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From Bob Marcum <bmar...@BCScomputers.com>
Subject Re: Seeking the right solution to java.lang.ClassNotFoundException: com.mysql.jdbc.Driver
Date Mon, 20 Jul 2009 22:19:13 GMT
Responding to both ...

Being guided by your judgements I have made a few adjustements and re-tried.
1. I removed the mysql driver jar from my jse/jre/lib/ext
2. I confirmed hibernate3.jar is in myapp/WEB-INF/lib.  It has always been there.
3. I put mysql-connector-java-3.1.10-bin.jar back into WEB-INF/lib
4. I did a "find" scan of my system, looking for other copies of both hibernate3.jar and mysql-connector-java-3.1.10-bin.jar
to
confirm there are no other copies which could be in classpath. I found no other copies which
could be in classpath, given the
tools I am using.  well ... wait.  There is a link to the mysql driver jar in hibernate-3.0's
own lib directory.  Hmmmm.  I wonder
if that could be confusing hibernate?  Since it is a link, I must have put it there a year
or so ago.  I did not remove the link. 
5. I re-built the war file and re-deployed.
6. When I re-run the application, I am right back where I was.  I get "java.lang.ClassNotFoundException:
com.mysql.jdbc.Driver".
My webapp cannot see the mysql driver jar, although it clearly sees the hibernate jar.  Hibernate
code is what is running and
attempting to load the driver.

Suggestions, gents?

David Smith wrote:
> You are right ... it shouldn't be put there.  One thing you didn't seem
> to mention is how you are using your mysql driver.   Are you trying to
> use the built-in database pooling?  If that's the case, the mysql driver
> should be in tomcat's lib directory because tomcat's internals need
> access to it as well.

I expect to use C3P0 pooling.  I have the c3p0-0.8.5.2.jar in WEB-INF/lib.  My understanding
is that Hibernate will use C3P0 if it finds the c3p0 jar in classpath.  However, I haven't
really detailed the pooling, other than setting a configuration for the pooling:
    maxActive="10" 
    maxWait="5000"
    maxIdle="4" 
I would expect to detail pooling as a later optimization once I have everything else working.

  Also can you offer some detail about your use of
> hibernate?  If it's in your webapp, it should easily see the driver jar
> file.  If it's in another webapp, it won't.
The hibernate3.jar is in WEB-INF/lib, so based on the comments by both of you the application
should see it, but it doesn't.  See below.

> 
> --David
> 
Caldarale, Charles R wrote:
>>From: Bob Marcum [mailto:bmarcum@BCScomputers.com]
>>Subject: Seeking the right solution to
>>java.lang.ClassNotFoundException: com.mysql.jdbc.Driver
>>
>>That would mean code directly in my app could see all the
>>jar files in WEB-INF/lib but hibernate code, for instance,
>>could not ?? !!
> 
> 
> Depends on where the Hibernate jar is located.  If you've put that in the webapp's WEB-INF/lib
directory, you shouldn't have a problem.
  If you've placed the Hibernate jar in some other location, you will need to put the MySQL
jar in the same place.

hibernate3.jar is in WEB-INF/lib and has always been there.

> 
> 
>>A solution I found to work is to copy the mysql-connector-java-3.1.10-
>>bin.jar file into my jseHOME/jre/lib/ext directory.
> 
> 
> Be very, very careful if you copy jars - in this case you want to move it, not copy it.
Having the same jar in multiple locations on a given branch of the classloading tree will
result in never ending errors.
If your Hibernate jar is in jre/lib/ext, then, it's likely you will have to put the MySQL
jar there.
The Hibernate jar really belongs with your webapp, not in any more global location.

I agree completely with your judgments expressed here, but that approach seems not to work,
in my case.  Why?

> 
>  - Chuck
> 
> 
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