Java文件下载（excel）

最简单的方法就是把文件链接写到a标签的href里，但是有人说了，这样会暴露服务器的文件路径，有风险- -

下面整理介绍几种通过代码实现的方法：
1，

    @RequestMapping("download") 
    public ResponseEntity<byte[]> download(HttpServletRequest request) throws Exception {
        String fileName = request.getParameter("fileName");
        String path = request.getSession().getServletContext().getRealPath("")+File.separator+"WEB-INF"+File.separator+"download";
        File file = new File(path,fileName);
        HttpHeaders headers = new HttpHeaders();  
        headers.setContentType(MediaType.APPLICATION_OCTET_STREAM);  
        headers.setContentDispositionFormData("attachment", fileName);  
        return new ResponseEntity<byte[]>(FileUtils.readFileToByteArray(file),headers, HttpStatus.CREATED);  
    }  

spring里的方法，跟response无关。

2，
web.xml中

<servlet-mapping>
        <servlet-name>DownloadServlet</servlet-name>
        <url-pattern>/files/*</url-pattern>
</servlet-mapping>

    public void fileOutputStream(HttpServletRequest req, HttpServletResponse resp){
        String filepath = req.getRequestURI();
        int index = filepath.indexOf(Global.USERFILES_BASE_URL);
        if(index >= 0) {
            filepath = filepath.substring(index + Global.USERFILES_BASE_URL.length());
        }
        try {
            filepath = UriUtils.decode(filepath, "UTF-8");
        } catch (UnsupportedEncodingException e1) {
            logger.error(String.format("解释文件路径失败，URL地址为%s", filepath), e1);
        }
        File file = new File(Global.getUserfilesBaseDir() + Global.USERFILES_BASE_URL + filepath);
        try {
            FileCopyUtils.copy(new FileInputStream(file), resp.getOutputStream());
            resp.setHeader("Content-Type", "application/octet-stream");
            return;
        } catch (FileNotFoundException e) {
            req.setAttribute("exception", new FileNotFoundException("请求的文件不存在"));
            req.getRequestDispatcher("/WEB-INF/views/error/404.jsp").forward(req, resp);
        }
    }

这个方法是通过servlet拦截url请求，如果匹配到相应的路径，则下载。

3，

@RequestMapping("/exportExcel")
    public void exportExcel(HttpServletRequest request,HttpServletResponse response) {
        try {
                String filepath = ;//已存在的文件路径
                FileInputStream fis = null;
                OutputStream os = null;
                try {
                    String downLoadName = new String("导出.xls".getBytes("gbk"), "iso8859-1");
                    fis = new FileInputStream(filepath);
                    os = response.getOutputStream();// 取得输出流
                    response.reset();// 清空输出流
                    response.setHeader("Content-disposition",
                            "attachment; filename=" + downLoadName);// 设定输出文件头
                    response.setContentType("application/x-download;charset=GBK;");
                    byte[] mybyte = new byte[fis.available()];
                    int len = 0;
                    while ((len = fis.read(mybyte)) != -1) {
                        os.write(mybyte, 0, len);
                    }
                    os.close();
                } catch (IOException e) {
                    e.printStackTrace();
                }
        } catch (Exception e) {
            e.printStackTrace();
        }
    }

这个方法其实和法2类似，都是写到response中，只不过法2用FileCopyUtils.copy()简化了操作。

记住：下载之前得确定路径正确且路径下确实存在文件哦。