How to create a scroll bar?

Well I have a problem, I have 2 methods, one that counts the lines of a .txt file and another method that creates an array of the file lines so that I can print it in a JOptionpane.messagedialog

1st method

//metodo que devuelve el numero de lineas del archivo case 6
public int mostrarfarmacia(InputStream is) throws IOException{
    int n=0;
    InputStreamReader ir = new InputStreamReader(is);
    BufferedReader bs = new BufferedReader(ir);
    String linea = bs.readLine();
    while(linea!=null) {
        linea = bs.readLine();
        n++;
    }
    bs.close();
    return n;
}

2nd method

//metodo que imprime el archivo faramcia case 6
public void mostrarfarmacia1(InputStream is, int n) throws IOException{
    int i = 0;
    InputStreamReader ir = new InputStreamReader(is);
    BufferedReader bs = new BufferedReader(ir);
    String[] lineas = new String[n];
    String linea = bs.readLine();
    while(linea!=null) {
        lineas[i] = linea;
        linea = bs.readLine();
        i++;
    }
    bs.close();
    JOptionPane.showMessageDialog(null, lineas);
}

My problem is that when printing the array with the contents of the file, if the file is long, when printing it in the JOptionpane.showmessagedialog it prints a part and the rest prints it out of the screen, which makes it impossible to visualize it, I would like to know if there is a way to be able to visualize everything, or I would have to use other functions than the JOptionpane.showmessagedialog