Tomcat 6 auth

bonjour tous le monde mon probleme avec tomcate 6 est le suivant:
-1-je veux crees une authentification via une base de donne mysql
donc j'ai cree la base que je nomee "test" suivant:
==================
CREATE TABLE users (
name VARCHAR(32),
password VARCHAR(32)
);
CREATE TABLE roles (
name VARCHAR(32),
role VARCHAR(32)
);

-2- j'ai configurer le fichier conf/context.xml de tomcate 6 comme suivant:
====================

<Context>


<WatchedResource>WEB-INF/web.xml</WatchedResource>



<Resource name="jdbc/test" type="javax.sql.DataSource" />
<ResourceParams name="jdbc/test">
<parameter>
<name>username</name>
<value>root</value>
</parameter>
<parameter>
<name>password</name>
<value>021984</value>
</parameter>
<parameter>
<name>url</name>
<value>jdbc:mysql://localhost/test</value>
</parameter>
<parameter>
<name>driverClassName</name>
<value>com.mysql.jdbc.Driver</value>
</parameter>
<parameter>
<name>maxIdle</name>
<value>2</value>
</parameter>
<parameter>
<name>maxWait</name>
<value>5000</value>
</parameter>
<parameter>
<name>maxActive</name>
<value>4</value>
</parameter>
</ResourceParams>

<Realm className="org.apache.catalina.realm.DataSourceRealm"
dataSourceName="jdbc/test"
localDataSource="true"
userTable="users"
userRoleTable="roles"
userNameCol="name"
userCredCol="password"
userRoleCol="role"
/>

</Context>

-3- mon fichier web xml est le suivant:
===================================================
<?xml version="1.0" encoding="UTF-8"?>
<web-app version="2.4" xmlns="http://java.sun.com/xml/ns/j2ee"
xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
xsi:schemaLocation="http://java.sun.com/xml/ns/j2ee
http://java.sun.com/xml/ns/j2ee/web-app_2_4.xsd">

<security-constraint>
<display-name>Test d'authentification tomcat</display-name>

<web-resource-collection>
<web-resource-name>Page sécurisée</web-resource-name>
<url-pattern>/admin/*</url-pattern>
</web-resource-collection>

<auth-constraint>
<role-name>admin</role-name>
</auth-constraint>
</security-constraint>
<login-config>

<auth-method>BASIC</auth-method>
<realm-name>Espace Membres</realm-name>
</login-config>

<security-role>
<description>Administrateur</description>
<role-name>admin</role-name>
</security-role>

<welcome-file-list>
<welcome-file>index.jsp</welcome-file>
</welcome-file-list>
</web-app>
-4- quand j'essaye d'entrer dans le repertoire priver admin , une fenetre d'authantification se lance mais quelque soit la valeur saisie ,existe ou non dans ma base "test", je peux pas entrer.
l'erreur suivant est generer par tomcate 6:
=================================
9 oct. 2007 16:51:17 org.apache.catalina.realm.DataSourceRealm open
GRAVE: Exception performing authentication
org.apache.tomcat.dbcp.dbcp.SQLNestedException: Cannot create JDBC driver of class '' for connect URL 'null'
at org.apache.tomcat.dbcp.dbcp.BasicDataSource.createDataSource(BasicDataSource.java:780)
at org.apache.tomcat.dbcp.dbcp.BasicDataSource.getConnection(BasicDataSource.java:540)
at org.apache.catalina.realm.DataSourceRealm.open(DataSourceRealm.java:403)
at org.apache.catalina.realm.DataSourceRealm.authenticate(DataSourceRealm.java:283)
at org.apache.catalina.authenticator.BasicAuthenticator.authenticate(BasicAuthenticator.java:181)
at org.apache.catalina.authenticator.AuthenticatorBase.invoke(AuthenticatorBase.java:491)
at org.apache.catalina.core.StandardHostValve.invoke(StandardHostValve.java:128)
at org.apache.catalina.valves.ErrorReportValve.invoke(ErrorReportValve.java:105)
at org.apache.catalina.core.StandardEngineValve.invoke(StandardEngineValve.java:109)
at org.apache.catalina.connector.CoyoteAdapter.service(CoyoteAdapter.java:212)
at org.apache.coyote.http11.Http11Processor.process(Http11Processor.java:844)
at org.apache.coyote.http11.Http11Protocol$Http11ConnectionHandler.process(Http11Protocol.java:634)
at org.apache.tomcat.util.net.JIoEndpoint$Worker.run(JIoEndpoint.java:445)
at java.lang.Thread.run(Thread.java:619)
Caused by: java.lang.NullPointerException
at sun.jdbc.odbc.JdbcOdbcDriver.getProtocol(JdbcOdbcDriver.java:507)
at sun.jdbc.odbc.JdbcOdbcDriver.knownURL(JdbcOdbcDriver.java:476)
at sun.jdbc.odbc.JdbcOdbcDriver.acceptsURL(JdbcOdbcDriver.java:307)
at java.sql.DriverManager.getDriver(DriverManager.java:253)
at org.apache.tomcat.dbcp.dbcp.BasicDataSource.createDataSource(BasicDataSource.java:773)
... 13 more
9 oct. 2007 16:51:26 org.apache.catalina.realm.DataSourceRealm open
GRAVE: Exception performing authentication
org.apache.tomcat.dbcp.dbcp.SQLNestedException: Cannot create JDBC driver of class '' for connect URL 'null'
at org.apache.tomcat.dbcp.dbcp.BasicDataSource.createDataSource(BasicDataSource.java:780)
at org.apache.tomcat.dbcp.dbcp.BasicDataSource.getConnection(BasicDataSource.java:540)
at org.apache.catalina.realm.DataSourceRealm.open(DataSourceRealm.java:403)
at org.apache.catalina.realm.DataSourceRealm.authenticate(DataSourceRealm.java:283)
at org.apache.catalina.authenticator.BasicAuthenticator.authenticate(BasicAuthenticator.java:181)
at org.apache.catalina.authenticator.AuthenticatorBase.invoke(AuthenticatorBase.java:491)
at org.apache.catalina.core.StandardHostValve.invoke(StandardHostValve.java:128)
at org.apache.catalina.valves.ErrorReportValve.invoke(ErrorReportValve.java:105)
at org.apache.catalina.core.StandardEngineValve.invoke(StandardEngineValve.java:109)
at org.apache.catalina.connector.CoyoteAdapter.service(CoyoteAdapter.java:212)
at org.apache.coyote.http11.Http11Processor.process(Http11Processor.java:844)
at org.apache.coyote.http11.Http11Protocol$Http11ConnectionHandler.process(Http11Protocol.java:634)
at org.apache.tomcat.util.net.JIoEndpoint$Worker.run(JIoEndpoint.java:445)
at java.lang.Thread.run(Thread.java:619)
Caused by: java.lang.NullPointerException
at sun.jdbc.odbc.JdbcOdbcDriver.getProtocol(JdbcOdbcDriver.java:507)
at sun.jdbc.odbc.JdbcOdbcDriver.knownURL(JdbcOdbcDriver.java:476)
at sun.jdbc.odbc.JdbcOdbcDriver.acceptsURL(JdbcOdbcDriver.java:307)
at java.sql.DriverManager.getDriver(DriverManager.java:253)
at org.apache.tomcat.dbcp.dbcp.BasicDataSource.createDataSource(BasicDataSource.java:773)
... 13 more