如何从HSSFWorkbook对象获取输入流

Question

我希望我的web应用程序用户以Excel文件的形式下载一些数据。

我有下一个函数在response对象中发送一个输入流。

public static void sendFile(InputStream is, HttpServletResponse response) throws IOException {
        BufferedInputStream in = null;
        try {
            int count;
            byte[] buffer = new byte[BUFFER_SIZE];
            in = new BufferedInputStream(is);
            ServletOutputStream out = response.getOutputStream();
            while(-1 != (count = in.read(buffer)))
                out.write(buffer, 0, count);
            out.flush();            
        }   catch (IOException ioe) { 
            System.err.println("IOException in Download::sendFile"); 
            ioe.printStackTrace();
        } finally {
            if (in != null) {
                try { in.close(); 
                } catch (IOException ioe) { ioe.printStackTrace(); }
            }   
        }
    }

我想将我的HSSFWorkbook对象转换为输入流，并将其传递给前面的方法。

public InputStream generateApplicationsExcel() {
    HSSFWorkbook wb = new HSSFWorkbook();
    // Populate the excel object
    return null; // TODO. return the wb as InputStream 
}

http://poi.apache.org/apidocs/org/apache/poi/hssf/usermodel/HSSFWorkbook.html

Answer 1

你问题的问题是你把OutputStreams和InputStreams混在一起了。InputStream是您读取的内容，而OutputStream是您写入的内容。

这就是我将POI对象写入输出流的方式。

// this part is important to let the browser know what you're sending
response.setContentType("application/vnd.ms-excel");
// the next two lines make the report a downloadable file;
// leave this out if you want IE to show the file in the browser window
String fileName = "Blah_Report.xls";
response.setHeader("Content-Disposition", "attachment; filename=" + fileName); 

// get the workbook from wherever
HSSFWorkbook wb = getWorkbook();
OutputStream out = response.getOutputStream();
try {
   wb.write(out);
}       
catch (IOException ioe) { 
  // if this happens there is probably no way to report the error to the user
  if (!response.isCommited()) {
    response.setContentType("text/html");
    // show response text now
  }
}

如果您希望重用现有代码，则必须将POI数据存储在某个位置，然后将其转换为输入流。只需将其写入ByteArrayOutputStream，然后使用ByteArrayInputStream读取这些字节，就可以很容易地做到这一点，但我不建议这样做。您现有的方法作为通用管道实现会更有用，您可以通过管道将数据从InputStream传递到OutputStream，但不需要它来编写POI对象。

Answer 2

您可以从对象创建InputStream。

public InputStream generateApplicationsExcel() {
    HSSFWorkbook wb = new HSSFWorkbook();
    // Populate a InputStream from the excel object
    return new ByteArrayInputStream(excelFile.getBytes());
}

Answer 3

我的解决方案是首先将HSSFWorkbook传输到ByteArrayOutputStream，然后从ByteArrayOutputStream创建一个InputStream：

        HSSFWorkbook wb = ...

        // Fill an empty output stream
        ByteArrayOutputStream baos = new ByteArrayOutputStream();
        wb.write(baos);

        // Close the document
        wb.close();

        // Create the input stream (do not forget to close the inputStream after use)
        InputStream is = new ByteArrayInputStream(baos.toByteArray());