public class Singleton {

private static Singleton INSTANCE = null;

private Connection connection;

public Singleton()
{

}

public static Singleton getInstance()
{
    if(INSTANCE == null)
    {
        INSTANCE = new Singleton();
    }

    return INSTANCE;
}

public void setSingletonConnexion(String URL, String userName, String password, String networkAlias) throws SQLException, ClassNotFoundException
{
    Class.forName("oracle.jdbc.driver.OracleDriver");

    System.setProperty("pathOfTNS");

    //System.out.println("driver ok");

    this.connection = DriverManager.getConnection("jdbc:oracle:thin:@"+URL+":PORT:SID", userName,password);

    System.out.println("CO OK");

    ResultSet rs = this.connection.createStatement().executeQuery("SELECT * FROM TABLE");

    if(rs.next())
    {
        System.out.println(rs.getString(5));
    }
}

public Connection getConnection()
{
    return this.connection;
}