Content Table
2017-05-22

HttpServletResponse 下载文件

实现点击按钮下载文件以及点击 a 标签下载文件，注意一下几个问题:

  • 浏览器中点击链接下载文件没啥好说的，但是点击按钮怎么实现下载呢？

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    调用 window.open(url) 就可以了

  • 服务器端需要设置响应头表明是以流的形式下载文件

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    response.setContentType("application/octet-stream");

  • 文件名有中文时需要处理乱码问题

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    String filename = new String(paper.getOriginalName().getBytes("UTF-8"), "ISO8859_1"); // 解决乱码问题
    response.setHeader("Content-Disposition", "attachment;filename=" + filename);

浏览器端

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<!DOCTYPE html>
<html>

<head>
    <meta charset="utf-8">
    <title></title>
</head>

<body>
    <a href="/download/papers/1">点击链接下载</a>
    <button onclick="download1()">点击按钮下载</button>
  	<button onclick="download2">点击按钮下载</button>

    <script>
        // 会打开一个空白页下载，然后空白页消失，用户体验不好
        function download1() {
            window.open('/download/papers/1');
        }

        // 直接下载，用户体验好
        function download2() {
            var $form = $('<form method="GET"></form>');
            $form.attr('action', '/download/papers/1');
            $form.appendTo($('body'));
            $form.submit();
        }
    </script>
</body>

</html>
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// 不使用 jQuery 下载文件的代码
var form = document.createElement('form');
form.method = 'GET';
form.action = '/download/papers/1';
document.body.appendChild(form);
form.submit();

服务器端

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@GetMapping("/download/papers/{paperId}")
public void downloadPaper(@PathVariable String paperId, HttpServletResponse response) {
    InputStream in = null;
    OutputStream out = null;

    try {
        Paper paper = paperMapper.findPaperByPaperId(paperId);
        String filename = new String(paper.getOriginalName().getBytes("UTF-8"), "ISO8859_1"); // 解决乱码问题
        // You must tell the browser the file type you are going to send
        // for example application/pdf, text/plain, text/html, image/jpg
        response.setContentType("application/octet-stream"); // 以流的形式下载文件
        response.setHeader("Content-Disposition", "attachment;filename=" + filename); // 下载保存时的文件名
        // response.setContentLength(length); // [可选] 设置文件的大小，浏览器就能够知道下载进度条了

        in = new FileInputStream(paperService.getPaperFile(paper));
        out = response.getOutputStream();
        IOUtils.copy(in, out);
    } catch (Exception ex) {
        logger.warn(ex.getMessage());
    } finally {
        IOUtils.closeQuietly(in);
        IOUtils.closeQuietly(out);
    }
}