Convert CSV to XLSX (Streaming)

csvToXlsx.groovy

@Grab("org.apache.poi:poi:3.16")
@Grab("org.apache.poi:poi-ooxml:3.16")
import org.apache.poi.xssf.usermodel.*;
import org.apache.poi.ss.usermodel.*;
import org.apache.poi.xssf.streaming.*;

def csvToExelNotExists() {
    try {
        String csvFileAddress = "./test.csv"; 
        String xlsxFileAddress = "./autos.xlsx";

        SXSSFWorkbook workBook = new SXSSFWorkbook();
        // Set whether temp files should be compressed.
        workBook.setCompressTempFiles(true);

        SXSSFSheet sheet = workBook.createSheet("sheet2");
        // Specifies how many rows can be accessed at most via getRow().
        sheet.setRandomAccessWindowSize(1000);

        String currentLine = null;
        int RowNum = 0;
        BufferedReader br = new BufferedReader(new FileReader(csvFileAddress));
        while ((currentLine = br.readLine()) != null) {
            String[] str = currentLine.split(",");
            Row currentRow = sheet.createRow(RowNum);
            str.eachWithIndex{col,index ->
                currentRow.createCell(index).setCellValue(str[index]);
            }                
            RowNum++;

            if (RowNum % 1000 == 0) {
                println RowNum;
            }
        }

        FileOutputStream fileOutputStream =  new FileOutputStream(xlsxFileAddress);
        workBook.write(fileOutputStream);
        fileOutputStream.close();
        System.out.println("Done");
    } catch (Exception ex) {
        ex.printStackTrace();
    }
}

def csvToExelExists() {
    try {
       String csvFileAddress = "./test.csv";  
       FileInputStream myxls = new FileInputStream("./autos.xlsx");
       XSSFWorkbook studentsSheet = new XSSFWorkbook(myxls);
       XSSFSheet worksheet = studentsSheet.getSheetAt(0);
       int lastRow=worksheet.getLastRowNum();
       System.out.println(lastRow);
       
       String currentLine = null;
       int RowNum = lastRow+1;
       BufferedReader br = new BufferedReader(new FileReader(csvFileAddress));
       br.readLine() // skip 1 line
        while ((currentLine = br.readLine()) != null) {            
            String[] str = currentLine.split(",");
            // Row row = worksheet.createRow(++lastRow); 
            Row row = worksheet.createRow(RowNum);             
            str.eachWithIndex{col,index ->
                row.createCell(index).setCellValue(str[index]);
            }           
            RowNum++;
        }
    //    Row row = worksheet.createRow(++lastRow);        
    //    row.createCell(1).setCellValue("Dr.Hola");       
       myxls.close();
       FileOutputStream output_file =new FileOutputStream(new File("./autos2.xlsx"));  
       studentsSheet.write(output_file);
       output_file.close();
       System.out.println(" is successfully written");
    }
    catch(Exception ex) {
        ex.printStackTrace();
    }
}

csvToExelExists();