Use java to download files on the browser

```java
public HttpServletResponse downLoad(String path, String file_name, HttpServletResponse response) {
        try {
            // path是指欲下载的文件的路径。
            //判断是否为tomcat路径下文件
            if (path.startsWith(Globals.APP_BASE_NAME)) {
                String[] paths = path.split(Globals.APP_BASE_NAME);
                path = paths[1];
                path = Mvcs.getServletContext().getRealPath(path);
            }
            File file = new File(path);
            // 取得文件名。
            String filename = "\"" + file_name + "\"";
            // 取得文件的后缀名。
            String ext = filename.substring(filename.lastIndexOf(".") + 1).toUpperCase();

            // 以流的形式下载文件。
            InputStream fis = new BufferedInputStream(new FileInputStream(path));
            byte[] buffer = new byte[fis.available()];
            fis.read(buffer);
            fis.close();
            // 清空response
            response.reset();
            // 设置response的Header
            response.addHeader("Content-Disposition", "attachment;filename=" + new String(filename.getBytes("GB2312"), "iso8859-1"));
            response.addHeader("Content-Length", "" + file.length());
            OutputStream toClient = new BufferedOutputStream(response.getOutputStream());
            response.setContentType("application/octet-stream");
            toClient.write(buffer);
            toClient.flush();
            toClient.close();
        } catch (IOException ex) {
            ex.printStackTrace();
        }
        return response;
    }