easyexcel将对象处理为多列，自增序列

概述

主要记录在开发中遇到的问题：使用easyexcel导出excel，一般数据都是保存在数据库中，如果查询返回的是一个实体类，且里面有嵌套的实体类对象，这时导出的时候要先对查询出的数据进行业务逻辑处理，让它符合导出规范，但是当数据量很大时，容易jvm内存，easyexcel(CellDataTypeEnum)只支持基本数据类型的导入，如图1-1所示，可以通过自定义数据类型(Converter)进行转换，但是这样只能返回一种基本的数据类型，像这种实体类里面通常会有很多信息，如果都要导出，这种方式也不合适。目前我能想到的方式是通过它提供的各种拦截器处理，大概流程如下：

通过自定义数据类型将实体类转换为String类型，然后通过拦截器将字符串拆分，添加对应列的数据。

图1-1 excel内部支持的数据类型

代码展示

• excel日期转换类

import com.alibaba.excel.converters.Converter;
import com.alibaba.excel.converters.WriteConverterContext;
import com.alibaba.excel.enums.CellDataTypeEnum;
import com.alibaba.excel.metadata.data.WriteCellData;

import java.text.SimpleDateFormat;
import java.util.Date;

/**
 * @Description excel日期转换类 即将Mongo中类型为long的时间戳转化为yyyy-MM-dd HH:mm:ss时间
 * @author HuangAnting
 * @date 2022/4/8 10:16
*/
public class DateConverter implements Converter {
    @Override
    public Class supportJavaTypeKey() {
        //对象属性类型
        return Long.class;
    }

    @Override
    public CellDataTypeEnum supportExcelTypeKey() {
        //CellData属性类型
        return CellDataTypeEnum.STRING;
    }
    @Override
    public WriteCellData convertToExcelData(WriteConverterContext context) throws Exception {
        //对象属性转CellData
        Long cellValue = context.getValue();
        new SimpleDateFormat("yyyy-MM-dd HH:mm:ss").format(new Date(cellValue));
        if (cellValue == null) {
            return new WriteCellData<>("");
        } else {
            return new WriteCellData<>( new SimpleDateFormat("yyyy-MM-dd HH:mm:ss").format(new Date(cellValue)));
        }
    }
}

• 自增序号拦截器

import com.alibaba.excel.write.handler.RowWriteHandler;
import com.alibaba.excel.write.metadata.holder.WriteSheetHolder;
import com.alibaba.excel.write.metadata.holder.WriteTableHolder;
import org.apache.poi.ss.usermodel.*;

/**
 * @Description 自增序号拦截器
 * @author HuangAnting
 * @date 2022/4/12 17:27
*/
public class IndexRowWriteHandler implements RowWriteHandler {
    private static final String FIRST_CELL_NAME = "序号";
    /**
     * 序号的样式，与其他列保持一样的样式
     */
    private CellStyle firstCellStyle;
    private String description;
    /**
     * 列号
     */
    private int count = 0;
    public IndexRowWriteHandler(String description){
        this.description = description;
    }

    @Override
    public void afterRowDispose(WriteSheetHolder writeSheetHolder, WriteTableHolder writeTableHolder, Row row, Integer relativeRowIndex, Boolean isHead) {
        // 每一行首列单元格
        Cell indexCell = row.createCell(0);
        if(!isHead){
            indexCell.setCellValue(++count);
           try {
               row.getCell(3).setCellValue(description);
           }
           catch (Exception e){
           }
        }
        else {
            Workbook workbook = writeSheetHolder.getSheet().getWorkbook();
            firstCellStyle = firstCellStyle(workbook);
            indexCell.setCellValue(FIRST_CELL_NAME);
            indexCell.setCellStyle(firstCellStyle);
            writeSheetHolder.getSheet().setColumnWidth(0, 6 * 256);
        }
    }

    /**
     * excel首列序号列样式
     * @param workbook
     * @return
     */
    public  CellStyle firstCellStyle(Workbook workbook) {
        CellStyle cellStyle = workbook.createCellStyle();
        //居中
        cellStyle.setAlignment(HorizontalAlignment.CENTER);
        cellStyle.setVerticalAlignment(VerticalAlignment.CENTER);
        cellStyle.setFillPattern(FillPatternType.SOLID_FOREGROUND);
        // 灰色
        cellStyle.setFillForegroundColor(IndexedColors.GREY_25_PERCENT.getIndex());
        //设置边框
        cellStyle.setBorderBottom(BorderStyle.THIN);
        cellStyle.setBorderLeft(BorderStyle.THIN);
        cellStyle.setBorderRight(BorderStyle.THIN);
        cellStyle.setBorderTop(BorderStyle.THIN);
        //文字
        Font font = workbook.createFont();
        font.setBold(Boolean.TRUE);
        cellStyle.setFont(font);
        return cellStyle;
    }
}

