代码如下，已经测试：

private static void unzipFile(final String dir, final File zf)
    {
        File file = null;
        try
        {
            ZipFile zipFile = new ZipFile(zf.toString());
            Enumeration<?> entries = zipFile.entries();
            while (entries.hasMoreElements())
            {
                ZipEntry entry = (ZipEntry)entries.nextElement();

                String filename = entry.getName();

                //目录，产生后返回。
                if (entry.isDirectory())
                {
                    file = new File(dir + File.separator +filename);
                    file.mkdirs();
                    continue;
                }
                //确实有这种情况。
                else if (filename.indexOf('/') >= 0)
                {
                    String subdir = filename.substring(0, filename.lastIndexOf('/'));
                    file = new File(dir + File.separator +subdir);
                    file.mkdirs();
                }
                file = new File(dir + File.separator +filename);
                file.createNewFile();

                InputStream      is  = zipFile.getInputStream(entry);
                FileOutputStream fos = new FileOutputStream(file);
                int count = 0;
                byte buf[] = new byte[4096];
                while ((count = is.read(buf)) > 0)
                { 
                    fos.write(buf, 0, count);
                }
                fos.close();
                is.close();
            }
            zipFile.close();
        }
        catch (Exception e)
        {
            System.out.println(dir+", "+zf+", "+file);
            e.printStackTrace();
        }
    }