LZ想法很好。我来帮你实现：
首先通过压缩方式：

    /***************************************************************************
     * 压缩文件
     * 
     * @author Louis
     * @param srcfile
     *            需要压缩的文件列表
     * @param zipfile
     *            压缩后的文件
     * @author Louis
     */
    public static void ZipFiles(java.io.File[] srcfile, java.io.File zipfile) {
        byte[] buf = new byte[1024];
        try {
            // Create the ZIP file
            ZipOutputStream out = new ZipOutputStream(new FileOutputStream(
                    zipfile));
            // Compress the files
            for (int i = 0; i < srcfile.length; i++) {
                FileInputStream in = new FileInputStream(srcfile[i]);
                // Add ZIP entry to output stream.
                out.putNextEntry(new ZipEntry(srcfile[i].getName()));
                // Transfer bytes from the file to the ZIP file
                int len;
                while ((len = in.read(buf)) > 0) {
                    out.write(buf, 0, len);
                }
                // Complete the entry
                out.closeEntry();
                in.close();
            }
            // Complete the ZIP file
            out.close();

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

    /***************************************************************************
     * 解压缩文件
     * 
     * @author Louis
     * @param zipfile
     *            需要解压缩的文件
     * @param descDir
     *            解压后的文件目录
     * @author Louis
     */
    public static void UnZipFiles(java.io.File zipfile, String descDir) {
        try {
            // Open the ZIP file
            ZipFile zf = new ZipFile(zipfile);
            for (Enumeration entries = zf.entries(); entries.hasMoreElements();) {
                // Get the entry name
                ZipEntry entry = ((ZipEntry) entries.nextElement());
                String zipEntryName = entry.getName();
                InputStream in = zf.getInputStream(entry);
                // System.out.println(zipEntryName);
                OutputStream out = new FileOutputStream(descDir + zipEntryName);
                byte[] buf1 = new byte[1024];
                int len;
                while ((len = in.read(buf1)) > 0) {
                    out.write(buf1, 0, len);
                }
                // Close the file and stream
                in.close();
                out.close();
            }
        } catch (IOException e) {
            e.printStackTrace();
        }
    }

    /**
     * 下载服务器中的txt文件
     * @param filePath    
     *             需要下载的文件File包装类
     * @param filename
     *             下载后默认的文件名
     * @param response
     * 
     * @throws Exception
     */
    public static void download(File filePath, String filename, HttpServletResponse response) throws Exception{
        // TODO Auto-generated method stub
        BufferedInputStream bis = null;
        BufferedOutputStream bos = null;
        OutputStream fos = null;
        InputStream fis = null;

        //File uploadFile = new File(filePath);
         File uploadFile = filePath;
        fis = new FileInputStream(uploadFile);
        bis = new BufferedInputStream(fis);
        fos = response.getOutputStream();
        bos = new BufferedOutputStream(fos);
        filename = URLEncoder.encode(filename, "GBK");
        
        //弹出下载对话框的关键代码
        response.setContentType("application/x-download");
        response.setHeader("Content-Disposition","attachment;filename="+ filename);
        int bytesRead = 0;
        //都是用输入流进行先读，然后用输出流去写，用的是缓冲输入输出流
        byte[] buffer = new byte[8192];
        while ((bytesRead = bis.read(buffer, 0, 8192)) != -1)  {
            try{
                bos.write(buffer, 0, bytesRead);
            }catch(Exception e){}
        }
        try{bos.flush();}catch(Exception e){} 
        try{bos.close();}catch(Exception e){}
        try{bis.close();}catch(Exception e){}
        try{fos.close();}catch(Exception e){}
        try{fis.close();}catch(Exception e){}
    }

    /**
     * 上传文件并返回上传后的文件名
     * 
     * @param uploadFileName
     *            被上传的文件名称
     * @param savePath
     *            文件的保存路径
     * @param uploadFile
     *            被上传的文件
     * @return 成功与否
     * @throws IOException
     */
    public static String uploadForName(String uploadFileName, String savePath, File uploadFile) throws IOException {
        String newFileName = checkFileName(uploadFileName, savePath);
        FileOutputStream fos = null;
        FileInputStream fis = null;
        try {
            fos = new FileOutputStream(savePath +"/"+ newFileName);
            fis = new FileInputStream(uploadFile);
            byte[] buffer = new byte[1024];
            int len = 0;
            while ((len = fis.read(buffer)) > 0) {
                fos.write(buffer, 0, len);
            }
        } catch (FileNotFoundException e) {
            throw e;
        } catch (IOException e) {
            throw e;
        } finally {
            try {
                if (fos != null) {
                    fos.close();
                }
                if (fis != null) {
                    fis.close();
                }
            } catch (IOException e) {
                throw e;
            }
        }
        return newFileName;
    }
******************************************************************************
上面的类只需要LZ根据逻辑组合一下。就能实现文件夹压缩或者解压缩上传下载了。。。

关于下载文件夹的问题。。我能想到的就只能是通过 写一个bat文件。然后通过java程序来调用实现。。