and JSP for dynamic web pages, but it also offers its own infrastructure
to help building web applications. Older versions of Enhydra used JDDI,
a technique similar to JSP, where you embed Java code in HTML pages (but
those were precompiled to servlets, not compiled at run time). The newer
Enhydra versions use XMLC dealing with dynamic web pages to get a better
separation of HTML and Java source code (i.e. layout and logic). An XML
compiler generates Java classes for HTML pages. Those classes are used
by the web application to generate dynamic output to the browser. In the
HTML page you can use "id" tags to markup those sections that the web
application can modify at run time.

Enhydra includes an http server for running standalone, but also offers
a module called Enhydra Director to interface it with web servers like
Apache, Netscape or Microsoft. Same idea as with JServ and Tomcat: use
the native web server for static pages and Java for dynamic content.

Oh, the upcoming Enhydra Enterprise will also add J2EE infrastructure
to beef up the alphabet soup. Things like the EJB (Enterprise JavaBeans)
container Jonas from Honeywell, for example. If you consider Servlets
or JSP or JDDI or XMLC confusing, then you haven't seen J2EE yet ;-)

Hope this helps to shed some light.

Lars.


PS: The longer you look at the trendy web-technology soup du-jour, the
more you get the impression how simple, robust and efficient those good
old COBOL-IMAGE-VPLUS applications are ;-)

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