SQL JDBC Tomcat "Native Library sqljdbc_auth.dll already loaded in another classloader"

Question

Using Microsoft's JDBC drivers to connect to a MS SQL database from Java running under Tomcat 6 with Windows Integration Authentication.

It works once, but from then until Tomcat is restarted I get a exception with the following root cause:

java.lang.UnsatisfiedLinkError: Native Library C:\******\tomcat\lib\sqljdbc_auth.dll already loaded in another classloader

where "******" indicates tomcats install directory.

Both sqljdbc_auth.dll and the driver Java library sqljdbc4.jar are in Tomcat's lib directory and neither are packaged with the web applications in question.

I am making no explicit calls to load or loadLibrary, it is all being handled by sqljdbc4.jar classes.

I understand that the native library (DLL) can only be loaded into the JVM once, hence the error, but I after looking around the net I still have no solution.

 

Any advice would be great. Thanks.

 

Answer 1

This issue is not specific to MS JDBC driver. This is a result of how class loading works in a JVM.

It appears that this issue can be resolved by somehow creating a separate class loader for a given application server experiencing the issue and associate the shared library. 

TomCat provides several class loaders and one of them is inteded for sharing across all web apps.

http://tomcat.apache.org/tomcat-6.0-doc/class-loader-howto.html (does not talk about this special class loader)

** Refer to http://wiki.apache.org/tomcat/HowTo for an idea on how this can be done for TomCat 6.**

 

Answer 2

See if this might help.

Copy the SQL Server JDBC driver "sqljdbc4.jar" or the SQL Server JDBC driver that you are using to the ${TOMCAT_HOME}/lib directory.