출처 :

http://hibik.tistory.com/entry/엑셀-다운시-엑셀-파일에-암호-설정

POI 로 비밀번호로 보호된 엑셀 다운하는 jsp
POI 3.10 관련 라이브러리가 필요
MS2007 에서는 안됨 07이상에서 사용

java poi 3.15 사용했고

내용 아주 살짝 바꿈

Timestamp timestamp = new Timestamp(System.currentTimeMillis());  
response.setContentType("application/vnd.ms-excel");
response.setHeader("Content-Disposition", "attachment;filename=test_"+timestamp+".xlsx;");
response.setHeader("Content-Description", "JSP Generated Data");
     
//create a new workbook
Workbook wb = new XSSFWorkbook();

//add a new sheet to the workbook
Sheet sheet1 = wb.createSheet("Sheet1");

//add 2 row to the sheet
Row row1 = sheet1.createRow(0);
Row row2 = sheet1.createRow(1);

//create cells in the row
Cell row1col1 = row1.createCell(0);
Cell row1col2 = row1.createCell(1);

//add data to the cells
row1col1.setCellValue("Top Secret Data 1");
row1col2.setCellValue("Top Secret Data 2");

//write the excel to a file
try {
    ByteArrayOutputStream fileOut = new ByteArrayOutputStream();
    wb.write(fileOut);

    InputStream filein = new ByteArrayInputStream(fileOut.toByteArray());
    POIFSFileSystem fs = new POIFSFileSystem();
    //EncryptionInfo info = new EncryptionInfo(fs, EncryptionMode.agile);
    EncryptionInfo info = new EncryptionInfo(EncryptionMode.agile);
    Encryptor enc = info.getEncryptor();

    enc.confirmPassword("AA");


    OPCPackage opc = OPCPackage.open(filein);
    OutputStream os = enc.getDataStream(fs);
    opc.save(os);
    opc.close();
     

    OutputStream fileOut2 = null;
    //out.clear();
    //out = pageContext.pushBody();
    fileOut2 = response.getOutputStream(); 
    fs.writeFilesystem(fileOut2);
    fileOut2.close();
    fileOut.close();

}catch(Exception e){
        e.printStackTrace();
}