public class Conexion {
private static Conexion instancia=null;
private static Connection conn;

private Conexion()
{
    String host="127.0.0.1:3306";
    String user="root";
    String pass="xxxx";
    String dtbs="bd_alumnos";

    try
    {
       Class.forName("com.mysql.jdbc.Driver"); //Inicializar el driver
       String newConnectionURL = "jdbc:mysql://"+host+"/"+dtbs
                    + "?" +"user=" + user + "&password=" + pass;
      conn = DriverManager.getConnection(newConnectionURL);
    }catch(Exception e)
    {
        e.printStackTrace();
    }
}

public static Conexion getInstancia()
{
    if(instancia==null) instancia=new Conexion();
    return instancia;
}

String newConnectionURL = "jdbc:mysql://"+host+"/"+dtbs
                + "?" +"user=" + user + "&password=" + pass;

if(instancia==null) instancia=new Conexion();

public class Conexion {
private static Conexion instancia=null;
private static Connection conn;

private Conexion()
{
    String host="127.0.0.1:3306";
    String user="root";
    String pass="xxxx";
    String dtbs="bd_alumnos";
    String driver = "com.mysql.jdbc.Driver";
    String connection = "jdbc:mysql://"+host+"/"+dtbs;

    try
    {
        Class.forName(driver);
        Connection conn = DriverManager.getConnection(connection, user, pass);

    }catch(Exception e)
    {
        e.printStackTrace();
    }
}

    public static Conexion getInstancia()
    {
        if(instancia==null) instancia=new Conexion();
        return instancia;
    }