public class TestMain {
    public static void main(String[] args) throws InterruptedException {
        new Thread(new Thready()).start();
        new Thread(new Thready()).start();
        new Thread(new Thready()).start();
        new Thread(new Thready()).start();
        new Thread(new Thready()).start();
        new Thread(new Thready()).start();
        new Thread(new Thready()).start();
        new Thread(new Thready()).start();

    }

    static class Thready implements Runnable {

        @Override
        public void run() {
            try {
                Connection connection = DriverManager.getConnection("jdbc:mysql://localhost:3306/test","root","root");
                connection.setAutoCommit(false);
                connection.setTransactionIsolation(Connection.TRANSACTION_REPEATABLE_READ);
                PreparedStatement preparedStatement = connection.prepareStatement("SELECT * FROM users WHERE email =?");
                preparedStatement.setString(1,"hello");
                if (!preparedStatement.executeQuery().next()){
                    PreparedStatement preparedStatement1 = connection.prepareStatement("INSERT INTO users (email,password) values (?,?)");
                    preparedStatement1.setString(1,"hello");
                    preparedStatement1.setString(2,"pass");
                    preparedStatement1.executeUpdate();
                    preparedStatement1.close();
                }
                connection.commit();
                preparedStatement.close();
                connection.close();
            } catch (SQLException e) {
                e.printStackTrace();
            }
        }
    }