Easyexcel导出带下拉框选项excel模板（解决下拉框超50个的问题）

1、为了避免excel下拉框选项过多会导致内容不显示（或者生成的时候报错：String literals in formulas can't be bigger than 255 characters ASCII easyexcel），将下拉框的内容都存储在另一个新建的固定的sheet页，再通过引用公式关联单元格的下拉框内容，从而形成能够存储多数值的下拉框。

2、导出代码（这里演示的是一次性导出多个模板，采用压缩包的形式下载，并且表头是动态的）：

/**
     * 导出模板
     * @param response
     * @param businessViewId
     */
    @Override
    public void exportTemplate(HttpServletResponse response, String businessViewId) throws IOException {
        String[] split = businessViewId.split(",");

        String zipName = "模板.zip";
        response.setCharacterEncoding("utf-8");
        response.setContentType(MediaType.APPLICATION_OCTET_STREAM_VALUE);
        response.setHeader("Content-Disposition", "attachment;filename*=UTF-8''" + URLEncoder.encode(zipName, "UTF-8"));
        ServletOutputStream out = response.getOutputStream();
        ZipOutputStream zipOutputStream = new ZipOutputStream(out);

        for (String viewid : split) {

            List field = baseMapper.findBusinessFieldByViewId(viewid);
            //根据表id查询父表id
            String parentId = this.findParentIdByViewId(viewid);
            List parentFieldList = baseMapper.findBusinessFieldByViewId(parentId);
            //定义表头
            List> headList = new ArrayList<>();
            //定义数据体
            List> dataList = new ArrayList<>();
            // 指定标红色的列
            List columns = Arrays.asList();
            // 指定批注
            HashMap annotationsMap = new HashMap<>();
            HashMap> dropDownMap = new HashMap<>();
            //主表字段
            for (int i = 0;i tDataDictionaries = tDataDictionaryTempMapper.getNameByPid(businessField.getDictionary());
//                        存储需要下拉框的值，这里的key是需要设置为下拉框的列数，value是下拉框的值，是list
                        if (tDataDictionaries != null && tDataDictionaries.size()>0) {
                            dropDownMap.put(i,tDataDictionaries);
                        }
                    }
                }
            }
            //子表字段
            for (int i = 0;i tDataDictionaries = tDataDictionaryTempMapper.getNameByPid(businessField.getDictionary());
//                         存储需要下拉框的值，这里的key是需要设置为下拉框的列数，value是下拉框的值，是list
                        if (tDataDictionaries != null && tDataDictionaries.size()>0){
                            dropDownMap.put(i+parentFieldList.size(),tDataDictionaries);
                        }
                    }
                }
            }
            ExcelWriter excelWriter = EasyExcel.write().excelType(ExcelTypeEnum.XLS).build();
            //构建一个sheet页
            WriteSheet writeSheet = EasyExcel.writerSheet("sheet1").build();
//            TltleHandler titleHandler = new TltleHandler(columns, IndexedColors.RED.index,annotationsMap,dropDownMap);
//            ExayExcelUtils.writeExcelWithModel(response.getOutputStream(), dataList, headList, "sheet1", (CellWriteHandler) titleHandler);
// 头的策略
            WriteCellStyle headWriteCellStyle = new WriteCellStyle();
            // 单元格策略
            WriteCellStyle contentWriteCellStyle = new WriteCellStyle();
            // 初始化表格样式
            HorizontalCellStyleStrategy horizontalCellStyleStrategy = new HorizontalCellStyleStrategy(headWriteCellStyle, contentWriteCellStyle);
// SelectSheetWriteHandler(dropDownMap)  是设置下拉框的类
            WriteTable writeTable = EasyExcel.writerTable(0).head(headList).registerWriteHandler(horizontalCellStyleStrategy).registerWriteHandler(new SelectSheetWriteHandler(dropDownMap)).needHead(Boolean.TRUE).build();
            excelWriter.write(dataList, writeSheet, writeTable);
            // 开始导出
//            excelWriterSheetBuilder.doWrite(dataList);
            Workbook workbook = excelWriter.writeContext().writeWorkbookHolder().getWorkbook();
            //创建压缩文件
            String nameByid = baseMapper.getNameByid(viewid);
            ZipEntry zipEntry = new ZipEntry(nameByid+".xls");
            zipOutputStream.putNextEntry(zipEntry);

            //将excel对象以流的形式写入压缩流
            workbook.write(zipOutputStream);

