ora-29532 error when calling java source

Good Morning,
     we are having a problem running the call below:

+++++++++++++++++++++++++++++++++++
CREATE  OR REPLACE  
    AND COMPILE   JAVA SOURCE NAMED "CONCIERGE".""  RESOLVER ((*
    CONCIERGE)(* PUBLIC)) AS import java.util.Hashtable;

import javax.naming.*;

import javax.naming.directory.*;

public class doLookup{

    public  static int domname(String hostName) throws NamingException {

          Hashtable env = new Hashtable();

          env.put("java.naming.factory.initial",

                      "com.sun.jndi.dns.DnsContextFactory");

          DirContext ictx = new InitialDirContext (env );

          Attributes attrs = ictx.getAttributes (hostName, new String[] { "MX" });

          Attribute attr = attrs.get( "MX" );

          if (attr == null) return (0); else return (attr.size() );

    }

};

+++++++++++++++++++++++++++++++++++

we are getting the following error:
+++++++++++++++++++++++++++++++++++
Connecting to the database TPMCDB.

ORA-29532: Java call terminated by uncaught Java exception:

 javax.naming.NoInitialContextException: Cannot instantiate class:

 com.sun.jndi.dns.DnsContextFactory [Root exception is java.lang.ClassNotFoundException: com.sun.jndi.dns.DnsContextFactory]

ORA-06512: at "CONCIERGE.DOLOOKUP", line 1

ORA-06512: at line 7

Process exited.
+++++++++++++++++++++++++++++++++++++++++


Disconnecting from the database TPMCDB.