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From Michael Duffy <duff...@yahoo.com>
Subject Re: Problem using JDBC resource during HttpServlet.init()
Date Wed, 25 Jun 2003 18:52:54 GMT

I've got a JDBC data source that I get via JNDI lookup
using Tomcat.  My servlet has <load-on-startup> set to
2, and I haven't seen this problem with the "not
bound" problem.

I define a context.xml that has a <Resource> tag and
its <ResourceParams> children.  During development, I
deploy the app-name.war file using the Ant Catalina
<deploy> task, which lets me specify a app-name.xml
context file.

When I install the app, I put the app-name.war and
app-name.xml context file in TOMCAT_HOME/webapps. 
Tomcat picks up both.

--- Gwyn Fisher <gwyn@gwynfisher.com> wrote:
> I am working on a webapp that consists of an HTTP
> Servlet and a bunch of
> files that are served by the servlet in response to
> query parameter-based
> requests, i.e. they're not static files served by
> the Default servlet. We
> are packaging the servlet and its related files into
> a WAR to make upload
> and deployment at our hosting provider a rational
> process.
> 
> In order for the servlet to be able to serve its
> files (amongst the other
> things it does), the WAR needs to be unpacked by the
> autoDeploy setting,
> which we believe means that we can't define a
> context for it, either via an
> <app>.xml definition, or a <Context> element in the
> server.xml, as in the
> presence of a defined context, Tomcat explicitly
> does not unpack WAR files.
> 
> The servlet overrides init() in order to be able to
> single thread through
> database initialization code without having to
> synchronize anywhere else.
> Within the init() method we are attempting to
> connect to a JDBC resource
> that is defined within the <DefaultContext> (we're
> using MySQL, but I don't
> believe that's important for the purposes of this
> question).
> 
> The connection is accomplished using the normal
> sequence of operations:
> 
>     Context context = new InitialContext();
>     DataSource ds =
>
(DataSource)context.lookup("java:comp/env/jdbc/MySQLDB");
>     Connection connection = ds.getConnection();
> 
> If I do not specify that the servlet should be
> loaded on Tomcat startup,
> everything works fine.
> 
> If, however, we add the <load-on-startup> element to
> the servlet's
> definition in web.xml, the lookup() operation throws
> an exception saying
> "jdbc is not bound in this context".
> 
> After searching the news groups, we added a
> <resource-ref> element to
> web.xml:
> 
>     <resource-ref>
>         <res-ref-name>jdbc/MySQLDB</res-ref-name>
>         <res-type>javax.sql.DataSource</res-type>
>         <res-auth>Container</res-auth>
>     </resource-ref>
> 
> Upon restarting Tomcat, the servlet now passes the
> lookup() operation, but
> receives an exception when attempting to open a
> connection using
> getConnection(): Cannot load JDBC driver class
> 'null'.
> 
> In both cases, however, when a user makes a request
> of the servlet, the
> init() method is again invoked and this time
> everything works as planned.
> Both the lookup() and the getConnection() calls
> succeed.
> 
> So my questions are as follows:
> 
> - am I correct in my understanding that if you
> define a Context for a WAR,
> the archive is never unpacked by Tomcat? And if so,
> I wonder if anybody
> could explain why? The reason for asking this
> particular question is that in
> the presence of an unpacked WAR and a defined
> Context (either <app>.xml or a
> <Context> element within server.xml), the
> load-on-startup tag produces the
> desired result, i.e. everything in the JDBC
> initialization works as planned.
> 
> - why, when using autoDeploy, if the JDBC
> initialization works the 2nd time
> through init() -- following a user request of the
> servlet -- does it not
> work the 1st time through -- during Tomcat startup?
> 
> - or am I just being terminally stupid and missing
> something really obvious?
> 
> Many thanks for any help received,
> Gwyn Fisher.
> 
> 
>
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