java里http服务器如何将文件制成一个下载路径

/
  文件下载
 /
@RequestMapping("/downloadfile")
public void offLineResponseActiveFile(String resStr, HttpServletResponse response) {
    PrintWriter pw = null;
    StringBuffer sb = new StringBuffer();
    
    try {
        String fileName = "文件名";
        responsesetCharacterEncoding("UTF-8");
        responsesetContentType("application/x-msdownload");
        responseaddHeader("Cache-Control", "no-cache, no-store, must-revalidate");
        responseaddHeader("charset", "utf-8");
        responseaddHeader("Pragma", "no-cache");
        responsesetHeader("Content-Disposition", "attachment; filename=\"" + fileName + "\"; filename=utf-8''" + fileName );
        sbappend(resStr);
        pw = responsegetWriter();
        pwwrite(sbtoString());
        pwclose();
        responseflushBuffer();
    } catch (IOException e) {
        loggerinfo("下载文件出错");
        eprintStackTrace();
        if (pw != null) {
            pwclose();
        }
    } finally {
        if (pw != null) {
            pwclose();
        }
    }
}

resStr 字段传写入文件里的内容