Getting Cannot create JDBC driver of class '' for connect URL 'null in spring tomcat application [duplicate]

I am getting the following exception while getting datasource through jndi:

Caused by: org.springframework.jdbc.CannotGetJdbcConnectionException:
     Could not get JDBC Connection; nested exception is
     org.apache.tomcat.dbcp.dbcp.SQLNestedException: Cannot create JDBC driver of class '' for connect URL 'null

Tomcat's server.xml :

     <Resource name="jdbc/testdb" auth="Container" type="javax.sql.DataSource"
          username="test" password="test1234"
          url="*********"
          driverClass="oracle.jdbc.driver.OracleDriver"
          initialSize="5" maxWait="5000"
          maxActive="120" maxIdle="5"
          validationQuery="select 1"
          poolPreparedStatements="true"/>    

Tomcat's Context.xml :

<ResourceLink name="jdbc/testdb" global="jdbc/testdb"
type="javax.sql.DataSource" />     

Spring's servlet xml :

<jee:jndi-lookup id="dataSource" jndi-name="jdbc/testdb"  resource-ref="true" />

and final Web.xml :

   <resource-ref>
       <description>Resource reference to database</description>
       <res-ref-name>jdbc/testdb</res-ref-name>
       <res-type>javax.sql.DataSource</res-type>
       <res-auth>Container</res-auth>
       <res-sharing-scope>Shareable</res-sharing-scope>
</resource-ref>

Could somebody please help me?

Error Stack trace :

  Error querying database.  Cause: org.springframework.jdbc.CannotGetJdbcConnectionException: Could not get JDBC Connection; nested exception is org.apache.tomcat.dbcp.dbcp.SQLNestedException: Cannot create JDBC driver of class '' for connect URL 'null'