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From "Craig R. McClanahan" <>
Subject Re: tomcat 3.x vs. tomcat 4.x
Date Sun, 22 Oct 2000 12:48:07 GMT
Charles Sabourdin wrote:

> will the developpement under tomcat 3.x be exportable
> for 4.x ?
>  I suppose your are gonna says off course but I still
> need confirmation.
> ;-)

The following notes on compatibility should help reassure you :-)

Applications developed to run under Tomcat 3.x (that is, based on the
servlet 2.2 and JSP 1.1 specifications) should run under Tomcat 4.x
(based on servlet 2.3 and JSP 1.2) unmodified, unless they rely on:
* Bugs in the current implementation.
* Rely on behavior of Tomcat 3.x that was not specified in 2.2/1.1
  but has been clarified under 2.3/1.2 (a few small issues).
* Use a web.xml file that does not conform to the DTD (Tomcat 3.x
  did not check this unless you were using tag libraries; Tomcat 4.0
  uses a validating XML parser to read this file).
Thus, courtesy of the backwards compatibility of the new spec versions,
you should be able to run essentially all existing web apps under Tomcat
4.x.  As an example of this, I've had no problem running Struts
applications under 4.0, without even recompiling.  (NOTE:  2.3
containers are *required* to accept web.xml descriptors in the 2.2

Server configuration for Tomcat 4.x (in server.xml) is very similar to
3.x, but will require small tweaks.  In addition, Tomcat 4.0 restores
the ability to provide global defaults for all web apps in conf/web.xml
(the same way this was done in 3.1).

Web connector configuration will be different (and dramatically
simplified) in Tomcat 4.x, because the connectors are being built to be
web-app aware.  Thus, you will not have to configure things twice --
once in web.xml and once in your Apache config, for example -- when they
fall outside the bounds of the default configuration files that Tomcat
creates when it starts.

System components, on the other hand (i.e. things implemented as
RequestInterceptors or ContextInterceptors under 3.2) will need to be
re-implemented for Tomcat 4.x.  The internal architecture is
substantially different.

Craig McClanahan

See you at ApacheCon Europe <>!
Session VS01 (23-Oct 13h00-17h00):  Sun Technical Briefing
Session T06  (24-Oct 14h00-15h00):  Migrating Apache JServ
                                    Applications to Tomcat

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