There appears to be an issue when attempting to use a JNDI datasource when 
defining a ROOT context. 
 
So with the simple server.xml: 
 
<Server port="8005" shutdown="SHUTDOWN"> 
 
  <GlobalNamingResources> 
    <Resource name="UserDatabase" auth="Container" 
              type="org.apache.catalina.UserDatabase" 
       description="User database that can be updated and saved" 
           factory="org.apache.catalina.users.MemoryUserDatabaseFactory" 
          pathname="conf/tomcat-users.xml" /> 
  </GlobalNamingResources> 
 
  <Service name="Catalina"> 
    <!-- HTTP connector --> 
    <Connector port="8080" 
               maxThreads="150" minSpareThreads="25" maxSpareThreads="75" 
               enableLookups="false" redirectPort="8443" acceptCount="100" 
               connectionTimeout="20000" disableUploadTimeout="true" 
               compression="on" compressionMinSize="2048"  
               noCompressionUserAgents="gozilla, traviata"  
               compressableMimeType="text/html,text/xml" /> 
 
    <!-- HTTPS connector --> 
    <Connector port="8443"  
               maxThreads="150" minSpareThreads="25" maxSpareThreads="75" 
               enableLookups="false" disableUploadTimeout="true" 
               acceptCount="100" scheme="https" secure="true" 
               clientAuth="false" sslProtocol="TLS" /> 
 
    <!-- AJP 1.3 connector (needed?) --> 
    <Connector port="8009"  
               enableLookups="false" redirectPort="8443" protocol="AJP/1.3" /> 
    <Engine name="Catalina" defaultHost="localhost"> 
      <Realm className="org.apache.catalina.realm.UserDatabaseRealm" 
             resourceName="UserDatabase"/> 
 
      <Host name='localhost' appBase='webapps' 
            unpackWARs='false' autoDeploy='true' 
            deployOnStartup='true' 
            xmlValidation='false' xmlNamespaceAware='false'> 
        <Context path='/' docBase='ROOT.war' 
                 crossContext='true'> 
          <Resource name='jdbc/myDB' auth='Container' 
                    type='javax.sql.DataSource' 
                    driverClassName='org.postgresql.Driver' 
                    url='jdbc:postgresql://localhost:5432/myDB' 
                    username='db-user' password='db-passwd' /> 
        </Context> 
      </Host> 
    </Engine> 
  </Service> 
</Server> 
 
When you do: 
 
Context ctx = new InitialContext(); 
DataSource ds = (DataSource) ctx.lookup("java:comp/env/jdbc/myDB"); 
Connection conn = ds.getConnection(); 
 
The following error gets throw: 
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) 
 
 
If you move the resource definition to <GlobalNamingResources> and do a 
resource link you get the same error.  
 
But if you change any of the following, it works fine: 
- Move the resource definition (or link if defined globally) to 
$CATALINA_HOME/conf/context.xml and remove it from the context entry in 
server.xml 
- Move the context defintion out of server.xml completely to 
$CATALINA_HOME/conf/Catalina/localhost/ROOT.xml 
- Move the context defintion out of server.xml completely to 
<webapp>/META-INF/context.xml 
- Keep the context entry and resource definition in server.xml but change the 
context path to something besides '/' 
 
This indicates that web applications mounted on the root context are treated 
differently from other web applications. I think it should be consistent.