Oracle UCP sql exception Cannot get Connection to Datasource

Question

I am trying to integrate UCP and tomcat and i have made the configuration correct as given in the oracle docs but still something is missing and while connecting I am getting the following exception

java.sql.SQLException: Unable to start the Universal Connection Pool: oracle.ucp
.UniversalConnectionPoolException: Cannot get Connection from Datasource

I have all jar files in my lib folder and context.xml defined but still need to know where I am going wrong or something i am missing following is the code which is throwing exception

pds=PoolDataSourceFactory.getPoolDataSource();

     // Setting connection parameters
     pds.setConnectionFactoryClassName("oracle.jdbc.pool.OracleDataSource");

     pds.setURL("jdbc:oracle:thin:@//localhost:1521:xe");
     pds.setUser("hr");
     pds.setPassword("hr"); // till here working fine 

     // setting pool properties 
     pds.setInitialPoolSize(5);  // throws above mentioned Exception 
     pds.setMinPoolSize(5);
     pds.setMaxPoolSize(15);
     System.out.println("Creating pool /// debug 4");
     System.out.println("Creating pool .... finish");