How to add new sheets to existing excel workbook using apache POI?

Question

I am trying to write List data into multiple excel sheet in one work book. like for first list, the code will create new workbook and create new sheet for list[1], for secon

Answer 1

To add more than one Excel sheet to a new Excel file, those sheets need to be created from one workbook, and written once to the file output stream

import java.io.*;
import java.util.*;
import org.apache.poi.ss.usermodel.*;
import org.apache.poi.xssf.usermodel.*;

public class JustATest {
   public static void main(String[] args) throws Exception  {       

        XSSFWorkbook AWorkbook = new XSSFWorkbook(); //Create blank workbook 

        for (int i = 0; i < 10; i++) {
            XSSFSheet spreadsheet = AWorkbook.createSheet(" Employee "+i);

            // the follwing code is to create dummy data in sheets 
            // is similar to the one at tutorialPoint.com
            XSSFRow row;            
            //This data needs to be written (Object[])
            Map < String, Object[] > empinfo =    new TreeMap< String, Object[] >();
            empinfo.put( "1", new Object[] { "EMP ID", "EMP NAME", "DESIGNATION" });
            for (int j = 0; j < i; j++) {
                empinfo.put( j+2+"", new Object[] {  j+2+"", "Fadel K", "Technical Manager" });                
            }          
            //Iterate over data and write to sheet
            Set keyid = empinfo.keySet();
            int rowid = 0;
            for (String key : keyid){
               row = spreadsheet.createRow(rowid++);
               Object [] objectArr = empinfo.get(key);
               int cellid = 0;
               for (Object obj : objectArr){
                  Cell cell = row.createCell(cellid++);
                  cell.setCellValue((String)obj);
               }
            }            
            // dummy data creation over.
        }       

        // here you write all sheets at once, by writing the entier workbook
        FileOutputStream out = new FileOutputStream(new File("AllData.xlsx"));
        AWorkbook.write(out);
        out.close();               
   }
}