private static final String USUARIO = "root";
private static final String SENHA = "123456";
private static final String URL = "jdbc:mysql://127.0.0.1:3306/aulas";
private static final String DRIVER = "com.mysql.jdbc.Driver";

public static Connection abrir() throws Exception
{
    Class.forName(DRIVER);

    Connection conn = DriverManager.getConnection(URL, USUARIO, SENHA);

    System.out.println("Conectado");

    return conn;
}

java.lang.ClassNotFoundException: com.mysql.jdbc.Driver
at java.net.URLClassLoader.findClass(Unknown Source)
at java.lang.ClassLoader.loadClass(Unknown Source)
at sun.misc.Launcher$AppClassLoader.loadClass(Unknown Source)
at java.lang.ClassLoader.loadClass(Unknown Source)
at java.lang.Class.forName0(Native Method)
at java.lang.Class.forName(Unknown Source)
at Default.Main.abrir(Main.java:52)
at Default.Main.<init>(Main.java:64)
at Default.Main.main(Main.java:36)