如何将HtmlUnit cookie保存到文件？

    public static void main(String[] args) throws Exception {        LogFactory.getFactory().setAttribute("org.apache.commons.logging.Log", "org.apache.commons.logging.impl.NoOpLog");        File file = new File("cookie.file");        ObjectInputStream in = new ObjectInputStream(new FileInputStream(file));        Set<cookie> cookies = (Set<cookie>) in.readObject();        in.close();        WebClient wc = new WebClient();        Iterator<cookie> i = cookies.iterator();        while (i.hasNext()) { wc.getcookieManager().addcookie(i.next());        }        HtmlPage p = wc.getPage("http://google.com");        ObjectOutput out = new ObjectOutputStream(new FileOutputStream("cookie.file"));        out.writeObject(wc.getcookieManager().getcookies());        out.close();    }