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当数据量比较大时，例如数据量达到百万级，传统的一次读取到内存中在写入excel文件的方法便不再适用了，可能会导致内存溢出；而且一次性将数据写入一张sheet工作表也不太好。
但我们可以选择数据分片的方式批量写入多个工作表。
测试数据100w条，写入到Excel表中，分成5个sheet表，每个sheet表20w条。

1.引入依赖

pom.xml

    <dependencies><!-- web --><dependency><groupId>org.springframework.boot</groupId><artifactId>spring-boot-starter-web</artifactId></dependency><!-- mybatis --><dependency><groupId>org.mybatis.spring.boot</groupId><artifactId>mybatis-spring-boot-starter</artifactId><version>2.2.2</version></dependency><dependency><groupId>org.springframework.boot</groupId><artifactId>spring-boot-starter-test</artifactId><scope>test</scope></dependency><!-- alibaba easyexcel --><dependency><groupId>com.alibaba</groupId><artifactId>easyexcel</artifactId><version>3.0.5</version><exclusions><exclusion><groupId>org.apache.poi</groupId><artifactId>poi</artifactId></exclusion><exclusion><groupId>org.apache.poi</groupId><artifactId>poi-ooxml</artifactId></exclusion><exclusion><groupId>org.apache.poi</groupId><artifactId>poi-ooxml-schemas</artifactId></exclusion></exclusions></dependency><!-- lombok --><dependency><groupId>org.projectlombok</groupId><artifactId>lombok</artifactId><version>1.18.24</version></dependency><!-- mybatis-plus --><dependency><groupId>com.baomidou</groupId><artifactId>mybatis-plus-boot-starter</artifactId><version>3.5.3</version></dependency><!-- jdbc --><dependency><groupId>org.springframework.boot</groupId><artifactId>spring-boot-starter-jdbc</artifactId></dependency><!--Mysql依赖包--><dependency><groupId>mysql</groupId><artifactId>mysql-connector-java</artifactId></dependency><!-- hutool --><dependency><groupId>cn.hutool</groupId><artifactId>hutool-all</artifactId><version>5.7.16</version></dependency></dependencies>

2. Controller/Service/Mapper

实体类User

import com.alibaba.excel.annotation.ExcelProperty;
import com.baomidou.mybatisplus.annotation.TableId;
import com.baomidou.mybatisplus.annotation.TableName;
import lombok.AllArgsConstructor;
import lombok.Builder;
import lombok.Data;
import lombok.NoArgsConstructor;import java.io.Serializable;
import java.time.LocalDateTime;@NoArgsConstructor
@AllArgsConstructor
@Data
@TableName("user")
public class User implements Serializable {@TableId("id")@ExcelProperty("id")private Long id;@ExcelProperty("username")private String username;@ExcelProperty("password")private String password;@ExcelProperty("email")private String email;@ExcelProperty("phoneNumber")private String phoneNumber;@ExcelProperty("createdAt")private LocalDateTime createdAt;@ExcelProperty(value = "updatedAt")private LocalDateTime updatedAt;}

UserCtrl

import cn.hutool.core.collection.CollUtil;
import cn.hutool.core.lang.UUID;
import com.alibaba.excel.EasyExcel;
import com.alibaba.excel.ExcelWriter;
import com.alibaba.excel.write.metadata.WriteSheet;
import com.alibaba.excel.write.style.column.LongestMatchColumnWidthStyleStrategy;
import com.example.excel.config.LocalDateTimeConverter;
import com.example.excel.domain.User;
import com.example.excel.mapper.UserMapper;
import com.example.excel.util.ExcelConstants;
import lombok.RequiredArgsConstructor;
import lombok.extern.slf4j.Slf4j;
import org.springframework.web.bind.annotation.RequestMapping;
import org.springframework.web.bind.annotation.RestController;import javax.servlet.http.HttpServletResponse;
import java.io.IOException;
import java.io.OutputStream;
import java.util.List;
import java.util.concurrent.CompletableFuture;
import java.util.concurrent.CountDownLatch;
import java.util.concurrent.Executor;/*** @author: hong.jian* 09-28 11:37*/
@RestController
@RequiredArgsConstructor
@Slf4j
@RequestMapping("/export")
public class UserCtrl {private final UserMapper userMapper;private final Executor exportThreadPoolExecutor;
}

