Java后台Controller实现文件下载操作

代码

参数：

1.filePath:文件的绝对路径（d:\download\a.xlsx）

2.fileName(a.xlsx)

3.编码格式(GBK)

4.response、request不介绍了，从控制器传入的http对象

代码片.

//控制器
@RequestMapping(UrlConstants.BLACKLIST_TESTDOWNLOAD)
public void downLoad(String filePath, HttpServletResponse response, HttpServletRequest request) throws Exception {
    boolean is = myDownLoad("D:\\a.xlsx","a.xlsx","GBK",response,request);
    if(is)
     System.out.println("成功");
    else
    System.out.println("失败");
}
//下载方法
public boolean myDownLoad(String filePath,String fileName, String encoding, HttpServletResponse response, HttpServletRequest request){
   File f = new File(filePath);
    if (!f.exists()) {
      try {
        response.sendError(404, "File not found!");
      } catch (IOException e) {
        e.printStackTrace();
      }
      return false;
    }

    String type = fileName.substring(fileName.lastIndexOf(".") + 1);
    //判断下载类型 xlsx 或 xls 现在只实现了xlsx、xls两个类型的文件下载
    if (type.equalsIgnoreCase("xlsx") || type.equalsIgnoreCase("xls")){
      response.setContentType("application/force-download;charset=UTF-8");
      final String userAgent = request.getHeader("USER-AGENT");
      try {
        if (StringUtils.contains(userAgent, "MSIE") || StringUtils.contains(userAgent, "Edge")) {// IE浏览器
          fileName = URLEncoder.encode(fileName, "UTF8");
        } else if (StringUtils.contains(userAgent, "Mozilla")) {// google,火狐浏览器
          fileName = new String(fileName.getBytes(), "ISO8859-1");
        } else {
          fileName = URLEncoder.encode(fileName, "UTF8");// 其他浏览器
        }
        response.setHeader("Content-disposition", "attachment; filename=" + fileName);
      } catch (UnsupportedEncodingException e) {
        logger.error(e.getMessage(), e);
        return false;
      }
      InputStream in = null;
      OutputStream out = null;
      try {

        //获取要下载的文件输入流
        in = new FileInputStream(filePath);
        int len = 0;
        //创建数据缓冲区
        byte[] buffer = new byte[1024];
        //通过response对象获取outputStream流
        out = response.getOutputStream();
        //将FileInputStream流写入到buffer缓冲区
        while((len = in.read(buffer)) > 0) {
          //使用OutputStream将缓冲区的数据输出到浏览器
          out.write(buffer,0,len);
        }
        //这一步走完，将文件传入OutputStream中后，页面就会弹出下载框

      } catch (Exception e) {
        logger.error(e.getMessage(), e);
        return false;
      } finally {
        try {
          if (out != null)
            out.close();
          if(in!=null)
            in.close();
        } catch (IOException e) {
          logger.error(e.getMessage(), e);
        }
      }
      return true;
    }else {
      logger.error("不支持的下载类型！");
      return false;
    }
  }

实现效果

1.火狐浏览器效果

2.chrome效果，自动下载

补充知识：文件上传/下载的几种写法(java后端)

文件上传

1、框架已经帮你获取到文件对象File了

  public boolean uploadFileToLocale(File uploadFile,String filePath) {
    boolean ret_bl = false;
    try {
      InputStream in = new FileInputStream(uploadFile);
      ret_bl=copyFile(in,filePath);
    } catch (Exception e) {
      e.printStackTrace();
    }
    return ret_bl;
  }  

  public boolean copyFile(InputStream in,String filePath) {
    boolean ret_bl = false;
    FileOutputStream os=null;
    try {
      os = new FileOutputStream(filePath,false);
      byte[] b = new byte[8 * 1024];
      int length = 0;
      while ((length = in.read(b)) > 0) {
        os.write(b, 0, length);
      }
      os.close();
      in.close();
      ret_bl = true;
    } catch (Exception e) {
      e.printStackTrace();
    }finally{
        try {
          if(os!=null){
            os.close();
          }
          if(in!=null){
            in.close();
          }

