一、引言

        作者最近的平台项目需要生成excel，excel的导入导出是常用的功能，但是作者想做成动态的，不要固定模板，那就看看怎么实现。

二、后端

        先捋一下原理，前后端的交互看起来是制定好的接口，其实根本上是数据键值对的映射，后端可以直接用Map进行接收，只不过接收回来的数据如果是对象嵌套对象或者集合嵌套，那么就要用object接收之后再解析。

        而对于excel的导入导出来说，基本上都是转字符串再去填入文件，也不会有什么嵌套，所以可以直接用Map接收。

1、pom

        先引入工具包

                org.apache.poi
                poi-ooxml
                3.17
                
                    
                        org.apache.xmlbeans
                        xmlbeans
                    
                
            

2、导入

        导入按功能不同，步骤也不一样，如果是为了业务处理，那就是把excel数据解析之后处理完，前端再去查

        作者这边是解析完excel之后把数据直接给前端，一个意思，主要是解析excel

        首先要把excel给下载下来

@Service
public class ExcelWDownloadUtil {
    private static final LoggerService LOG = LoggerServiceFactory.getLoggerService(FileWsHelper.class);
    private static final String TITLE = "ExcelWDownloadUtil";
    /**
     * Function - 下载文件
     *
     * @param fileUrl 文件路径
     * @return 文件内容
     */
    public byte[] downloadBytes(String fileUrl) {
        HttpGet httpGet = new HttpGet(fileUrl);
        return HttpClientHelper.getInstance().getBytes(httpGet);
    }
    /**
     * excel文件后缀
     */
    private static final String EXCEL_FIX = "xlsx";
    private static final String EXCEL_FIX_OLD = "xls";
    /**
     * 文件后缀分隔符
     */
    private final static String FILE_SPLIT = ".";
    public List> downloadExcel(String excelDownloadUrl) {
        // 1. 通过http下载文件，并转为bytes
        byte[] fileBytes = downloadBytes(excelDownloadUrl);
        // 2. 将byte数组转为流
        ByteArrayInputStream byteInputStream = new ByteArrayInputStream(fileBytes);
        // 3. 将流转为excel工作薄
        String fileType = getFileType(excelDownloadUrl);
        if (StringUtilsExt.equals(fileType, EXCEL_FIX)) {
            return convertXlsxExcel(byteInputStream);
        } else if (StringUtilsExt.equals(fileType, EXCEL_FIX_OLD)) {
            return convertXlsExcel(byteInputStream);
        }
        LOG.error(TITLE, "file is not excel");
        return null;
    }
    public List> convertXlsxExcel(ByteArrayInputStream byteInputStream) {
        List> res = new ArrayList<>();
        XSSFWorkbook sheets = null;
        try {
            // 1. 转为工作薄
            sheets = new XSSFWorkbook(byteInputStream);
            // 2. 取第一个Sheet
            XSSFSheet sheet = sheets.getSheetAt(0);
            // 3. 循环行列，转为String返回
            DataFormatter formatter = new DataFormatter();
            for (int i = 0; i <= sheet.getLastRowNum(); i++) {
                List rowString = getStringFormRow(sheet.getRow(i), formatter);
                if (CollectionUtilsExt.isNotBlank(rowString)) {
                    res.add(rowString);
                }
            }
        } catch (IOException e) {
            LOG.error(TITLE, e);
            throw new FileExecuteException("excel file io exception");
        } finally {
            // 关闭文件流
            if (sheets != null) {
                try {
                    sheets.close();
                } catch (IOException e) {
                    LOG.error(TITLE, e);
                }
            }
        }
        return res;
    }
    public List> convertXlsExcel(ByteArrayInputStream byteInputStream) {
        List> res = new ArrayList<>();
        HSSFWorkbook sheets = null;
        try {
            // 1. 转为工作薄
            sheets = new HSSFWorkbook(byteInputStream);
            // 2. 取第一个Sheet
            HSSFSheet sheet = sheets.getSheetAt(0);
            // 3. 循环行列，转为String返回
            DataFormatter formatter = new DataFormatter();
            for (int i = 0; i < sheet.getLastRowNum(); i++) {
                List rowString = getStringFormRow(sheet.getRow(i), formatter);
                if (CollectionUtilsExt.isNotBlank(rowString)) {
                    res.add(rowString);
                }
            }
        } catch (IOException e) {
            LOG.error(TITLE, e);
            throw new FileExecuteException("excel file io exception");
        } finally {
            // 关闭文件流
            if (sheets != null) {
                try {
                    sheets.close();
                } catch (IOException e) {
                    LOG.error(TITLE, e);
                }
            }
        }
        return res;
    }
    private List getStringFormRow(Row row, DataFormatter formatter) {
        if (Objects.isNull(row)) {
            return null;
        }
        List rowString = new ArrayList<>();
        for (int j = 0; j < row.getLastCellNum(); j++) {
            rowString.add(getStringFromCell(row.getCell(j), formatter));
        }
        return rowString;
    }
    private String getStringFromCell(Cell cell, DataFormatter formatter) {
        if (Objects.isNull(cell)) {
            return null;
        }
        if (CellType.NUMERIC == cell.getCellTypeEnum()) {
            BigDecimal num = BigDecimal.valueOf(cell.getNumericCellValue());
            // 判断是否有小数，防止1变成了1.0，下游会报错
            if (new BigDecimal(num.intValue()).compareTo(num) == 0) {
                return String.valueOf(num.intValue());
            }
            // 这里是防止出现科学计数法
            return NumberToTextConverter.toText(cell.getNumericCellValue());
        } else {
            return formatter.formatCellValue(cell);
        }
    }
    public static String getFileType(String fileName) {
        if (StringUtilsExt.isBlank(fileName) || !fileName.contains(FILE_SPLIT)) {
            return null;
        }
        return fileName.substring(fileName.lastIndexOf(FILE_SPLIT) + 1);
    }
}