UserService 和 UserServiceImpl

public interface UserService extends IService<User> {}@Service
@RequiredArgsConstructor
public class UserServiceImpl extends ServiceImpl<UserMapper, User> implements UserService {private final UserMapper userMapper;}

UserMapper

@Mapper
public interface UserMapper extends BaseMapper<User> {List<User> selfSelectList(@Param("currentPage") int currentPage, @Param("pageSize") int pageSize);}

UserMapper.xml

<?xml version="1.0" encoding="UTF-8"?>
<!DOCTYPE mapper PUBLIC "-//mybatis.org//DTD Mapper 3.0//EN""http://mybatis.org/dtd/mybatis-3-mapper.dtd">
<mapper namespace="com.example.excel.mapper.UserMapper"><!-- 使用覆盖索引处理深度分页 --><select id="seleSelectList"  resultType="com.example.excel.domain.User">SELECTu.id,u.username,u.PASSWORD,u.email,u.phone_number,u.created_at,u.updated_atFROMUSER u,( SELECT t.id FROM USER t ORDER BY t.id LIMIT #{currentPage}, #{pageSize} ) AS dWHEREu.id = d.id;</select></mapper>

LocalDateTime时间字段转换器

import com.alibaba.excel.converters.Converter;
import com.alibaba.excel.metadata.GlobalConfiguration;
import com.alibaba.excel.metadata.data.WriteCellData;
import com.alibaba.excel.metadata.data.ReadCellData;
import com.alibaba.excel.metadata.property.ExcelContentProperty;import java.time.LocalDateTime;
import java.time.format.DateTimeFormatter;/*** 自定义LocalDateTime时间字段类型转换器*/
public class LocalDateTimeConverter implements Converter<LocalDateTime> {private static final DateTimeFormatter FORMATTER = DateTimeFormatter.ofPattern("yyyy-MM-dd HH:mm:ss");@Overridepublic Class<LocalDateTime> supportJavaTypeKey() {return LocalDateTime.class;}@Overridepublic WriteCellData<?> convertToExcelData(LocalDateTime value, ExcelContentProperty contentProperty, GlobalConfiguration globalConfiguration) {if (value != null) {return new WriteCellData<>(value.format(FORMATTER));}return new WriteCellData<>("");}@Overridepublic LocalDateTime convertToJavaData(ReadCellData<?> cellData, ExcelContentProperty contentProperty, GlobalConfiguration globalConfiguration) {if (cellData.getStringValue() != null) {return LocalDateTime.parse(cellData.getStringValue(), FORMATTER);}return null;}
}

3. 编写Controller方法

    @RequestMapping("/test")public void export(HttpServletResponse response) throws IOException {log.info("*********统计查询列表导出开始！**************");long start = System.currentTimeMillis();// 文件名String fileName = String.valueOf(UUID.randomUUID());OutputStream outputStream = null;try {// 总记录数:实际中需要根据查询条件进行统计即可:一共多少条long totalCount = userMapper.selectCount(null);// 每一个Sheet存放20w条数据Integer sheetDataRows = ExcelConstants.PER_SHEET_ROW_COUNT;// 每次写入的数据量10w,每页查询10WInteger writeDataRows = ExcelConstants.PER_WRITE_ROW_COUNT;// 计算需要的Sheet数量long 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long 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++) {log.info("*********统计查询列表第" + (i + 1) + "页导出开始！**************");// 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lastSheetWriteCountfor (int j = 0; j < (i != sheetNum - 1 ? oneSheetWriteCount : lastSheetWriteCount); j++) {// 分页查询一次10w// 设置偏移量int currentPage = (j + oneSheetWriteCount * i) * writeDataRows;// 设置每页大小int pageSize = writeDataRows;// 使用覆盖索引避免深度分页List<User> userList = userMapper.selfSelectList(currentPage, pageSize);if (CollUtil.isEmpty(userList)) {  // 记录集合判空continue;}// 写入到excel:// 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WriteSheet writeSheet = EasyExcel.writerSheet(i, "Sheet" + (i + 1)).head(User.class).registerWriteHandler(new LongestMatchColumnWidthStyleStrategy())   // 自动调整列宽.registerConverter(new LocalDateTimeConverter())    // 时间字段转换器// .includeColumnFiledNames()  // 只导出指定字段集合// .excludeColumnFiledNames()  // 排除指定字段集合.build();excelWriter.write(userList, writeSheet);}log.info("*********统计查询列表第" + (i + 1) + "页导出结束！**************");}// 下载EXCEL，返回给前端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();log.info("*********统计查询列表导出结束！**************");log.info("耗时：" + (System.currentTimeMillis() - start));} catch (Exception e) {e.printStackTrace();} finally {if (outputStream != null) {outputStream.close();}}}