        } catch (IOException e) {
          e.printStackTrace();
        }
    }
    return ret_bl;
  }

}

2、天了个撸，SB架构师根本就飘在天空没下来，根本就没想文件上传这一回事

public String uploadByHttp(HttpServletRequest request) throws Exception{
    String filePath=null;
    List<String> fileNames = new ArrayList<>();
    //创建一个通用的多部分解析器
    CommonsMultipartResolver multipartResolver = new CommonsMultipartResolver(request.getSession().getServletContext());
      //判断 request 是否有文件上传,即多部分请求
      if(multipartResolver.isMultipart(request)){
        //转换成多部分request
        MultipartHttpServletRequest multiRequest =multipartResolver.resolveMultipart(request);
        MultiValueMap<String,MultipartFile> multiFileMap = multiRequest.getMultiFileMap();
        List<MultipartFile> fileSet = new LinkedList<>();
        for(Entry<String, List<MultipartFile>> temp : multiFileMap.entrySet()){
          fileSet = temp.getValue();
        }
        String rootPath=System.getProperty("user.dir");
        for(MultipartFile temp : fileSet){
          filePath=rootPath+"/tem/"+temp.getOriginalFilename();
          File file = new File(filePath);
          if(!file.exists()){
            file.mkdirs();
          }
          fileNames.add(temp.getOriginalFilename());
          temp.transferTo(file);
        }
      }
  }

3、神啊，我正在撸框架，请问HttpServletRequest怎么获取！！！！

(1)在web.xml中配置一个监听

<listener>
    <listener-class>
      org.springframework.web.context.request.RequestContextListener
    </listener-class>
  </listener>

(2)HttpServletRequest request = ((ServletRequestAttributes)RequestContextHolder.getRequestAttributes()).getRequest();

文件下载（直接用链接下载的不算），这比较简单

1、本地文件下载（即文件保存在本地）

public void fileDownLoad(HttpServletRequest request,HttpServletResponse response,String fileName,String filePath) throws Exception {
    response.setCharacterEncoding("UTF-8");
    //设置ContentType字段值
    response.setContentType("text/html;charset=utf-8");
    //通知浏览器以下载的方式打开
    response.addHeader("Content-type", "appllication/octet-stream");
    response.addHeader("Content-Disposition", "attachment;filename="+fileName);
    //通知文件流读取文件
    InputStream in = request.getServletContext().getResourceAsStream(filePath);
    //获取response对象的输出流
    OutputStream out = response.getOutputStream();
    byte[] buffer = new byte[1024];
    int len;
    //循环取出流中的数据
    while((len = in.read(buffer)) != -1){
      out.write(buffer,0,len);
    }
  }

2、远程文件下载（即网上资源下载，只知道文件URI）

public static void downLoadFromUrl(String urlStr,String fileName,HttpServletResponse response){
     try {
         urlStr=urlStr.replaceAll("\\\\", "/");
        URL url = new URL(urlStr);
        HttpURLConnection conn = (HttpURLConnection)url.openConnection();
        //设置超时间为3秒
        conn.setConnectTimeout(3*1000);
        //防止屏蔽程序抓取而返回403错误
        conn.setRequestProperty("User-Agent", "Mozilla/4.0 (compatible; MSIE 5.0; Windows NT; DigExt)"); 

        //得到输入流
        InputStream inputStream = conn.getInputStream();  

        response.reset();
        response.setContentType("application/octet-stream; charset=utf-8");
     response.setHeader("Content-Disposition", "attachment; filename=" + new String(fileName.getBytes("GBK"),"ISO8859_1"));
        //获取响应报文输出流对象
        //获取response对象的输出流
       OutputStream out = response.getOutputStream();
       byte[] buffer = new byte[1024];
       int len;
       //循环取出流中的数据
       while((len = in.read(buffer)) != -1){
          out.write(buffer,0,len);
       }
    } catch (Exception e) {
      e.printStackTrace();
    }
  }

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