/**

     * @方法名稱：deleteFolder

     * @方法描述：遞迴刪除目錄下的所有檔案及子目錄下所有檔案

     * @param dir 將要刪除的檔案目錄

     * @return boolean Returns "true" if all deletions were successful.

     *                 If a deletion fails, the method stops attempting to

     *                 delete and returns "false".

     * @作者日期：liurui   2017-07-15

     */

    public boolean deleteDir(File dir) {

        if (dir.isDirectory()) {

            String[] children = dir.list();

          //遞迴刪除目錄中的子目錄下

            for (int i=0; i<children.length; i++) {

                boolean success = deleteDir(new File(dir, children[i]));

                if (!success) {

                    return false;

                }

            }

        }

        // 目錄此時為空，可以刪除

        return dir.delete();

    }