java-tutorials/spring-mvc-java/src/main/java/com/baeldung/excel/ExcelPOIHelper.java

package com.baeldung.excel;

import org.apache.poi.ss.usermodel.Cell;
import org.apache.poi.ss.usermodel.CellType;
import org.apache.poi.ss.usermodel.CellStyle;
import org.apache.poi.ss.usermodel.IndexedColors;
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.xssf.usermodel.XSSFWorkbook;
import org.apache.poi.xssf.usermodel.XSSFFont;
import org.apache.poi.ss.usermodel.DateUtil;
import org.apache.poi.ss.usermodel.FillPatternType;
import java.io.File;
import java.io.FileOutputStream;
import java.io.FileInputStream;
import java.io.IOException;
import java.io.InputStream;
import java.util.Map;
import java.util.HashMap;
import java.util.ArrayList;
import org.springframework.stereotype.Service;

@Service
public class ExcelPOIHelper {

    public Map<Integer, ArrayList<String>> readExcel(String fileLocation) throws IOException {

        Map<Integer, ArrayList<String>> data = new HashMap<Integer, ArrayList<String>>();
        FileInputStream file = new FileInputStream(new File(fileLocation));
        Workbook workbook = new XSSFWorkbook(file);
        Sheet sheet = workbook.getSheetAt(0);
        int i = 0;
        for (Row row : sheet) {
            data.put(i, new ArrayList<String>());
            for (Cell cell : row) {
                switch (cell.getCellTypeEnum()) {
                case STRING:
                    data.get(i)
                        .add(cell.getRichStringCellValue()
                            .getString());
                    break;
                case NUMERIC:
                    if (DateUtil.isCellDateFormatted(cell)) {
                        data.get(i)
                            .add(cell.getDateCellValue() + "");
                    } else {
                        data.get(i)
                            .add(cell.getNumericCellValue() + "");
                    }
                    break;
                case BOOLEAN:
                    data.get(i)
                        .add(cell.getBooleanCellValue() + "");
                    break;
                case FORMULA:
                    data.get(i)
                        .add(cell.getCellFormula() + "");
                    break;
                default:
                    data.get(i)
                        .add(" ");
                }
            }
            i++;
        }
        if (workbook != null){
            workbook.close();
        }
        return data;
    }

    public void writeExcel() throws IOException {
        Workbook workbook = new XSSFWorkbook();

        try {
            Sheet sheet = workbook.createSheet("Persons");
            sheet.setColumnWidth(0, 6000);
            sheet.setColumnWidth(1, 4000);

            Row header = sheet.createRow(0);

            CellStyle headerStyle = workbook.createCellStyle();

            headerStyle.setFillForegroundColor(IndexedColors.LIGHT_BLUE.getIndex());
            headerStyle.setFillPattern(FillPatternType.SOLID_FOREGROUND);

            XSSFFont font = ((XSSFWorkbook) workbook).createFont();
            font.setFontName("Arial");
            font.setFontHeightInPoints((short) 16);
            font.setBold(true);
            headerStyle.setFont(font);

            Cell headerCell = header.createCell(0);
            headerCell.setCellValue("Name");
            headerCell.setCellStyle(headerStyle);

            headerCell = header.createCell(1);
            headerCell.setCellValue("Age");
            headerCell.setCellStyle(headerStyle);

            CellStyle style = workbook.createCellStyle();
            style.setWrapText(true);

            Row row = sheet.createRow(2);
            Cell cell = row.createCell(0);
            cell.setCellValue("John Smith");
            cell.setCellStyle(style);

            cell = row.createCell(1);
            cell.setCellValue(20);
            cell.setCellStyle(style);

            row = sheet.createRow(3);
            cell = row.createCell(0);
            cell.setCellValue("Ana Johnson");
            cell.setCellStyle(style);

            cell = row.createCell(1);
            cell.setCellValue(30);
            cell.setCellStyle(style);

            File currDir = new File(".");
            String path = currDir.getAbsolutePath();
            String fileLocation = path.substring(0, path.length() - 1) + "temp.xlsx";

            FileOutputStream outputStream = new FileOutputStream(fileLocation);
            workbook.write(outputStream);
        } finally {
            if (workbook != null) {
                try {
                    workbook.close();
                } catch (IOException e) {
                    e.printStackTrace();
                }
            }
        }
    }

}