【JavaWeb学习 | 第22篇】文件上传下载与 Excel 导入导出

<%-- upload.jsp --%>
<form action="${pageContext.request.contextPath}/upload" method="post" 
      enctype="multipart/form-data">

    选择文件：<input type="file" name="uploadFile" /><br><br>
    描述：<input type="text" name="description" /><br><br>

    <input type="submit" value="上传" />
</form>

// com.example.web.UploadServlet.java
@WebServlet("/upload")
@MultipartConfig(
    fileSizeThreshold = 1024*1024*2,      // 2MB 临时文件阈值
    maxFileSize = 1024*1024*10,           // 单个文件最大10MB
    maxRequestSize = 1024*1024*50         // 整个请求最大50MB
)
public class UploadServlet extends HttpServlet {

    private static final String UPLOAD_DIR = "uploads";   // 相对路径

    @Override
    protected void doPost(HttpServletRequest req, HttpServletResponse resp) 
            throws ServletException, IOException {

        // 获取上传目录的绝对路径（推荐放在 WEB-INF 外或自定义路径）
        String uploadPath = getServletContext().getRealPath("") + File.separator + UPLOAD_DIR;
        File uploadDir = new File(uploadPath);
        if (!uploadDir.exists()) uploadDir.mkdirs();

        try {
            // 使用 Commons FileUpload
            DiskFileItemFactory factory = new DiskFileItemFactory();
            ServletFileUpload upload = new ServletFileUpload(factory);

            // 解析请求
            List<FileItem> items = upload.parseRequest(req);

            for (FileItem item : items) {
                if (!item.isFormField()) {   // 是文件
                    String fileName = new File(item.getName()).getName();  // 防止路径穿越
                    String filePath = uploadPath + File.separator + fileName;

                    // 保存文件
                    item.write(new File(filePath));

                    req.setAttribute("message", "文件上传成功！文件名：" + fileName);
                } else {   // 是普通表单字段
                    String fieldName = item.getFieldName();
                    String value = item.getString("UTF-8");
                    System.out.println(fieldName + " = " + value);
                }
            }
        } catch (Exception e) {
            req.setAttribute("message", "上传失败：" + e.getMessage());
            e.printStackTrace();
        }

        req.getRequestDispatcher("/upload.jsp").forward(req, resp);
    }
}

@WebServlet("/download")
public class DownloadServlet extends HttpServlet {

    @Override
    protected void doGet(HttpServletRequest req, HttpServletResponse resp) 
            throws ServletException, IOException {

        String fileName = req.getParameter("filename");   // 如：测试文档.docx

        // 文件真实路径
        String filePath = getServletContext().getRealPath("") + "/uploads/" + fileName;
        File file = new File(filePath);

        if (!file.exists()) {
            resp.getWriter().write("文件不存在！");
            return;
        }

        // 设置响应头（关键！）
        resp.setContentType("application/octet-stream");
        resp.setContentLength((int) file.length());

        // 处理中文文件名乱码（通用方案）
        String userAgent = req.getHeader("User-Agent");
        String encodedFileName;
        if (userAgent.contains("Firefox")) {
            encodedFileName = "=?utf-8?B?" + 
                Base64.getEncoder().encodeToString(fileName.getBytes("utf-8")) + "?=";
        } else {
            encodedFileName = URLEncoder.encode(fileName, "UTF-8").replace("+", "%20");
        }

        resp.setHeader("Content-Disposition", 
            "attachment; filename=\"" + encodedFileName + "\"");

        // 流传输
        try (InputStream in = new FileInputStream(file);
             OutputStream out = resp.getOutputStream()) {

            byte[] buffer = new byte[4096];
            int bytesRead;
            while ((bytesRead = in.read(buffer)) != -1) {
                out.write(buffer, 0, bytesRead);
            }
            out.flush();
        }
    }
}

<a href="${pageContext.request.contextPath}/download?filename=报告.docx">下载报告</a>

// ExportExcelServlet.java
@WebServlet("/exportExcel")
public class ExportExcelServlet extends HttpServlet {

    @Override
    protected void doGet(HttpServletRequest req, HttpServletResponse resp) 
            throws ServletException, IOException {

        // 模拟数据（实际从数据库查询）
        List<User> userList = UserService.findAll();

        // 创建工作簿
        XSSFWorkbook workbook = new XSSFWorkbook();
        XSSFSheet sheet = workbook.createSheet("用户列表");

        // 创建标题行
        String[] headers = {"ID", "用户名", "年龄", "邮箱"};
        Row headerRow = sheet.createRow(0);
        for (int i = 0; i < headers.length; i++) {
            Cell cell = headerRow.createCell(i);
            cell.setCellValue(headers[i]);
        }

        // 填充数据
        int rowNum = 1;
        for (User user : userList) {
            Row row = sheet.createRow(rowNum++);
            row.createCell(0).setCellValue(user.getId());
            row.createCell(1).setCellValue(user.getUsername());
            row.createCell(2).setCellValue(user.getAge());
            row.createCell(3).setCellValue(user.getEmail());
        }

        // 设置响应头
        resp.setContentType("application/vnd.openxmlformats-officedocument.spreadsheetml.sheet");
        String fileName = "用户列表_" + new SimpleDateFormat("yyyyMMdd").format(new Date()) + ".xlsx";

        String encodedName = URLEncoder.encode(fileName, "UTF-8").replace("+", "%20");
        resp.setHeader("Content-Disposition", "attachment; filename=\"" + encodedName + "\"");

        // 输出
        workbook.write(resp.getOutputStream());
        workbook.close();
    }
}

// 在上传成功后或单独的 ImportServlet 中
XSSFWorkbook workbook = new XSSFWorkbook(new FileInputStream(excelFile));
XSSFSheet sheet = workbook.getSheetAt(0);

for (int i = 1; i <= sheet.getLastRowNum(); i++) {   // 从第2行开始（跳过标题）
    Row row = sheet.getRow(i);
    String username = row.getCell(0).getStringCellValue();
    int age = (int) row.getCell(1).getNumericCellValue();
    // ... 保存到数据库
}
workbook.close();