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Message-ID: <3ECBBA2E.1000303@gefionsoftware.com>
Date: Wed, 21 May 2003 10:41:02 -0700
From: Hans Bergsten <hans@gefionsoftware.com>
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To: Tomcat Developers List <tomcat-dev@jakarta.apache.org>
Subject: Re: Help: Servlet container vs JSP container vs servlet engine vs
 JSP engine
References: <OF450E5968.55CA6845-ON86256D2D.005E9C9F@corp.teradyne.com>
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henrik.bentel@teradyne.com wrote:
> ok, so I thought I had a pretty good understanding of how it all works.
> But then the more different documentation, books and articles I read, the
> less sure I get about this one(read subject)
> 
> The way I see it:
> 1. A servlet/and JSP container contains a Servlet and JSP engine.
> 2. Servlet engine "runs" servlet and JSP engine "runs" JSPs(catalina and
> Jasper 2).
> 3. When a servlet forwards to a different resource such as a JSP, it the
> task of the servlet/JSP container help doing this(not the engines).
> 4. A JSP container can't exist without being a servlet container, but a
> servlet container can exist without supporting JSPs(Its a servlet container
> or both).
> 5. A JSP engine could exist without a servlet container and a servlet
> engine.
> 
> The words engine and container is used interchangably all over the place.
> The official specs tend to only refer to containers, saying JSP run in the
> servlet container(since JSP are really just servlets, although a special
> kind). In tomcat documentation cataline is referred to as both the
> container and an engine. Is it one or both?? Which is what and what is
> where and where is which?!?
> 
> Hope someone can shed some light on this

In general, "engine" is the old term for what's now called a
"container" (renamed when the servlet and JSP specs got included in the
J2EE umbrella spec). The servlet spec describes the "servlet container",
the JSP spec the "JSP container"; together these two containers are also
referred to as the "web container".

The "engine" term has a special meaning in Catalina. It's a container
for a Service, handling all requests directed to one or more Connectors
for the Service, see the Tomcat 4 docs for more info:

   <http://jakarta.apache.org/tomcat/tomcat-4.0-doc/config/index.html>

In many books and articles, the terms "engine" and "container" (with
the prefixes "servlet", "JSP" or "web") are often used interchangably,
as you have noticed.

Hans
-- 
Hans Bergsten                                <hans@gefionsoftware.com>
Gefion Software                       <http://www.gefionsoftware.com/>
Author of O'Reilly's "JavaServer Pages", covering JSP 1.2 and JSTL 1.0
Details at                                    <http://TheJSPBook.com/>


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