excel to csv sample https://stackoverflow.com/questions/18077264/convert-csv-to-xls-xlsx-using-apache-poi

ExcelToCSV.java

import org.apache.poi.ss.usermodel.Row;
import org.apache.poi.xssf.streaming.SXSSFSheet;
import org.apache.poi.xssf.streaming.SXSSFWorkbook;
import org.apache.poi.xssf.usermodel.XSSFRow;
import org.apache.poi.xssf.usermodel.XSSFSheet;
import org.apache.poi.xssf.usermodel.XSSFWorkbook;

import java.io.BufferedReader;
import java.io.FileOutputStream;
import java.io.FileReader;
import java.nio.file.Files;
import java.nio.file.Paths;
import java.util.concurrent.atomic.AtomicReference;
import java.util.stream.Stream;

public class Main {

    public static void convertCsvToXlsx(String xlsLocation, String csvLocation, String sheetName) throws Exception {
        SXSSFWorkbook workbook = new SXSSFWorkbook();
        SXSSFSheet sheet = (SXSSFSheet) workbook.createSheet(sheetName);
        AtomicReference<Integer> row = new AtomicReference<>(0);
        Files.readAllLines(Paths.get(csvLocation)).forEach(line -> {
            Row currentRow = sheet.createRow(row.getAndSet(row.get() + 1));
            String[] nextLine = line.split(",");
            Stream.iterate(0, i -> i + 1).limit(nextLine.length).forEach(i -> {
                currentRow.createCell(i).setCellValue(nextLine[i]);
            });
        });

        FileOutputStream fos = new FileOutputStream(xlsLocation);
        workbook.write(fos);
        fos.flush();
    }


    public static void csvToXLSX() {
        try {
            String csvFileAddress = "test.csv"; //csv file address
            String xlsxFileAddress = "test.xlsx"; //xlsx file address
            XSSFWorkbook workBook = new XSSFWorkbook();
            XSSFSheet sheet = workBook.createSheet("sheet1");
            String currentLine = null;
            int RowNum=0;
            BufferedReader br = new BufferedReader(new FileReader(csvFileAddress));
            while ((currentLine = br.readLine()) != null) {
                String str[] = currentLine.split(",");
                RowNum++;
                XSSFRow currentRow=sheet.createRow(RowNum);
                for(int i=0;i<str.length;i++){
                    currentRow.createCell(i).setCellValue(str[i]);
                }
            }

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

    public static void main(String[] args) throws Exception {
        csvToXLSX();
        convertCsvToXlsx("test1.xlsx", "test.csv", "test");
        convertCsvToXlsx("test1.xlsx", "test.csv", "test2");
    }
}