        解析成键值对，说白了解析excel得到的List>，第一行是列名作为键，下面行数据都作为值

if (CollectionUtilsExt.isBlank(fileList) || fileList.size() <= 1) {
            throw new OrderException("EXCEL_NO_DATA");
        }
        List> res = new ArrayList<>();
        List cellName = fileList.get(0);
        for (int i = 1; i < fileList.size(); i++) {
            List row = fileList.get(i);
            Map rowMap = new HashMap<>();
            for (int j = 0; j < row.size(); j++) {
                rowMap.put(cellName.get(j), row.get(j));
            }
            res.add(rowMap);
        }
        return res;

3、导出

        导出的话就是把数据生成excel，第一把前端传的数据或者数据库查出来的数据生成excel，第二步把excel上传内部服务器，第三步把生成文件的地址给前端打开

        生成excel

@Service
public class GenerateExcelUtil {
    private static final int SHEET_ROW = 1000;
    private static final short FONT_SIZE = 11;
    private int getCellWidth(String cellName) {
        // 根据列名获取配置的列宽度，不配置也行，默认宽度
        Map cellWidthMap = Config.getMap(CELL_WIDTH_MAP);
        if (cellWidthMap == null || !cellWidthMap.containsKey(cellName)) {
            return 4000;
        }
        return Integer.parseInt(cellWidthMap.get(cellName));
    }
    private short getCellColor(String cellName) {
        // 根据列名获取配置的列颜色，不配置也行，默认颜色
        Map cellColorMap = Config.getMap(CELL_COLOR_MAP);
        if (cellColorMap == null || !cellColorMap.containsKey(cellName)) {
            return 0;
        }
        return Short.parseShort(cellColorMap.get(cellName));
    }
    public SXSSFWorkbook generateExcel(String sheetName, List> excelBoList,
        List cellNameList) {
        // 生成excel文件
        SXSSFWorkbook workbook = new SXSSFWorkbook(SHEET_ROW);
        // 建表
        SXSSFSheet sheet = workbook.createSheet(sheetName);
        // 设置每列宽度
        for (int i = 0; i < cellNameList.size(); i++) {
            sheet.setColumnWidth(i, getCellWidth(cellNameList.get(i)));
        }
        // 构建表头
        SXSSFRow rowHead = sheet.createRow(0);
        for (int i = 0; i < cellNameList.size(); i++) {
            createCell(rowHead, i, cellNameList.get(i), createTitleStyle(workbook, getCellColor(cellNameList.get(i))));
        }
        // 构建内容
        CellStyle contentStyle = createContentStyle(workbook);
        for (int i = 0; i < excelBoList.size(); i++) {
            Map excelBo = excelBoList.get(i);
            createRow(sheet, i + 1, excelBo, contentStyle, cellNameList);
        }
        return workbook;
    }
    private CellStyle createTitleStyle(SXSSFWorkbook workbook, short color) {
        Font boldFont = workbook.createFont();
        boldFont.setFontHeightInPoints(FONT_SIZE);
        boldFont.setBold(true);
        boldFont.setColor(color);
        CellStyle style = workbook.createCellStyle();
        style.setFont(boldFont);
        style.setWrapText(true);
        style.setAlignment(HorizontalAlignment.CENTER);
        style.setVerticalAlignment(VerticalAlignment.CENTER);
        style.setBorderBottom(BorderStyle.THIN);
        style.setBorderLeft(BorderStyle.THIN);
        style.setBorderRight(BorderStyle.THIN);
        style.setBorderTop(BorderStyle.THIN);
        return style;
    }
    private CellStyle createContentStyle(SXSSFWorkbook workbook) {
        Font boldFont = workbook.createFont();
        boldFont.setFontHeightInPoints(FONT_SIZE);
        CellStyle style = workbook.createCellStyle();
        style.setFont(boldFont);
        style.setWrapText(true);
        style.setAlignment(HorizontalAlignment.CENTER);
        style.setVerticalAlignment(VerticalAlignment.CENTER);
        return style;
    }
    private void createCell(SXSSFRow row, int column, Object value, CellStyle style) {
        SXSSFCell cell = row.createCell(column);
        cell.setCellType(CellType.STRING);
        cell.setCellValue(Null.or(value, Object::toString, null));
        cell.setCellStyle(style);
    }
    private void createRow(SXSSFSheet sheet, int rowIndex, Map map, CellStyle style,
        List cellName) {
        SXSSFRow row = sheet.createRow(rowIndex);
        for (int i = 0; i < cellName.size(); i++) {
            createCell(row, i, map.get(cellName.get(i)), style);
        }
    }
}

