直接上代码：Ａｃｔｉｏｎ中代码片段。

@RequestMapping("download")
public String download(ModelMap model, @ModelAttribute("e") Template t, HttpServletResponse response, HttpServletRequest request) throws Exception {
   Account acc = getLoginAccount();　　　
   if(acc==null || StringUtils.isBlank(acc.getAccount())){
      return ("/account/login");
   }

String fileUrl = template.getFileUrl();　　　／／ｕｒｌ　路径，　如　http://×××××/×××/××××/image/20170525/中文.jpg
String  filename = fileUrl.substring(fileUrl.lastIndexOf("/")+1);　　／／截取最后的文件名　　－＞　中文．ｊｐｇ
filename = processFileName( request,  filename);
BufferedOutputStream bf = null;
try {
   response.setHeader("Content-disposition", "attachment; filename = " + filename);
   bf = new BufferedOutputStream(response.getOutputStream());
   bf.write(this.httpConverBytes(fileUrl,request));
｝．．．．


重要的　ｐｒｏｃｅｓｓＦｉｌｅＮａｍｅ方法。

public static String processFileName(HttpServletRequest request, String fileNames) {
   String codedfilename = null;
   try {
      String agent = request.getHeader("USER-AGENT");
      if (null != agent && -1 != agent.indexOf("MSIE") || null != agent
            && -1 != agent.indexOf("Trident")) {// ie
         String name = java.net.URLEncoder.encode(fileNames, "UTF8");
         codedfilename = name;
      } else if (null != agent && -1 != agent.indexOf("Mozilla")) {// 火狐,chrome等
         codedfilename = new String(fileNames.getBytes("UTF-8"), "iso-8859-1");
      }
   } catch (Exception e) {
      e.printStackTrace();
   }
   return codedfilename;
}

／／ｈｔｔｐＣｏｎｖｅｒＢｙｔｅｓ　方法

public static byte[] httpConverBytes(String path,HttpServletRequest request) {
   BufferedInputStream in = null;
   ByteArrayOutputStream out = null;
   URLConnection conn = null;
   int httpResult=0;
   try {
      StringBuffer sb = new StringBuffer();
      for(int i=0;i<path.length();i++){
         char a=path.charAt(i);　　　／／ｕｒｌ路径的中文部分重新编码　很重要
         if(a>127){//将中文UTF-8编码
            sb.append(URLEncoder.encode(String.valueOf(a), "utf-8"));
         }else{
            sb.append(String.valueOf(a));
         }
      }
      URL url = new URL(sb.toString()); //创建URL
      URLConnection urlconn = url.openConnection(); // 试图连接并取得返回状态码urlconn.connect(); 
      HttpURLConnection httpconn = (HttpURLConnection) urlconn;
      httpResult = httpconn.getResponseCode();
      in = new BufferedInputStream(httpconn.getInputStream());

      if (httpResult != HttpURLConnection.HTTP_OK){  //不等于HTTP_OK说明连接不成功
         System.out.print("连接失败！");
      }else {
         out = new ByteArrayOutputStream(1024);
         byte[] temp = new byte[1024];
         int size = 0;
         while ((size = in.read(temp)) != -1) {
            out.write(temp, 0, size);
         }
         byte[] content = out.toByteArray();
         return content;
      }
   } catch (Exception e) {
      e.printStackTrace();
   }
   finally {
      try {
         in.close();
      } catch (IOException e) {
         e.printStackTrace();
      }
      try {
         out.close();
      } catch (IOException e) {
         e.printStackTrace();
      }
   }
   return null;
}


通过以上处理下划线问题解决了。

springmvc文件下载之文件名下划线问题终极解决方案