Apache POI - remove external Book reference - excel

Question

We receive excel files in our system and upon downloading them, i need to remove any reference to external workbook for security reasons.
i wrote the following function to remove external links as well as removing content from the cell referencing the book.
public static byte[] cleanFile(byte[] excelByteArrayworkbook) throws IOException {
ByteArrayOutputStream bos = new ByteArrayOutputStream();
try (InputStream targetStream = new ByteArrayInputStream(excelByteArrayworkbook)){
try (XSSFWorkbook workbook = new XSSFWorkbook(targetStream)) {
XSSFEvaluationWorkbook evalWorkbook = XSSFEvaluationWorkbook.create((XSSFWorkbook) workbook);
Iterator<Sheet> sheetIterator = workbook.iterator();
int i = 0;
while (sheetIterator.hasNext()) {
Sheet sheet = sheetIterator.next();
EvaluationSheet evalSheet = evalWorkbook.getSheet(i);
i++;
for (Row row : sheet) {
for (Cell cell : row) {
if (cell.getCellType() == Cell.CELL_TYPE_FORMULA) {
EvaluationCell evaluationCell = evalSheet.getCell(cell.getRowIndex(), cell.getColumnIndex());
try {
Ptg[] formulaTokens = evalWorkbook.getFormulaTokens(evaluationCell);
for (Ptg formulaToken : formulaTokens) {
int externalSheetIndex = -1;
if (formulaToken instanceof Ref3DPtg) {
Ref3DPtg refToken = (Ref3DPtg) formulaToken;
externalSheetIndex = refToken.getExternSheetIndex();
} else if (formulaToken instanceof Area3DPtg) {
Area3DPtg refToken = (Area3DPtg) formulaToken;
externalSheetIndex = refToken.getExternSheetIndex();
} else if (formulaToken instanceof Ref3DPxg) {
Ref3DPxg refToken = (Ref3DPxg) formulaToken;
externalSheetIndex = refToken.getExternalWorkbookNumber();
} else if (formulaToken instanceof Area3DPxg) {
Area3DPxg refToken = (Area3DPxg) formulaToken;
externalSheetIndex = refToken.getExternalWorkbookNumber();
}
if (externalSheetIndex >= 0) {
cell.setCellFormula(null);
}
else if (cell.getCellFormula().contains("[")) {
cell.setCellFormula(null);
}
}
} catch (Exception e) {
cell.setCellFormula(null);
}
}
}
}
}
List<ExternalLinksTable> links = workbook.getExternalLinksTable();
links.forEach(link -> {
if(link.getCTExternalLink().isSetDdeLink())
link.getCTExternalLink().unsetDdeLink();
if(link.getCTExternalLink().isSetExtLst())
link.getCTExternalLink().unsetExtLst();
if(link.getCTExternalLink().isSetOleLink())
link.getCTExternalLink().unsetOleLink();
if(link.getCTExternalLink().isSetExternalBook())
link.getCTExternalLink().unsetExternalBook();
link.getCTExternalLink().setNil();
});
try {
workbook.write(bos);
} finally {
bos.close();
}
}
}
try {
bos.close();
} catch (IOException e) {
}
return bos.toByteArray();
}
However, the file i am getting is not valid. Excel prompt me with an error message saying
Excel error message
The version of Apache POI i am using is 3.13 . I can't find an example where i can remove external links

Answer 1

I found the answer. The code was not removing references in the Name Manager area.
I have added the following in my function
List<XSSFName> nameUsingExternalBook = new ArrayList<XSSFName>();
for (int j = 0; j < workbook.getNumberOfNames(); j++) {
XSSFName name= workbook.getNameAt(j);
if(name.getRefersToFormula() != null && name.getRefersToFormula().contains("[")) {
nameUsingExternalBook.add(name);
}
}
nameUsingExternalBook.forEach(name->{
workbook.removeName(name.getNameName());
});
So the new excel file is wellformed