Applet: Java downloads single-page HTML (resources can be downloaded and referenced)

This program can download the reference CSS/JS and images that the page depends on. Currently, this function does not include the function of downloading HTML pages. The Code is as follows:

/* ***************************************************************************** * This software is under the Apache License Version 2.0 * Author: Tao -  mail:cn.java.river@gmail.com * Spreading Your Heart **************************************************************************** */package atao.util.html;import java.io.BufferedReader;import java.io.BufferedWriter;import java.io.File;import java.io.FileOutputStream;import java.io.FileWriter;import java.io.InputStream;import java.io.InputStreamReader;import java.net.URL;import org.apache.commons.lang.StringUtils;/** *  * A Simple HTML downloader which can also download Page resources. * 
 * Note: This Tool won't download related or sub HTML *  * @author Tao * @since 1.0 */public class HtmlDownloader{    //URL will be downloaded.    private static String url = "http://pervasive2.morselli.unimo.it/~nicola/courses/IngegneriaDelSoftware/java/J6d_xml.html";        //workspace folder.    private static String workspace = "download";        //sub css and js resources sign     private static String urlSign = "
 Note: don't use Java Character Writers,     * otherwise you can't get pictures correctly.     *      * @param subUrl     */    private static void downloadChild (String subUrl)    {        if (StringUtils.isNotEmpty (subUrl))        {            if (subUrl.startsWith ("http:"))            {                System.out.println ("subUrl not support yet.");            }            else            {                long start = System.nanoTime ();                try                {                    String forUrl = subUrl.replace (" ", "%20");                    if (!forUrl.startsWith ("/"))                    {                        forUrl = "/" + forUrl;                    }                    URL u = new URL (rootUrl + forUrl);                    InputStream reader = u.openStream ();                    File f = createDownloadFile (subUrl);                    FileOutputStream writer = new FileOutputStream (f);                    byte[] buff = new byte[1024];                    int size = -1;                    while ((size = reader.read (buff)) != -1)                    {                        writer.write (buff, 0, size);                    }                    reader.close ();                    writer.close ();                }                catch (Exception e)                {                    e.printStackTrace ();                }                System.out.println ("Source:" + subUrl +"download time(s):" + String.format ("%.3f", (double)(System.nanoTime () - start)/ 1000000000.00));            }        }        else        {            System.out.println ("subUrl is Empty.");        }    }    /**     * create sub file,create parent folders if necessary.     *      * @param url related path of a url source.     * @return created file.     */    private static File createDownloadFile (String url)    {        File f = new File (workspace, url);        f.getParentFile ().mkdirs ();        return f;    }}