求帮忙看错

public void exportExcel(HttpServletRequest request,
HttpServletResponse response) {
try {
String fname = "test";// Excel文件名
OutputStream os = response.getOutputStream();
response.setHeader("Content-disposition", "attachment; filename="+ fname + ".xls"); 
response.setContentType("application/msexcel");
HSSFWorkbook wb = new HSSFWorkbook();
    HSSFSheet sheet = wb.createSheet("new sheet");
    wb.setSheetName(0,"话费详单",HSSFWorkbook.ENCODING_UTF_16); //具体含义展位秦楚       
    HSSFRow row=sheet.createRow((short)0);      
    sheet.createFreezePane(0,1); 
    cteateCell(wb,row,(short)0,"手机号码");        
    cteateCell(wb,row,(short)1,"呼叫类型");       
    cteateCell(wb,row,(short)2,"对方号码");        
    cteateCell(wb,row,(short)3,"起始时间");       
    cteateCell(wb,row,(short)4,"通话时间");        
    cteateCell(wb,row,(short)5,"通话地点");      
    cteateCell(wb,row,(short)6,"长途类型");    
    cteateCell(wb,row,(short)7,"基本话费");    
    cteateCell(wb,row,(short)8,"长话费");     
    cteateCell(wb,row,(short)9,"总话费");
    wb.write(os);      
os.flush();     
os.close();
} catch (IOException e) {
// TODO Auto-generated catch block
e.printStackTrace();
}// 取得输出流 


}

private void cteateCell(HSSFWorkbook wb,HSSFRow row,short col,String val){   
HSSFCell cell=row.createCell(col);       
cell.setEncoding(HSSFCell.ENCODING_UTF_16);        
cell.setCellValue(val);     
HSSFCellStyle cellstyle=wb.createCellStyle();    
cellstyle.setAlignment(HSSFCellStyle.ALIGN_CENTER_SELECTION); 
cell.setCellStyle(cellstyle);
}
这代码导不出excel啊