org.hibernate.DuplicateMappingException and tomcat

There are probably many reasons why you might get a DuplicateMappingException from an application using hibernate. Not least because you have a mapping defined twice.

However I have just found this reason and it is new to me.

In the tomcat logs I found this:

Caused by: org.hibernate.DuplicateMappingException: Duplicate class/entity mapping uk.co.formfill.dfcommon.domain.dfwv.Action
at org.hibernate.cfg.Mappings.addClass(Mappings.java:118)
at org.hibernate.cfg.HbmBinder.bindRoot(HbmBinder.java:154)
at org.hibernate.cfg.Configuration.add(Configuration.java:386)
at org.hibernate.cfg.Configuration.addInputStream(Configuration.java:427)
at org.hibernate.cfg.Configuration.addFile(Configuration.java:267)

Looking further up the tomcat logs to just before the first Exception stack trace there was this:

17-03-2009 10:44:22 [Thread-1] INFO  - Reading mappings from file: D:\apache-tomcat-6.0.14\work\Catalina\localhost\dfweb\loader\uk\co\formfill\dfcommon\hibernate\mappings\dfwv\actions.hbm.xml
17-03-2009 10:44:22 [Thread-1] INFO  - duplicate import: uk.co.formfill.dfcommon.domain.dfwv.Action->uk.co.formfill.dfcommon.domain.dfwv.Action
17-03-2009 10:44:22 [Thread-1] INFO  - duplicate import: uk.co.formfill.dfcommon.domain.dfwv.Action->Action
17-03-2009 10:44:22 [Thread-1] INFO  - Mapping class: uk.co.formfill.dfcommon.domain.dfwv.Action -> ACTIONS

So I looked in D:\apache-tomcat-6.0.14\work\Catalina\localhost\dfweb and that was empty. Strange.

The same war worked fine on a different installation and the cause was in the tomcat configuration.

The offending line was in tomcat's context.xml with the problem being the overriding of the antiJARLocking property which had been done beacuse of some historical apps..

<Context antiJARLocking="true">

Removing this and all is fine. Looking at the tomcat documentation I can not see why this problem might occurr but hey ho, it is fixed.