CONECTIONPOOL NO SQLSERVER

Não estou conseguindo montar uma ConnectionPool usando o sqlserver, segue abaixo a classe que estou montando e o erro.Caso alguém possa me ajudar, agradeço imensamente. O que devo passar como parâmetro no comando contexto.lookup ?

package jdbc;
import java.sql.Connection;
import java.sql.DriverManager;
import java.sql.SQLException;
import javax.naming.InitialContext;
import javax.naming.NamingException;
import javax.sql.DataSource;

/**
 *
 * @author Fernando
 */

public class Conexao {

    public static Connection getConnection() throws NamingException, SQLException{
        InitialContext contexto = new InitialContext();
        DataSource pool = (DataSource) contexto.lookup("java:comp/env");
        Connection con = pool.getConnection();

        //String url = "jdbc:sqlserver://localhost:1433/databaseName=loja-virtual";
        //String user = "USUARIO";
        //String pass = "USUARIO";

            try {
                con =DriverManager.getConnection("jdbc:sqlserver://localhost:1433;databaseName=loja-virtual", "USUARIO", "USUARIO");
                System.out.println("Conectado: "+con);

            } catch (SQLException e) {
                // TODO Auto-generated catch block
                e.printStackTrace();
        }


        return con;
    }
}

ERRO:

run:
Exception in thread "main" javax.naming.NoInitialContextException: Need to specify class name in environment or system property, or as an applet parameter, or in an application resource file:  java.naming.factory.initial
    at javax.naming.spi.NamingManager.getInitialContext(NamingManager.java:662)
    at javax.naming.InitialContext.getDefaultInitCtx(InitialContext.java:313)
    at javax.naming.InitialContext.getURLOrDefaultInitCtx(InitialContext.java:350)
    at javax.naming.InitialContext.lookup(InitialContext.java:417)
    at jdbc.Conexao.getConnection(Conexao.java:23)
    at jdbc.TestaConection.main(TestaConection.java:22)
Java Result: 1
CONSTRUÍDO COM SUCESSO (tempo total: 0 segundos)