        }

        zipOutputStream.flush();
        zipOutputStream.close();

    }

3、设置下拉框的类：

package com.customization.BusinessFilIdExcel.utils;

import com.alibaba.excel.write.handler.SheetWriteHandler;
import com.alibaba.excel.write.metadata.holder.WriteSheetHolder;
import com.alibaba.excel.write.metadata.holder.WriteWorkbookHolder;
import org.apache.poi.hssf.usermodel.HSSFDataValidation;
import org.apache.poi.ss.usermodel.*;
import org.apache.poi.ss.util.CellRangeAddressList;

import java.util.List;
import java.util.Map;

public class SelectSheetWriteHandler implements SheetWriteHandler {

    private Map> selectMap;

    private int index;

    private char[] alphabet = new char[]{'A', 'B', 'C', 'D', 'E', 'F', 'G', 'H', 'I', 'J', 'K', 'L',
            'M', 'N', 'O', 'P', 'Q', 'R', 'S', 'T', 'U', 'V', 'W', 'X', 'Y', 'Z'};

    public SelectSheetWriteHandler(Map> selectMap) {
        this.selectMap = selectMap;
        this.index = 0;
    }

    @Override
    public void beforeSheetCreate(WriteWorkbookHolder writeWorkbookHolder, WriteSheetHolder writeSheetHolder) {

    }

    @Override
    public void afterSheetCreate(WriteWorkbookHolder writeWorkbookHolder, WriteSheetHolder writeSheetHolder) {
        if (selectMap == null || selectMap.size() == 0) {
            return;
        }
        // 需要设置下拉框的sheet页
        Sheet curSheet = writeSheetHolder.getSheet();
        DataValidationHelper helper = curSheet.getDataValidationHelper();
        String dictSheetName = "字典sheet";

        Workbook workbook = writeWorkbookHolder.getWorkbook();

        // 数据字典的sheet页
        Sheet dictSheet = workbook.createSheet(dictSheetName);
        // 从第二个工作簿开始隐藏，为了用户的友好性，将字典sheet隐藏掉
        this.index++;
        // 设置隐藏
        workbook.setSheetHidden(this.index, true);
        for (Map.Entry> entry : selectMap.entrySet()) {
            // 设置下拉单元格的首行、末行、首列、末列
            CellRangeAddressList rangeAddressList = new CellRangeAddressList(1, 65533, entry.getKey(), entry.getKey());
            int rowLen = entry.getValue().size();
            // 设置字典sheet页的值 每一列一个字典项
            for (int i = 0; i < rowLen; i++) {
                Row row = dictSheet.getRow(i);
                if (row == null) {
                    row = dictSheet.createRow(i);
                }
                row.createCell(entry.getKey()).setCellValue(entry.getValue().get(i));
            }
            String excelColumn = getExcelColumn(entry.getKey());
            // 下拉框数据来源 eg:字典sheet!$B1:$B2
            String refers = dictSheetName + "!$" + excelColumn + "$1:$" + excelColumn + "$" + rowLen;
            // 创建可被其他单元格引用的名称
            Name name = workbook.createName();
            // 设置名称的名字
            name.setNameName("dict" + entry.getKey());
            // 设置公式
            name.setRefersToFormula(refers);
            // 设置引用约束
            DataValidationConstraint constraint = helper.createFormulaListConstraint("dict" + entry.getKey());
            // 设置约束
            DataValidation validation = helper.createValidation(constraint, rangeAddressList);
            if (validation instanceof HSSFDataValidation) {
                validation.setSuppressDropDownArrow(false);
            } else {
                validation.setSuppressDropDownArrow(true);
                validation.setShowErrorBox(true);
            }
            // 阻止输入非下拉框的值
            validation.setErrorStyle(DataValidation.ErrorStyle.STOP);
            validation.createErrorBox("提示", "此值与单元格定义格式不一致！");
            // 添加下拉框约束
            writeSheetHolder.getSheet().addValidationData(validation);
        }

    }

    /**
     * 将数字列转化成为字母列
     *
     * @param num
     * @return
     */
    private String getExcelColumn(int num) {
        String column = "";
        int len = alphabet.length - 1;
        int first = num / len;
        int second = num % len;
        if (num <= len) {
            column = alphabet[num] + "";
        } else {
            column = alphabet[first - 1] + "";
            if (second == 0) {
                column = column + alphabet[len] + "";
            } else {
                column = column + alphabet[second - 1] + "";
            }
        }
        return column;

    }

}

4、效果如下：