get Result from shell command on jTextArea

I have to execute a shell commande windows from java swing app and get real time result :

String cmd = jTextField1.getText();

StringBuffer output = new StringBuffer();

Process p;
try {
    p = Runtime.getRuntime().exec(cmd);

    BufferedReader reader = new BufferedReader(new InputStreamReader(p.getInputStream()));

    String line = "";
    while ((line = reader.readLine()) != null) {
        System.out.println("" + line);
        jTextArea1.append(line + "n");
    }

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

the problem is that writing in jTextArea is after execute finish not real time like System.out.println(..) .