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From "Dag H. Wanvik (JIRA)" <j...@apache.org>
Subject [jira] Commented: (DERBY-4944) Embedded Derby does not start when derby.jar is dynamically uploaded / added to the classpath
Date Tue, 14 Dec 2010 17:03:03 GMT

    [ https://issues.apache.org/jira/browse/DERBY-4944?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12971312#action_12971312

Dag H. Wanvik commented on DERBY-4944:

Thanks for tracking this down and the fix, Michael! It looks good to me. 

I'll commit it after running our regression suite and back-port it to the 10.7 branch, so
it would be included in an update release of 10.7 if there will be one (likely). The initial
release of 10.7 is going out the door as we speak, so it will not make it there, unfortunately.

> Embedded Derby does not start when derby.jar is dynamically uploaded / added to the classpath
> ---------------------------------------------------------------------------------------------
>                 Key: DERBY-4944
>                 URL: https://issues.apache.org/jira/browse/DERBY-4944
>             Project: Derby
>          Issue Type: Bug
>          Components: Store
>    Affects Versions:
>         Environment: various windows versions, jdk1.6.0 and 1.5.0
>            Reporter: Michael Dobrovnik
>            Priority: Minor
>         Attachments: BDFF.diff
> Hi, 
> For our workflow-system, we can use a variety of DBMS as the store engine. Derby is one
of them especially popular
> for test and development purposes. During setup of our system, we allow to upload a jar
file with the JDBC-Driver for the DBMS.
> In case of derby, we use the embedded mode and upload derby.jar. After that we add the
jar to the repositories of our class loader
> and call 
> Class drc = Class.forName("org.apache.derby.jdbc.EmbeddedDriver", true, ourclassloader);
> Driver drv = (Driver)drc.newInstance();
> this worked perfectly for many years up to version, but ceased to work in;

> i assume the unreleased future versions are affected, too
> when derby.jar is placed in the classpath manually before starting our setup, everything
works fine regardless of the derby version.
> investigations lead to the following conclusion:
> - since rev. 982370 this is broken, in the immediate predecessor rev. 980035  it worked.
> - rev. 982370 in  the org.apache.derby.impl.store.raw.data.BaseDataFileFactory class
introduced a new method
>     private static String jarClassPath(final Class cls) which tries to find the jarfile
from which derby was loaded.
>   it contains the following lines: 
> if ( cs == null )
>   return null;
> URL result = cs.getLocation();
> return result.toString();        
>   but in the case, when we dynamically load derby, 
>   cs is not null but cs.getLocation() is null. so i propose to change the line with the
if to:
> ...
> if ( cs == null || cs.getLocation()==null)
>   return null;
> ...
> or maybe it would be better to surround the whole body of the method with a try catch,
since it is not essential, and a null 
> return value is also ok?
> thank you for your efforts concerning derby at large, 
> Michael

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