Generate xlsx file with POI in a zip

Question

I export data in an xlsx files with the POI Api and added they're in a Zip file. When I open the zip I do not have any xlsx files but three directories (docProps, xl and _rels) and 1 file [Content_Types] xml. I think it's the xlsx file's description, but I don't understand why.

Code :

public InputStream exportXlsx(List<MyObject> listeOfObject) throws IOException {

        ByteArrayOutputStream excelOutputStreamZip = new ByteArrayOutputStream();
        ZipOutputStream zip = new ZipOutputStream(excelOutputStreamZip);

        for (MyObject myObject : listeOfObject) {

            XSSFWorkbook wb = new XSSFWorkbook();
            XSSFSheet wsheet = wb.createSheet("mySheet");
            XSSFRow row = wsheet.createRow(0);
            XSSFCell cell = row.createCell(1);
            cell.setCellValue(myObject.getValue1());

            // Create all sheet and cell....

            // Write WB conntent in outputStream
            wb.write(excelOutputStreamZip);

            addEntry(zip, myObject.getFileName(), excelOutputStreamZip);
        }

        InputStream inputStreamZipByte = new ByteArrayInputStream(
                ((ByteArrayOutputStream) excelOutputStreamZip).toByteArray());
        zip.close();

        return inputStreamZipByte;

    }

    public void addEntry(OutputStream zip, String filename, ByteArrayOutputStream os) {

        byte[] bytes = os.toByteArray();

        ZipEntry entry = new ZipEntry(filename);
        Date d = new Date();
        entry.setTime(d.getTime());
        try {
            ((ZipOutputStream) zip).putNextEntry(entry);
            ((ZipOutputStream) zip).write(bytes);
            ((ZipOutputStream) zip).closeEntry();
        } catch (IOException e) {
            log.error("Can't read the file !", e);
        } catch (ClassCastException cce) {
            log.error("Bad format !", cce);
        }

    }

This code is write in a service which is inject in a Struts2 action.

struts.xml :

<action name="*MyAction" class="com.omb.view.action.myAction" method="{1}">
    <result name="export" type="stream">
        <param name="contentType">application/zip</param>
        <param name="inputName">inputStreamZipByte</param>
        <param name="contentDisposition">attachment;filename="myZip.zip"</param> 
        <param name="bufferSize">1024</param>
    </result>
</action>

Answer 1

I found a part of my solution, but now I have another problem :

the problem for the inital post was in the handling of streams. Because I used the same outputStream for the Zip and the Workbook. Solution was created a new ByteArrayOutpuStream for each workbook.

// Write WB conntent in outputStream    
ByteArrayOutputStream wbOutputStream = new ByteArrayOutputStream();  
wb.write(wbOutputStream);    
addEntry(zip, myObject.getFileName(), wbOutputStream);    
wbOutputStream.close();

But...now the Zip file generated is corrupted...