how to return excel in Struts2 result?

InputStream excelStreamString contentDispositionString documentFormat = "xlsx"
String excel() {

    ServletContext servletContext = ServletActionContext.getServletContext()
    String filePath = servletContext.getRealPath("/WEB-INF/template/excel/mytemplate.${documentFormat}")

    File file = new File(filePath)
    Workbook wb = WorkbookFactory.create(new FileInputStream(file))

    Sheet sheet = wb.getSheetAt(0)
<write to excel file>

    ByteArrayOutputStream baos = new ByteArrayOutputStream()
    wb.write(baos)
    excelStream = new ByteArrayInputStream(baos.toByteArray())
    contentDisposition = "filename=\"myfilename.${documentFormat}\""

    return SUCCESS}
String getExcelContentType() {
    return documentFormat == "xlsx" ? "application/vnd.openxmlformats-officedocument.spreadsheetml.sheet" : "application/vnd.ms-excel"
}

in struts.xml

----------

<action name="excelAction" method="excel">
<result name="excel" type="stream">
    <param name="contentType">application/vnd.ms-excel</param>
    <param name="inputName">excelStream</param>
    <param name="contentDisposition">attachment; filename="${fileName}"</param>
    <param name="bufferSize">1024</param>
    <param name="contentLength">${contentLength}</param>
 </result>
</action>