On Mon, 6 Jan 2003, Michael Gerdau wrote:
> Date: Mon, 06 Jan 2003 10:21:02 +0100 > From: Michael Gerdau <[EMAIL PROTECTED]> > Reply-To: Tomcat Users List <[EMAIL PROTECTED]> > To: "[EMAIL PROTECTED]" <[EMAIL PROTECTED]> > Subject: Strange behaviour of Tomcat classloader > > Hi ! > > I've come across an IMO strange behaviour of the Tomcat classloader > and would like to ask, wether this is intended and if yes why it is > that way. > > I'm having a struts based webapp running under Tomcat 4.1.18 > The webapp makes use of a DB2 database via commons-dbcp.jar > which comes with struts. > The db2java.jar (containing the DB2 JDBC driver) has been put > into the shared/lib directory. > > So far so good. > > I recently removed from the webapps lib dir the common-*.jar files > that are made public by tomcat in the common/lib dir, among them > commons-dbcp.jar. > > After doing so Tomcat could no longer load the DB2 JDBC driver > (which are in shared/lib). After copying them to commons/lib it > once again worked. > > However when I once again copy commons-dbcp.jar into the webapps > lib dir then loading the DB2 JDBC driver from shared/lib works. > > > My understanding is, that the DB2 JDBC driver is loaded by the > webapplication. However once the commons-dbcp.jar from the common/lib > dir has been loaded and utilized then all at a sudden shared/lib > seems no longer part of the searchpath. But when commons-dbcp.jar > is taken from the webapps lib dir then shared/lib obviously still > is in the search path. > > > Is this intended ? Well, it is definitely a consequence of the way that the class loaders are architected in Tomcat. See: http://jakarta.apache.org/tomcat/tomcat-4.1-doc/class-loader-howto.html > And why ? The JDBC driver classes, ultimately, are loaded by the commons-dbcp code. So, the driver has to be visible to the class loader from which commons-dbcp is loaded, or a parent of that class loader. In the Tomcat case, the shared class loader (loads classes from shared/lib) is *below* the common class loader (loads classes from common/lib). Therefore, if you put commons-dbcp in common/lib and the driver in shared/lib, the driver classes will not be visible. > > Thank you, best, > Michael Craig -- To unsubscribe, e-mail: <mailto:[EMAIL PROTECTED]> For additional commands, e-mail: <mailto:[EMAIL PROTECTED]>
