Writing data to an Excel file using Java

A guide on how to write data to an Excel file using Java, leveraging the Apache POI library for effective and simple manipulation of Excel files.

In this article, we will explore how to use the Apache POI library to write data into an Excel file using Java. Apache POI is a powerful library that allows you to work with Excel files (.xls and .xlsx) effortlessly.

import org.apache.poi.ss.usermodel.*;
import org.apache.poi.xssf.usermodel.XSSFWorkbook;

import java.io.FileOutputStream;
import java.io.IOException;

public class WriteExcelExample {
    public static void main(String[] args) {
        // Create a new workbook
        Workbook workbook = new XSSFWorkbook();
        
        // Create a new sheet
        Sheet sheet = workbook.createSheet("Information");

        // Sample data to write to the Excel file
        Object[][] data = {
            {"Name", "Age", "City"},
            {"Nguyen Van A", 23, "Hanoi"},
            {"Tran Thi B", 25, "Ho Chi Minh"},
            {"Le Van C", 21, "Da Nang"}
        };

        // Write data to the sheet
        int rowCount = 0;
        for (Object[] aData : data) {
            Row row = sheet.createRow(rowCount++);
            int columnCount = 0;

            for (Object field : aData) {
                Cell cell = row.createCell(columnCount++);
                if (field instanceof String) {
                    cell.setCellValue((String) field);
                } else if (field instanceof Integer) {
                    cell.setCellValue((Integer) field);
                }
            }
        }

        // Write the workbook to a file
        try (FileOutputStream outputStream = new FileOutputStream("output.xlsx")) {
            workbook.write(outputStream);
        } catch (IOException e) {
            e.printStackTrace();
        }

        // Close the workbook
        try {
            workbook.close();
        } catch (IOException e) {
            e.printStackTrace();
        }
    }
}

Detailed Explanation

1. import org.apache.poi.ss.usermodel.*; and import org.apache.poi.xssf.usermodel.XSSFWorkbook;: Import necessary classes from the Apache POI library to work with Excel files.
2. Workbook workbook = new XSSFWorkbook();: Creates a new workbook for an Excel (.xlsx) file.
3. Sheet sheet = workbook.createSheet("Information");: Creates a new sheet named "Information".
4. Object[][] data = {...}: Initializes sample data to be written into the Excel file.
5. The for loop: Iterates through the data and writes each value into the corresponding cell in the sheet.
6. try (FileOutputStream outputStream = new FileOutputStream("output.xlsx")): Creates a FileOutputStream to write the workbook to the "output.xlsx" file.
7. workbook.write(outputStream);: Writes the workbook's data to the Excel file.
8. workbook.close();: Closes the workbook after completing the write operation.

System Requirements

• Java 8 or later
• Library: Apache POI (version 5.0.0 or later)

How to install the libraries needed to run the Java code above

1. Download the Apache POI library from Apache POI's official website.
2. Add the necessary JAR files to your project's classpath, including:
   • poi-5.0.0.jar
   • poi-ooxml-5.0.0.jar
   • poi-ooxml-schemas-5.0.0.jar
   • And other dependency libraries.

Tips

• Always validate your input data before writing it to the Excel file.
• When using Apache POI, ensure to close the workbook after writing to avoid resource leaks.