How Do I Read and Write to an Excel Spreadsheet With Java? - excel

Question

Summary of Problem
I have created a simple program to read from and write to a spreadsheet. But it does not work. Does anyone know what I am doing wrong?
What I Have Tried
I have successfully been able to read from a spreadsheet. I have successfully been able to write to a spreadsheet. However, I cannot do both at the same time.
It seems that the createRow function overwrites the entire row. Thus, erasing previous data. This is a pretty severe constraint. It might be what is preventing me from reading and writing at the same time.
I noticed that the output says "The supplied file was empty (zero bytes long)". But I made sure that the path is correct and that there is indeed data in the spreadsheet. Not sure where that error is coming from.
I've tried following suggestions from other posts on Stack Overflow, but none of their suggestions including closing both the fileInputStream and fileOutputStream seems to affect my program at all.
My Code
package certExamPractice;
import java.io.FileInputStream;
import java.io.FileOutputStream;
import java.io.IOException;
import java.util.HashSet;
import java.util.Set;
import org.apache.poi.xssf.usermodel.XSSFSheet;
import org.apache.poi.xssf.usermodel.XSSFWorkbook;
public class SpreadsheetPractice {
public static void main(String[] args) throws IOException {
String path = "C:/Users/james/Desktop/Spreadsheets/Spreadsheet4.xlsx";
FileInputStream fileInputStream = new FileInputStream(path);
FileOutputStream fileOutputStream = new FileOutputStream(path);
XSSFWorkbook workbook = new XSSFWorkbook(fileInputStream);
XSSFSheet sheet = workbook.createSheet("Sheet1");
Set<String> vir = new HashSet<String>();
vir.add(sheet.getRow(0).getCell(0).getStringCellValue());
vir.add(sheet.getRow(1).getCell(0).getStringCellValue());
vir.add(sheet.getRow(2).getCell(0).getStringCellValue());
vir.add(sheet.getRow(3).getCell(0).getStringCellValue());
sheet.getRow(0).createCell(1).setCellValue("zeta");
sheet.getRow(1).createCell(1).setCellValue("eta");
sheet.getRow(2).createCell(1).setCellValue("theta");
sheet.getRow(3).createCell(1).setCellValue("iota");
System.out.println("Vir = " + vir);
workbook.write(fileOutputStream);
workbook.close();
fileOutputStream.close();
}
}
My Spreadsheet
My spreadsheet.
The Output
Exception in thread "main" org.apache.poi.EmptyFileException: The supplied file was empty (zero bytes long)
at org.apache.poi.util.IOUtils.peekFirstNBytes(IOUtils.java:112)
at org.apache.poi.poifs.filesystem.FileMagic.valueOf(FileMagic.java:209)
at org.apache.poi.openxml4j.opc.internal.ZipHelper.verifyZipHeader(ZipHelper.java:143)
at org.apache.poi.openxml4j.opc.internal.ZipHelper.openZipStream(ZipHelper.java:175)
at org.apache.poi.openxml4j.opc.ZipPackage.<init>(ZipPackage.java:104)
at org.apache.poi.openxml4j.opc.OPCPackage.open(OPCPackage.java:312)
at org.apache.poi.ooxml.util.PackageHelper.open(PackageHelper.java:47)
at org.apache.poi.xssf.usermodel.XSSFWorkbook.<init>(XSSFWorkbook.java:299)
at certExamPractice.SpreadsheetPractice.main(SpreadsheetPractice.java:18)

Answer 1

The following code allows you to read from and write to a spreadsheet. You need to write the beginning code and the end code. Then you can read and write as you wish in the middle.
package certExamPractice;
import java.io.FileInputStream;
import java.io.FileOutputStream;
import java.io.IOException;
import java.io.OutputStream;
import java.util.HashSet;
import java.util.Set;
import org.apache.poi.ss.usermodel.Cell;
import org.apache.poi.ss.usermodel.Row;
import org.apache.poi.ss.usermodel.Sheet;
import org.apache.poi.ss.usermodel.Workbook;
import org.apache.poi.ss.usermodel.WorkbookFactory;
public class SpreadsheetPractice {
public static void main(String[] args) throws IOException{
//BEGINNING
String path = "C:/Users/james/Desktop/Spreadsheets/Spreadsheet4.xlsx";
FileInputStream fileInputStream = new FileInputStream(path);
Workbook workbook = WorkbookFactory.create(fileInputStream);
Sheet sheet = workbook.getSheet("Sheet1");
Row row = sheet.getRow(0);
Cell cell = row.getCell(0);
if (cell == null) { cell = row.createCell(0); }
//READ
Set<String> vir = new HashSet<String>();
vir.add(sheet.getRow(0).getCell(0).getStringCellValue());
vir.add(sheet.getRow(1).getCell(0).getStringCellValue());
vir.add(sheet.getRow(2).getCell(0).getStringCellValue());
vir.add(sheet.getRow(3).getCell(0).getStringCellValue());
System.out.println("Vir = " + vir);
//WRITE
sheet.getRow(0).createCell(1).setCellValue("zeta");
sheet.getRow(1).createCell(1).setCellValue("theta");
sheet.getRow(2).createCell(1).setCellValue("eta");
sheet.getRow(3).createCell(1).setCellValue("iota");
//END
try (OutputStream fileOutputStream = new FileOutputStream(path)) {
workbook.write(fileOutputStream);
}
workbook.close();
}
}