• 实体类

import com.alibaba.excel.annotation.ExcelProperty;
import com.alibaba.excel.annotation.write.style.ColumnWidth;
import com.hat.easyexcel_export.excel.DateConverter;
import com.hat.easyexcel_export.excel.MonPointConverter;
import lombok.Data;

/**
 * @Description 导出实体类
 * @author HuangAnting
 * @date 2022/4/12 17:26
*/
@Data
public class Car {
    /** 名称*/
    @ExcelProperty(value = "名称",index = 1)
    private String name;
    /** 价格*/
    @ExcelProperty(value = "价格",index = 2)
    private Double price;
    /** 描述*/
    @ColumnWidth(15)
    @ExcelProperty(value = "描述",index = 3)
    private String description;
    /** 坐标*/
    @ExcelProperty(value = "坐标",converter = MonPointConverter.class,index = 4)
    private MonPoint monPoint;
    /** 日期*/
    @ExcelProperty(value = "日期",converter = DateConverter.class)
    private Long createDate;
}

• 自定义对象拦截器

import com.alibaba.excel.write.handler.RowWriteHandler;
import com.alibaba.excel.write.metadata.holder.WriteSheetHolder;
import com.alibaba.excel.write.metadata.holder.WriteTableHolder;
import com.alibaba.fastjson.JSONObject;
import com.hat.easyexcel_export.entity.MonPoint;
import org.apache.poi.ss.usermodel.*;


/**
 * @Description 行拦截器 将字符串的经纬度转换成两列数据
 * @author HuangAnting
 * @date 2022/4/12 17:26
*/
public class CustomRowWriteHandler implements RowWriteHandler {

    /**
     * 序号的样式，与其他列保持一样的样式
     */
    private CellStyle firstCellStyle;
    private static final String LON_CELL_NAME = "经度";
    private static final String LAT_CELL_NAME = "纬度";

    /**
     * 列号
     */
    @Override
    public void afterRowDispose(WriteSheetHolder writeSheetHolder, WriteTableHolder writeTableHolder, Row row, Integer integer, Boolean isHead) {
        Cell cell = row.getCell(4);
        row.removeCell(cell);
        Cell lon = row.createCell(4);
        Cell lat = row.createCell(5);
        if (!isHead) {
            String stringCellValue = cell.getStringCellValue();
            try {
                MonPoint monPoint = JSONObject.parseObject(stringCellValue, MonPoint.class);
                lon.setCellValue(monPoint.getLon());
                lat.setCellValue(monPoint.getLat());
            }
            catch (Exception e){
            }
        }else {
            Workbook workbook = writeSheetHolder.getSheet().getWorkbook();
            firstCellStyle = firstCellStyle(workbook);
            lon.setCellStyle(firstCellStyle);
            lat.setCellStyle(firstCellStyle);
            lon.setCellValue(LON_CELL_NAME);
            lat.setCellValue(LAT_CELL_NAME);
        }
    }

    /**
     * excel首列序号列样式
     *
     * @param workbook
     * @return
     */
    public CellStyle firstCellStyle(Workbook workbook) {
        CellStyle cellStyle = workbook.createCellStyle();
        //居中
        cellStyle.setAlignment(HorizontalAlignment.CENTER);
        cellStyle.setVerticalAlignment(VerticalAlignment.CENTER);
        cellStyle.setFillPattern(FillPatternType.SOLID_FOREGROUND);
        // 灰色
        cellStyle.setFillForegroundColor(IndexedColors.GREY_25_PERCENT.getIndex());
        //设置边框
        cellStyle.setBorderBottom(BorderStyle.THIN);
        cellStyle.setBorderLeft(BorderStyle.THIN);
        cellStyle.setBorderRight(BorderStyle.THIN);
        cellStyle.setBorderTop(BorderStyle.THIN);
        //文字
        Font font = workbook.createFont();
        font.setBold(Boolean.TRUE);
        cellStyle.setFont(font);
        return cellStyle;
    }
}

gitee地址：easyexcel_export

以上仅代表本人对easyexcel的认识和了解，欢迎大家批评指正。