The Servlet specification says that, that the container should guarantee only
one instance of the servlet. However some of the container do maintain a
small of pool of servlet instances and manage them. For example there are 3
instances of a servlet in the pool, and if there are 300 requests, each
instance spawns off 100 threads for 100 requests.
I don't know how far this is true with Tomcat. In general you should not make
any assumptions about the number of instances of your servlet.
pradeep
-----Original Message-----
From: Milt Epstein [mailto:[EMAIL PROTECTED]]
Sent: Friday, March 23, 2001 8:17 PM
To: 'Tomcat'
Subject: Re: Why is my init method run twice?
On Fri, 23 Mar 2001, [iso-8859-1] Helgesen Hans Jørgen wrote:
> I'm new to this list, so please forgive me if this question has been raised
> before....
>
> I'm running Tomcat 3.2.1, Apache 1.3.12, java 1.2.2 and Redhat 6.2.
>
> I have a servlet to which I want to pass a single parameter via the web.xml
> file (below). I'm obtaining the parameter value by calling
> config.getInitParameter() in the init method of the servlet.
>
> This seems to work fine, the init method is called and the value obtained
OK
> when Tomcat is started.
>
> The problem is that when the first request for the servlet arrives, the
init
> method is run A SECOND TIME. This time the init parameter IS NOT AVAILABLE.
>
> My theory is that Tomcat calls the init method once for each thread, but if
> that is true, I would expect Tomcat to pass the init parameters each time?
>
> What is wrong?
How are you calling the servlet? I.e., via what URL?
Note that you can have different servlet definitions (servlet-name)
for the same servlet (i.e. servlet-class), and they are considered
different "instances", such that multiple instances of the servlet
class will be created (meaning init() will be called multiple times),
and only the parameters specified for each definition will be
available to that instance. It looks like you only have one servlet
definition, but still, if you call the servlet via the class name
directly, it will create a separate instance. E.g., from what you
have below, if you call /servlet/MyServlet and
/servlet/no.fellesdata.MyServlet, two separate instances will be
created.
> BTW, I can't get the servlet-mapping to work either. Any obvious errors?
What exact URLs are you trying? What happens when you try them?
Perhaps you haven't specified the appropriate directives in your
apache/tomcat conf file to tell apache to pass it to tomcat for that
URL.
> Here is my web.xml file:
> ------------------------
> <!DOCTYPE web-app
> PUBLIC "-//Sun Microsystems, Inc.//DTD Web Application 2.2//EN"
> "http://java.sun.com/j2ee/dtds/web-app_2_2.dtd">
>
> <web-app>
> <display-name>My test application</display-name>
> <description>
> Description of my test application
> </description>
>
> <servlet>
> <servlet-name>MyServlet</servlet-name>
> <description>
> Description of my servlet
> </description>
>
> <servlet-class>no.fellesdata.MyServlet</servlet-class>
>
> <init-param>
> <param-name>ConfigFile</param-name>
>
>
<param-value>/usr/local/jakarta-tomcat/webapps/poes/WEB-INF/myservlet.config
> </param-value>
> </init-param>
>
> <load-on-startup>5</load-on-startup>
> </servlet>
>
> <servlet-mapping>
> <servlet-name>MyServlet</servlet-name>
> <url-pattern>/MyServlet</url-pattern>
> </servlet-mapping>
>
> </web-app>
>
>
> And here is part of my servlet code:
> ------------------------------------
> public void init (ServletConfig config) throws ServletException
> {
> super.init(config);
> ....bla-bla-bla.....
> // Load configfile if it exists.
> configfile = config.getInitParameter("ConfigFile");
> if (null == configfile) {
> configfile = "default.value";
> }
> }
>
>
Milt Epstein
Research Programmer
Software/Systems Development Group
Computing and Communications Services Office (CCSO)
University of Illinois at Urbana-Champaign (UIUC)
[EMAIL PROTECTED]
