Empty flowfile after trying to write content as Excel - groovy

Question

I have following code to read .csv and transform it to Excel:
#Grab("org.apache.poi:poi:5.0.0")
#Grab("org.apache.poi:poi-ooxml:5.0.0")
#Grab("com.opencsv:opencsv:4.6")
import java.io.*;
import org.apache.poi.ss.usermodel.*;
import org.apache.poi.xssf.usermodel.*;
import org.apache.poi.xssf.streaming.*;
import org.apache.poi.ss.SpreadsheetVersion;
import org.apache.poi.ss.util.AreaReference;
import org.apache.poi.ss.util.CellReference;
import com.opencsv.CSVReader;
def flowFile = session.get()
if(!flowFile)
return
flowFile = session.write(flowFile, { inputStream, outputStream ->
try {
SXSSFWorkbook sxssfWorkbook = new SXSSFWorkbook();
CSVReader csvReader = new CSVReader(new InputStreamReader(inputStream));
sxssfWorkbook.setCompressTempFiles(true);
SXSSFSheet sxssfSheet = sxssfWorkbook.createSheet("Sheet");
sxssfSheet.setRandomAccessWindowSize(100);
String[] strHeaders = null;
String[] dataRow = null;
int rowNum = 0;
while ((dataRow = csvReader.readNext()) != null) {
if (rowNum == 0) strHeaders = dataRow;
Row currentRow = sxssfSheet.createRow(rowNum);
for (int i = 0; i < dataRow.length; i++) {
String cellValue = dataRow[i];
currentRow.createCell(i).setCellValue(cellValue);
}
rowNum++;
}
int lastRow = rowNum -1;
int lastCol = strHeaders.length -1;
AreaReference areaReference = new AreaReference(new CellReference(0, 0), new CellReference(lastRow, lastCol), SpreadsheetVersion.EXCEL2007);
XSSFWorkbook xssfWorkbook = sxssfSheet.getWorkbook().getXSSFWorkbook();
XSSFSheet xssfSheet = xssfWorkbook.getSheet(sxssfSheet.getSheetName());
XSSFTable xssfTable = xssfSheet.createTable(areaReference);
//xssfTable.updateHeaders(); // this cannot work since xssfSheet does not contain any data until now
for (int i = 0; i < strHeaders.length; i++) {
String columnHeader = strHeaders[i];
if (xssfTable.getCTTable().getTableColumns().getTableColumnList().size() > i)
xssfTable.getCTTable().getTableColumns().getTableColumnList().get(i).setName(columnHeader);
}
xssfTable.getCTTable().addNewTableStyleInfo();
XSSFTableStyleInfo style = (XSSFTableStyleInfo)xssfTable.getStyle();
style.setName("TableStyleLight9");
style.setShowColumnStripes(false);
style.setShowRowStripes(true);
xssfTable.getCTTable().addNewAutoFilter().setRef(areaReference.formatAsString());
sxssfWorkbook.write(outputStream)
} catch (Exception ex) {
ex.printStackTrace();
}
} as StreamCallback)
session.transfer(flowFile, REL_SUCCESS)
But it returns empty flowfile after ExecuteGroovyScript.
Before I tested this in IntelliJ IDEA with Java. But reading from file and saving to file:
FileOutputStream fileout = new FileOutputStream("P:\\test.xlsx");
CSVReader csvReader = new CSVReader(new FileReader("P:\\test.csv"));
So, I guess something wrong with inputstream/outputstream?
P.S. To test some values from cell I decided to write some value to attributes:
...
sxssfWorkbook.write(outputStream);
flowFile.putAttribute('test', sxssfSheet.getRow(5).getCell(1).toString())
...
But flowfile doesn't contain this attribute.
What did I wrong?