我如何使用jsp servlet从服务器端将Excel文件下载到客户端

Question

我正在实现一个Web应用程序，需要将数据库数据下载到excel中。 我将所有数据检索到excel中，并保存在服务器端，但是如何将excel下载到客户端？

我已经完成了以下代码：

row = spreadsheet.createRow(p);
cell = row.createCell(1);
cell.setCellValue(m);
cell = row.createCell(2);
cell.setCellValue(emp_code);
cell = row.createCell(3);
cell.setCellValue(card_no);
// ... more code

String root = getServletContext().getRealPath("/");
File    path = new File(root + "/Downloads/ExcellFile");
f="/salary_Report.xls";
String n=path+f;
System.out.println(" File name"+f);
if (!path.exists()) {
    boolean status = path.mkdirs();
}

FileOutputStream output = new FileOutputStream(new File(path+f));
workbook.write(output);
output.close();

之后，我将如何下载该Excel文件？

Answer 1

使用通用的这样的方法创建一个ExcelService类。 此方法可以用于写入文件（这对于测试以及是否需要在服务器端存储文件很有用），也可以使用此方法稍后再写入servlet的输出流。

还要注意，每个方法负责关闭资源 ，它已经打开（和只是资源） - writeToXlsx(OutputStream)的Workbook ， writeToXlsx(String)的OutputStream 。

/**
 * Create an Excel file (as OutputStream) with your data
 * 
 * @param output The OutputStream to which the method should write. 
 *        It must be opened before!
 *        Notice that although it is an <em>output</em> of the method,
 *        it is provided as an <em>input</em> parameter.
 *        The idea is: "Give me the data, and here is the place 
 *        you should put them to."
 * @throws IOException
 */
public void writeToXlsx(OutputStream output) throws IOException {
    try (final Workbook wb = new XSSFWorkbook();) {
        final Sheet sheet = wb.createSheet(...);
        // your code here to fill the sheet
        wb.write(output);
    }
}

为了您的方便（和测试），您可以创建一个写入文件的特定方法。 但是，这不是客户端应用程序要使用的方法！

/**
 * Create an Excel file (as file) with your data.
 * 
 * @param outputFile The name of the output file.
 * @throws IOException
 */
public void writeToXlsx(String outputFile) throws IOException {
    try (OutputStream output = new FileOutputStream(new File(outputFile))) {
        writeToXlsx(output);
    }
}

您的servlet可能看起来像这样。 它使用您创建的服务。

@WebServlet("/content/data")
public class DataServlet extends HttpServlet {
    private static final long serialVersionUID = ....;

    protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
        writeHeader(response);
        writeBody(response);
    }

    private void writeBody(HttpServletResponse response) throws IOException {
        // Each servlet has the output stream which is directly 
        // streamed to the client browser as the response:
        final OutputStream output = response.getOutputStream();

        // Now your service creates the data and writes them to the 
        // output stream:
        final ExcelService service = new ExcelService();
        service.writeToXlsx(output);

        // To be sure that nothing is lost:
        output.flush();
    }

    private void writeHeader(HttpServletResponse response) {
        // Here you tell the browser that the result is not HTML, but Excel.
        // The browser uses this information to open an application
        // associated in the client operating system with this type
        // of data.
        response.setContentType("application/ms-excel");

        // The browser will pass this information to Excel
        // which will consider this as the file name
        response.setHeader("Content-Disposition", "attachment; filename=MyData.xlsx");
    }    
}