使用EasyExcel实现excel导出，支持百万大数据量导出-----超简单

通过设置sheet数量，完成分批导出，每个sheet存100万数据，每次查询插入20万数据，避免超时，内存溢出等问题，可以根据服务器配置调整参数设置。
1.引入依赖

            <dependency>
                <groupId>com.alibaba</groupId>
                <artifactId>easyexcel</artifactId>
                <version>3.0.5</version>
            </dependency>

2.创建对应的实体类
@ExcelProperty设置的就是导出的列名，还可以设置排序等等

@Data
@NoArgsConstructor
@AllArgsConstructor
public class AltitudeMonExportExcelVO implements Serializable {

    @ExcelProperty(value = "站名")
    private String cname;

    @ExcelProperty(value = "站号")
    private String v01301;

    @ExcelProperty(value = "月平均气温(气温)")
    private String v12001_701="0";

    @ExcelProperty(value = "月平均气压")
    private String v10004_701="0";

    @ExcelProperty(value = "月平均相对湿度(相对湿度)")
    private String v13003_701="0";

    @ExcelProperty(value = "月平均温度露点差(露点温度)")
    private String v12301_701="0";
}

3.核心导出代码

public void exportSurfList2(StatisticsRequestVo requestVo,HttpServletResponse response) throws IOException {
        log.info("*********地面统计查询列表导出开始！**************");
        //文件名
        String fileName =String.valueOf(System.currentTimeMillis());

        OutputStream outputStream =null;
        try {
            //记录总数:实际中需要根据查询条件进行统计即可:一共多少条
            int totalCount=mapper.seleCount();
            //每一个Sheet存放100w条数据
            Integer sheetDataRows = ExcelConstants.PER_SHEET_ROW_COUNT;
            //每次写入的数据量20w,每页查询20W
            Integer writeDataRows = ExcelConstants.PER_WRITE_ROW_COUNT;
            //计算需要的Sheet数量
            Integer sheetNum = totalCount % sheetDataRows == 0 ? (totalCount / sheetDataRows) : (totalCount / sheetDataRows + 1);
            //计算一般情况下每一个Sheet需要写入的次数(一般情况不包含最后一个sheet,因为最后一个sheet不确定会写入多少条数据)
            Integer oneSheetWriteCount = sheetDataRows / writeDataRows;
            //计算最后一个sheet需要写入的次数
            Integer lastSheetWriteCount = totalCount % sheetDataRows == 0 ? oneSheetWriteCount : (totalCount % sheetDataRows % writeDataRows == 0 ? (totalCount / sheetDataRows / writeDataRows) : (totalCount / sheetDataRows / writeDataRows + 1));
            outputStream = response.getOutputStream();
            //必须放到循环外，否则会刷新流
            ExcelWriter excelWriter = EasyExcel.write(outputStream).build();
            //开始分批查询分次写入
            for (int i = 0; i < sheetNum; i++) {
                //创建Sheet
                WriteSheet sheet = new WriteSheet();
                sheet.setSheetName("Sheet"+i);
                sheet.setSheetNo(i);
                //循环写入次数: j的自增条件是当不是最后一个Sheet的时候写入次数为正常的每个Sheet写入的次数,如果是最后一个就需要使用计算的次数lastSheetWriteCount
                for (int j = 0; j < (i != sheetNum - 1 ? oneSheetWriteCount : lastSheetWriteCount); j++) {
                    //分页查询一次20w
                    Page page1 = new Page(j + 1 + oneSheetWriteCount * i, writeDataRows);
                    //查询分页列表---按照自己的业务查列表，分页这个一定要使用这个：page1.getPageNum(),page1.getPageSize()！！！
                    List<Map<String, Object>> list = mapper.selectList(page1.getPageNum(),page1.getPageSize());
                    List<AltitudeMonExportExcelVO > SurfDayList = new ArrayList<>();
                   //写入到excel:
                    /**************z只需要选择一种方式即可*****************/
                    //这里可以通过设置includeColumnFiledNames、excludeColumnFiledNames导出什么字段，可以动态配置，前端传过来那些列，就导出那些列
                    //方式1、只导出v01301这一列
                    Set<String> includeColumnFiledNames = new HashSet<String>();
                    includeColumnFiledNames.add("v01301");
                    WriteSheet writeSheet = EasyExcel.writerSheet(i, "Sheet" + (i + 1)).head(AltitudeMonExportExcelVO.class).includeColumnFiledNames(includeColumnFiledNames)
                            .registerWriteHandler(new LongestMatchColumnWidthStyleStrategy()).build();
                    //方式2、排除v01301这一列，其他的全部导出
                    Set<String> excludeColumnFiledNames = new HashSet<String>();
                    excludeColumnFiledNames.add("v01301");
                    WriteSheet writeSheet = EasyExcel.writerSheet(i, "Sheet" + (i + 1)).head(AltitudeMonExportExcelVO.class).excludeColumnFiledNames(includeColumnFiledNames)
                            .registerWriteHandler(new LongestMatchColumnWidthStyleStrategy()).build();
                    excelWriter.write(list, writeSheet);
                    //方式3、不做设置，全部导出
                    WriteSheet writeSheet = EasyExcel.writerSheet(i, "Sheet" + (i + 1)).head(AltitudeMonExportExcelVO.class)
                            .registerWriteHandler(new LongestMatchColumnWidthStyleStrategy()).build();
                    excelWriter.write(list, writeSheet);
                }
            }
            // 下载EXCEL，返回给前段stream流
            response.setContentType("application/octet-stream");
            response.setCharacterEncoding("utf-8");
            response.setHeader("Content-disposition", "attachment;filename*=utf-8''" + fileName + ".xlsx");
            excelWriter.finish();
            outputStream.flush();
            outputStream.close();
            log.info("*********地面统计查询列表导出结束！**************");
        } catch (Exception e) {
            e.printStackTrace();
        }finally {
            if (outputStream != null) {
                outputStream.close();
            }
        }

    }

4.配置类

public class ExcelConstants {
    //一个sheet装100w数据
    public static final Integer PER_SHEET_ROW_COUNT = 1000000;
    //每次查询20w数据，每次写入20w数据
    public static final Integer PER_WRITE_ROW_COUNT = 200000;
}

至此就完成导出。