Java下载,预览pdf文件

 @GetMapping("/previewPDF")
public void download(HttpServletRequest request, HttpServletResponse response) throws IOException {
   String filePath = "G:\\JAVA\\xxx.pdf";
   File f = new File(filePath);
   if (!f.exists()) {
       response.sendError(404, "文件资源不存在!");
       return;
   }
   BufferedInputStream br = new BufferedInputStream(new FileInputStream(f));
   byte[] bs = new byte[1024];
   int len;
   response.reset(); // 非常重要
   String fileName = "文件名称.pdf";
   String userAgent = request.getHeader("User-Agent");
   if (userAgent.contains("MSIE") || userAgent.contains("Trident")) {
       fileName = java.net.URLEncoder.encode(fileName, StandardCharsets.UTF_8.toString());
   } else {
       //非IE浏览器：
       fileName = new String(fileName.getBytes(StandardCharsets.UTF_8), StandardCharsets.ISO_8859_1);
   }
   if (false) { // 是否在线预览
       URL u = new URL("file:///" + filePath);
       String contentType = u.openConnection().getContentType();
       response.setContentType(contentType);
       response.setHeader("Content-Disposition", "inline;filename=" + fileName);
       // 文件名应该编码成utf-8，注意：使用时，我们可忽略这句
   } else {
       // 纯下载方式
       response.setContentType("application/x-msdownload");
       response.setHeader("Content-Disposition", "attachment;filename=" + fileName);
   }
   OutputStream out = response.getOutputStream();
   while ((len = br.read(bs)) > 0) {
       out.write(bs, 0, len);
   }
   out.flush();
   out.close();
   br.close();
    }