code: public static File ungzip(File gzip, File toDir) throws IOException {
  		toDir.mkdirs();
  		File out = new File(toDir, gzip.getName());
  		GZIPInputStream gin = null;
  		FileOutputStream fout = null;
  		try {
  			FileInputStream fin = new FileInputStream(gzip);
  			gin = new GZIPInputStream(fin);
  			fout = new FileOutputStream(out);
  			copy(gin, fout);
  			gin.close();
  			fout.close();
  		} finally {
  			closeQuietly(gin);
  			closeQuietly(fout);
  		}
  		return out;
  	}
docs: 解压gzip文件到指定的目录，目前只能解压gzip包里面只包含一个文件的压缩包。
  
  @param gzip 需要解压的gzip文件
  @param toDir 需要解压到的目录
  @return 解压后的文件
  @throws IOException