4. 测试

100w条数据导出约27s，还是有点慢。

9-28 17:49:27.847  INFO 120052 --- [nio-8080-exec-1] com.example.excel.controller.UserCtrl    : *********统计查询列表导出开始！**************
2024-09-28 17:49:28.744  INFO 120052 --- [nio-8080-exec-1] com.example.excel.controller.UserCtrl    : *********统计查询列表第1页导出开始！**************
2024-09-28 17:49:32.857  INFO 120052 --- [nio-8080-exec-1] com.example.excel.controller.UserCtrl    : *********统计查询列表第1页导出结束！**************
2024-09-28 17:49:32.857  INFO 120052 --- [nio-8080-exec-1] com.example.excel.controller.UserCtrl    : *********统计查询列表第2页导出开始！**************
2024-09-28 17:49:36.955  INFO 120052 --- [nio-8080-exec-1] com.example.excel.controller.UserCtrl    : *********统计查询列表第2页导出结束！**************
2024-09-28 17:49:36.955  INFO 120052 --- [nio-8080-exec-1] com.example.excel.controller.UserCtrl    : *********统计查询列表第3页导出开始！**************
2024-09-28 17:49:41.007  INFO 120052 --- [nio-8080-exec-1] com.example.excel.controller.UserCtrl    : *********统计查询列表第3页导出结束！**************
2024-09-28 17:49:41.007  INFO 120052 --- [nio-8080-exec-1] com.example.excel.controller.UserCtrl    : *********统计查询列表第4页导出开始！**************
2024-09-28 17:49:45.109  INFO 120052 --- [nio-8080-exec-1] com.example.excel.controller.UserCtrl    : *********统计查询列表第4页导出结束！**************
2024-09-28 17:49:45.109  INFO 120052 --- [nio-8080-exec-1] com.example.excel.controller.UserCtrl    : *********统计查询列表第5页导出开始！**************
2024-09-28 17:49:49.272  INFO 120052 --- [nio-8080-exec-1] com.example.excel.controller.UserCtrl    : *********统计查询列表第5页导出结束！**************
2024-09-28 17:49:55.630  INFO 120052 --- [nio-8080-exec-1] com.example.excel.controller.UserCtrl    : *********统计查询列表导出结束！**************
2024-09-28 17:49:55.631  INFO 120052 --- [nio-8080-exec-1] com.example.excel.controller.UserCtrl    : 耗时：27784

5. 思考

引入线程池

    @Beanpublic Executor exportThreadPoolExecutor(){return  new ThreadPoolExecutor(5,10,10,TimeUnit.SECONDS,new ArrayBlockingQueue<>(100),new ThreadPoolExecutor.CallerRunsPolicy());}

