Help required in using same excel file as both Input and Output source

Question

Hello Programmers, Here I am trying to read, modify and write an excel file using JAVA, I have successfully employed Jakarta POI and read the file but the problem is that I can''t make changes in the same file and save it.
I can't use the same file for "FileInputStream" and "FileOutputStream" I think this is causing major hurdle. Any kind of suggestion and help is truly appreciated and welcome. Thank you for your time. Here I am posting my code its a bit crude please pardon.
* @(#)attempt4.java
* attempt4
* @author
* @version 1.00 2008/3/26
import java.io.*;
import java.util.*;
import org.apache.poi.poifs.filesystem.*;
import org.apache.poi.hssf.usermodel.*;
public class attempt4 {
public static void main(String[] args) {
try{
File xlFile = new File("C:\\Drifter\\Study\\Krishnan\\Test.xls");
FileInputStream readFile = new FileInputStream(xlFile);
POIFSFileSystem fileSys = new POIFSFileSystem(readFile);
HSSFWorkbook xlSheetBook = new HSSFWorkbook(fileSys);
for(int i = 0; i < xlSheetBook.getNumberOfSheets(); i++) {
HSSFSheet sheetNow = xlSheetBook.getSheetAt(i);
System.out.println("\n Now Opening Sheet Number" + (i+1));
if(sheetNow.getPhysicalNumberOfRows() > 0) {
int numOfRows = sheetNow.getLastRowNum();
int numOfColumns = 0;
for(int cols = 0; cols < numOfRows; cols++) {
HSSFRow rowNow = sheetNow.getRow(cols);
if(rowNow != null) {
if(numOfColumns < sheetNow.getRow(cols).getLastCellNum()) {
numOfColumns = sheetNow.getRow(cols).getLastCellNum();
System.out.println("\n There are " + (numOfRows+1) + " Number of Rows");
System.out.println("\n There are " + numOfColumns + " Number of Columns");
for(int j = 0; j < numOfColumns; j++) {
float colTotal = 0;
int numOfNumericCells = 0;
for(int k = 0; k < numOfRows; k++) {
HSSFRow rowReading = sheetNow.getRow(k);
if(rowReading != null) {
HSSFCell cellReading = rowReading.getCell((short)j);
if(cellReading != null) {
if(cellReading.getCellType() == 0) {
colTotal += cellReading.getNumericCellValue();
numOfNumericCells ++;
else if(cellReading.getCellType() != 0) {
cellReading.setCellValue((double) 0.00);
System.out.println(" \nSum of Column " + (j+1) + " is " + colTotal);
System.out.println(" \nAverage of Column " + (j+1) + " is " + (colTotal/numOfNumericCells));
readFile.close();
catch(FileNotFoundException ex1) {
ex1.printStackTrace();
catch(IOException ex2) {
ex2.printStackTrace();
catch(NullPointerException ex3) {
ex3.printStackTrace();
The above code can successfully read the excel document and caliculates the sum and averages of the columns, can any one please help me in writing the same into the same file in additional rows. Thank you very much for your time.

Answer 1

May be you can try to create a temporary copy of the file, do your update on it and then overwrite the original.
Edited by: jgagarin on Jun 3, 2008 6:55 PM