读写excel

import org.apache.poi.hssf.usermodel.*;
import org.apache.poi.ss.usermodel.*;
import org.apache.poi.util.IOUtils;

import java.io.ByteArrayOutputStream;
import java.io.File;
import java.lang.reflect.Field;
import java.text.DecimalFormat;
import java.text.SimpleDateFormat;
import java.util.*;

public class ExcelUtil {

    public static <T> void read(String path, Class<T> tClass,int headNum) {
        File xlsx = new File(path);
        try (Workbook workbook = WorkbookFactory.create(xlsx)) {
            Sheet sheet = workbook.getSheetAt(0);
            int rowNum = sheet.getPhysicalNumberOfRows();
            Row headRow = sheet.getRow(headNum);
            short cellNum = headRow.getLastCellNum();
            String[] titles = new String[cellNum];
            for (int j = 0; j < cellNum; j++) {
                Cell cell = headRow.getCell(j);
                titles[j] = cell.getStringCellValue();
            }

            List<T> pojoList = new ArrayList<>(rowNum - 1);


            for (int startIndex = headNum + 1; startIndex < rowNum; startIndex++) {
                Map<String, Object> valMap = new HashMap<>();
                Row row = sheet.getRow(startIndex);
                short lastCellNum = row.getLastCellNum();
                for (int j = 0; j < lastCellNum; j++) {
                    Cell cell = row.getCell(j);

                    valMap.put(titles[j], getCellValue(cell));
                }
                T t = mapToPojo(valMap, tClass);
                pojoList.add(t);
            }
            System.out.println();
        } catch (Exception e) {
            throw new RuntimeException(e);
        }


    }

    private static <T> T mapToPojo(Map<String, Object> valMap, Class<T> clazz) {
        Field[] fields = clazz.getDeclaredFields();
        T instance = null;
        try {
            instance = clazz.newInstance();
        } catch (InstantiationException e) {
            e.printStackTrace();
        } catch (IllegalAccessException e) {
            throw new RuntimeException(e);
        }
        for (Field field : fields) {
            String name = field.getName();
            field.setAccessible(true);
            try {
                field.set(instance, valMap.get(name));
            } catch (IllegalAccessException e) {
                throw new RuntimeException(e);
            }
        }

        return instance;
    }


    private static String getCellValue(Cell cell){
        CellType cellTypeEnum = cell.getCellTypeEnum();
        if (cellTypeEnum == CellType.BOOLEAN) {
            return String.valueOf(cell.getBooleanCellValue());
        } else if (cell.getCellTypeEnum() == CellType.NUMERIC) {
            String cellValue = "";
            if (HSSFDateUtil.isCellDateFormatted(cell)) {    //判断是日期类型
                CellStyle cellStyle = cell.getCellStyle();
                SimpleDateFormat dateformat = new SimpleDateFormat(cellStyle.getDataFormatString().replace("\\",""));
                Date dt = HSSFDateUtil.getJavaDate(cell.getNumericCellValue());//获取成DATE类型
                cellValue = dateformat.format(dt);
            }else{
                DecimalFormat df = new DecimalFormat("0");
                cellValue = df.format(cell.getNumericCellValue());
            }
            return cellValue;
        } else {
            return String.valueOf(cell.getStringCellValue());
        }
    }
    public static byte[] export(String sheetTitle, String[] title, List<Object> list) {

        HSSFWorkbook wb = new HSSFWorkbook();//创建excel表
        HSSFSheet sheet = wb.createSheet(sheetTitle);
        sheet.setDefaultColumnWidth(20);//设置默认行宽

        //表头样式（加粗，水平居中，垂直居中）
        HSSFCellStyle cellStyle = wb.createCellStyle();
        cellStyle.setAlignment(HorizontalAlignment.CENTER);//水平居中
        cellStyle.setVerticalAlignment(VerticalAlignment.CENTER);// 垂直居中
        //设置边框样式
        cellStyle.setBorderBottom(BorderStyle.THIN); //下边框
        cellStyle.setBorderBottom(BorderStyle.THIN); //下边框
        cellStyle.setBorderLeft(BorderStyle.THIN);//左边框
        cellStyle.setBorderTop(BorderStyle.THIN);//上边框
        cellStyle.setBorderRight(BorderStyle.THIN);//右边框

        HSSFFont fontStyle = wb.createFont();
        cellStyle.setFont(fontStyle);

        //标题样式（加粗，垂直居中）
        HSSFCellStyle cellStyle2 = wb.createCellStyle();
        cellStyle.setVerticalAlignment(VerticalAlignment.CENTER);// 垂直居中
        cellStyle2.setFont(fontStyle);

        //设置边框样式
        cellStyle2.setBorderBottom(BorderStyle.THIN); //下边框
        cellStyle2.setBorderLeft(BorderStyle.THIN);//左边框
        cellStyle2.setBorderTop(BorderStyle.THIN);//上边框
        cellStyle2.setBorderRight(BorderStyle.THIN);//右边框

        //字段样式（垂直居中）
        HSSFCellStyle cellStyle3 = wb.createCellStyle();
        cellStyle.setVerticalAlignment(VerticalAlignment.CENTER);// 垂直居中

        //设置边框样式
        cellStyle3.setBorderBottom(BorderStyle.THIN); //下边框
        cellStyle3.setBorderLeft(BorderStyle.THIN);//左边框
        cellStyle3.setBorderTop(BorderStyle.THIN);//上边框
        cellStyle3.setBorderRight(BorderStyle.THIN);//右边框

        //创建表头
        HSSFRow row = sheet.createRow(0);
        row.setHeightInPoints(20);//行高

        HSSFCell cell = row.createCell(0);
        cell.setCellValue(sheetTitle);
        cell.setCellStyle(cellStyle);

        //创建标题
        HSSFRow rowTitle = sheet.createRow(0);
        rowTitle.setHeightInPoints(20);

        HSSFCell hc;
        for (int i = 0; i < title.length; i++) {
            hc = rowTitle.createCell(i);
            hc.setCellValue(title[i]);
            hc.setCellStyle(cellStyle2);
        }
        byte result[] = null;
        ByteArrayOutputStream out = null;
        try {
            //创建表格数据
            Field[] fields;
            int i = 1;
            for (Object obj : list) {
                fields = obj.getClass().getDeclaredFields();
                HSSFRow rowBody = sheet.createRow(i);
                rowBody.setHeightInPoints(20);
                int j = 0;
                // 显示的列是你所要封装的实体类的每个对象，而且顺序是你创建对象的顺序
                for (Field f : fields) {
                    f.setAccessible(true);
                    hc = rowBody.createCell(j);
                    if (f.get(obj) != null) {
                        hc.setCellValue(f.get(obj).toString());
                    } else {
                        hc.setCellValue("");
                    }
                    hc.setCellStyle(cellStyle3);
                    j++;
                }
                i++;
            }
            out = new ByteArrayOutputStream();
            wb.write(out);
            result = out.toByteArray();
        } catch (Exception ex) {
            throw new RuntimeException("报表导出异常" + ex.getMessage());
        } finally {
            IOUtils.closeQuietly(out);
        }
        return result;
    }


}