并在UserController中注入

使用线程池优化代码

    @RequestMapping("/test2")public void export2(HttpServletResponse response) throws IOException {log.info("*********统计查询列表导出开始！**************");long start = System.currentTimeMillis();String fileName = String.valueOf(UUID.randomUUID());OutputStream outputStream = null;try {long totalCount = userMapper.selectCount(null);Integer sheetDataRows = ExcelConstants.PER_SHEET_ROW_COUNT;Integer writeDataRows = ExcelConstants.PER_WRITE_ROW_COUNT;long sheetNum = (totalCount + sheetDataRows - 1) / sheetDataRows;Integer oneSheetWriteCount = sheetDataRows / writeDataRows;long lastSheetWriteCount = totalCount % sheetDataRows == 0 ? oneSheetWriteCount :(totalCount % sheetDataRows + writeDataRows - 1) / writeDataRows;outputStream = response.getOutputStream();ExcelWriter excelWriter = EasyExcel.write(outputStream).build();// 信号枪，配合多线程实现并发编程CountDownLatch latch = new CountDownLatch((int) sheetNum);for (int i = 0; i < sheetNum; i++) {int finalI = i;CompletableFuture.runAsync(() -> {log.info("*********统计查询列表第" + (finalI + 1) + "页导出开始！**************");WriteSheet writeSheet = EasyExcel.writerSheet(finalI, "Sheet" + (finalI + 1)).head(User.class).registerWriteHandler(new LongestMatchColumnWidthStyleStrategy()).registerConverter(new LocalDateTimeConverter()).build();try {for (int j = 0; j < (finalI != sheetNum - 1 ? oneSheetWriteCount : lastSheetWriteCount); j++) {int currentPage = (j + oneSheetWriteCount * finalI) * writeDataRows;List<User> userList = userMapper.selfSelectList(currentPage, writeDataRows);if (CollUtil.isEmpty(userList)) {continue;}// 加锁实现互斥写入，确保线程安全synchronized (excelWriter) {excelWriter.write(userList, writeSheet);}}} finally {latch.countDown();log.info("*********统计查询列表第" + (finalI + 1) + "页导出结束！**************");}}, exportThreadPoolExecutor);   // 尝试引入多线程}latch.await();response.setContentType("application/octet-stream");response.setCharacterEncoding("utf-8");response.setHeader("Content-disposition", "attachment;filename*=utf-8''" + fileName + ".xlsx");excelWriter.finish();outputStream.flush();} catch (Exception e) {e.printStackTrace();} finally {if (outputStream != null) {outputStream.close();}}log.info("*********统计查询列表导出结束！**************");log.info("耗时：" + (System.currentTimeMillis() - start));}

再次测试，耗时约20s

2024-09-28 18:05:54.239  INFO 53952 --- [nio-8080-exec-1] com.example.excel.controller.UserCtrl    : *********统计查询列表导出开始！**************
2024-09-28 18:05:55.132  INFO 53952 --- [pool-1-thread-2] com.example.excel.controller.UserCtrl    : *********统计查询列表第2页导出开始！**************
2024-09-28 18:05:55.132  INFO 53952 --- [pool-1-thread-3] com.example.excel.controller.UserCtrl    : *********统计查询列表第3页导出开始！**************
2024-09-28 18:05:55.132  INFO 53952 --- [pool-1-thread-4] com.example.excel.controller.UserCtrl    : *********统计查询列表第4页导出开始！**************
2024-09-28 18:05:55.132  INFO 53952 --- [pool-1-thread-5] com.example.excel.controller.UserCtrl    : *********统计查询列表第5页导出开始！**************
2024-09-28 18:05:55.132  INFO 53952 --- [pool-1-thread-1] com.example.excel.controller.UserCtrl    : *********统计查询列表第1页导出开始！**************
2024-09-28 18:06:04.341  INFO 53952 --- [pool-1-thread-3] com.example.excel.controller.UserCtrl    : *********统计查询列表第3页导出结束！**************
2024-09-28 18:06:05.483  INFO 53952 --- [pool-1-thread-4] com.example.excel.controller.UserCtrl    : *********统计查询列表第4页导出结束！**************
2024-09-28 18:06:06.591  INFO 53952 --- [pool-1-thread-5] com.example.excel.controller.UserCtrl    : *********统计查询列表第5页导出结束！**************
2024-09-28 18:06:07.795  INFO 53952 --- [pool-1-thread-1] com.example.excel.controller.UserCtrl    : *********统计查询列表第1页导出结束！**************
2024-09-28 18:06:08.871  INFO 53952 --- [pool-1-thread-2] com.example.excel.controller.UserCtrl    : *********统计查询列表第2页导出结束！**************
2024-09-28 18:06:14.907  INFO 53952 --- [nio-8080-exec-1] com.example.excel.controller.UserCtrl    : *********统计查询列表导出结束！**************
2024-09-28 18:06:14.907  INFO 53952 --- [nio-8080-exec-1] com.example.excel.controller.UserCtrl    : 耗时：20667

可以发现，性能有提升，但提升不是很明显。我个人理解是为了避免多个线程同时写入excel产生的线程安全问题，采用了加锁的方式，确保线程间使用excelwriter写入excel文件的操作是互斥的，这导致性能收到了影响。

参考链接：使用EasyExcel实现excel导出，支持百万大数据量导出