        上传服务器 

@Service
public class ExcelUploadUtil {
    private static final LoggerService LOG = LoggerServiceFactory.getLoggerService(ExcelUploadUtil.class);
    private static final String TITLE = "ExcelUploadUtil";
    /**
     * 上传文件的地址
     */
    private static final String UPLOAD_URL = "fileUploadUrl";
    /**
     * 上传文件的contentType
     */
    private static final String EXCEL_CONTENT_TYPE =
        "application/vnd.openxmlformats-officedocument.spreadsheetml.sheet";
    /**
     * 创建文件的后缀
     */
    public static final String FILE_SUFFIX = ".xlsx";
    /**
     * 请求头
     */
    private static final String CONTENT_TYPE = "Content-Type";
    public FileResponseBo uploadExcel(SXSSFWorkbook workbook, String filePrefix) {
        File file = convertFile(workbook, filePrefix);
        LOG.info(TITLE, "convertFile");
        if (file == null) {
            return null;
        }
        return uploadFile(file, EXCEL_CONTENT_TYPE);
    }
    private File convertFile(SXSSFWorkbook workbook, String filePrefix) {
        File file = null;
        FileOutputStream fos = null;
        try {
            file = File.createTempFile(filePrefix, FILE_SUFFIX);
            fos = new FileOutputStream(file);
            workbook.write(fos);
        } catch (IOException e) {
            // 这里上传文件有io异常无需处理，后续返回空，会对空处理
            LOG.error(TITLE, e);
        } finally {
            // 关闭文件流
            if (fos != null) {
                try {
                    fos.close();
                } catch (IOException e) {
                    LOG.error(TITLE, e);
                }
            }
            // 删除临时xml文件
            workbook.dispose();
        }
        return file;
    }
    /**
     * 上传文件
     * 
     * @param file
     * @param contentType
     * @return
     */
    private FileResponseBo uploadFile(File file, String contentType) {
        String uploadUrl = Config.get(UPLOAD_URL);
        LOG.info(TITLE, "uploadUrl:{}", uploadUrl);
        HttpPost httpPost = new HttpPost(uploadUrl);
        httpPost.setHeader(CONTENT_TYPE, contentType);
        FileEntity fileEntity = new FileEntity(file);
        httpPost.setEntity(fileEntity);
        String res = HttpClientHelper.getInstance().doPost(httpPost);
        LOG.info(TITLE, "res:{}", res);
        return JSONUtil.parse(res, FileResponseBo.class);
    }
}

        前端使用Window.open就可以打开下载了

三、前端

        前端可以参考前端（一）Vue+Java实现动态表格展示_java+vue显示数据库数据-CSDN博客

四、效果

        只要导入导出的数据变一下，表格就会自动展示不同的列和数据

五、总结

        很多东西做成通用的会比较方便，但是比较适合内部项目，减少人力