java 下载文件

测试用的后端代码

        // 1.获取下载目标
        String filename = "aa.txt";
        System.out.println(filename);
        // 2.找到下载目标
        String path = getServletContext().getRealPath("download/" + filename);
        System.out.println("path:"+path);
        File file = new File(path);
        if (file.exists()) {
            // 3.如果文件存在，那么设置响应的内容为下载，告诉浏览器将信息识别成下载
            // 判断一下浏览器
            String agent = request.getHeader("User-Agent");
            if (agent.contains("Firefox")) {// 火狐
                BASE64Encoder base64Encoder = new BASE64Encoder();
                filename = "=?utf-8?B?" + base64Encoder.encode(filename.getBytes("utf-8")) + "?=";
            } else {// ie和谷歌
                filename = URLEncoder.encode(filename, "utf-8");
            }
            response.setHeader("Content-Disposition", "attachment; filename=" + filename);
            // 4.获取文件流
            FileInputStream fis = new FileInputStream(file);
            OutputStream os = response.getOutputStream();
            // 5.返回给浏览器
            int len = 0;
            byte[] buffer = new byte[1024];
            while ((len = fis.read(buffer)) != -1) {
                os.write(buffer, 0, len);
            }
            os.flush();// flush一下，确保一下
            os.close();
            fis.close();
        } else {
            response.setContentType("text/html;charset=UTF-8");
            response.getWriter().write("找不到文件");
        }

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前端如何下载文件