笔者最近需要导出一百多万条数据到Excel，已经超出单张工作表的最大容量（2^20=1048576），需要导出到多个工作表或多个Excel文件。

海量数据导出面临的问题有以下几个：

1. 如果一次性查出所有数据，很可能内存溢出，所以需要分页导出，分页导出就必须解决大分页查询的性能问题。
   该问题网上有很多解决办法，本文不涉及。

2. 如果使用POI进行数据导出，内存、CPU占用都很高，而且速度很慢，所以采用EasyExcel进行数据导出。在上一篇使用EasyExcel读写Excel文件中，数据是一次性写入的，本文介绍EasyExcel多次写入数据的方法。

3. 将多个EasyExcel的数据写入到zip文件中。通过将EasyExcel写入到ByteArrayOutputStream，再将ByteArrayOutputStream转成byte数组，写入到zip中。

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1.在pom.xml中添加POI相关依赖

        <!-- easyexcel --><dependency><groupId>com.alibaba</groupId><artifactId>easyexcel-core</artifactId><version>3.3.2</version></dependency>

2.实体类

package com.example.study.entity;import com.alibaba.excel.annotation.ExcelProperty;
import com.fasterxml.jackson.annotation.JsonFormat;
import lombok.Getter;
import lombok.Setter;import java.util.Date;@Getter
@Setter
public class StudentEntity {@ExcelProperty(value = "id", order = 1)private Integer id;@ExcelProperty(value = "生日", order = 4)@JsonFormat(pattern = "yyyy-MM-dd HH:mm:ss", timezone = "GMT+8")private Date birthday;@ExcelProperty(value = "名字", order = 2)private String name;@ExcelProperty(value = "性别", order = 3)private String sex;private String desc;private String extra;
}

3.写入数据

package com.example.study.common;import com.alibaba.excel.EasyExcel;
import com.alibaba.excel.ExcelWriter;
import com.alibaba.excel.write.metadata.WriteSheet;
import com.example.study.entity.StudentEntity;import java.io.ByteArrayOutputStream;
import java.io.FileOutputStream;
import java.io.IOException;
import java.util.ArrayList;
import java.util.Date;
import java.util.HashSet;
import java.util.List;
import java.util.Set;
import java.util.zip.ZipEntry;
import java.util.zip.ZipOutputStream;public class EasyExcelWriteToZipDemo {public static void main(String[] args) {String writeExcel = "F:\\tmp\\batch_export.zip";write(writeExcel);}private static void write(String writeExcel) {// 设置不需要导出的字段Set<String> excludeColumnFieldNames = new HashSet<>();excludeColumnFieldNames.add("desc");excludeColumnFieldNames.add("extra");WriteSheet sheet = EasyExcel.writerSheet("花名册").excludeColumnFieldNames(excludeColumnFieldNames).needHead(Boolean.TRUE).build();ByteArrayOutputStream baos = new ByteArrayOutputStream();ExcelWriter workbook = EasyExcel.write(baos, StudentEntity.class).build();int sheetMaxSize = 1001;int currentExcelSize = 0;int count = 0;int total = 3111;int fileIndex = 1;try (FileOutputStream fos = new FileOutputStream(writeExcel);ZipOutputStream zos = new ZipOutputStream(fos)) {while (count < total) {List<StudentEntity> page = getPage(count + 1, total);if (currentExcelSize + page.size() > sheetMaxSize) {// 超过单个文件最大数据条数后，写入到zip文件，并将当前页面数据写入新的excel文件workbook.close();zos.putNextEntry(new ZipEntry(String.format("数据导出文件_%s.xlsx", fileIndex++)));zos.write(baos.toByteArray());baos = new ByteArrayOutputStream();workbook = EasyExcel.write(baos, StudentEntity.class).build();currentExcelSize = page.size();} else {currentExcelSize += page.size();}workbook.write(page, sheet);count += page.size();}if (currentExcelSize > 0) {workbook.close();zos.putNextEntry(new ZipEntry(String.format("数据导出文件_%s.xlsx", fileIndex++)));zos.write(baos.toByteArray());}zos.flush();fos.flush();} catch (IOException exception) {exception.printStackTrace();}}private static List<StudentEntity> getPage(int lastMaxId, int total) {List<StudentEntity> page = new ArrayList<>();for (int index = lastMaxId; index < Math.min(lastMaxId + 100, total + 1); index++) {StudentEntity student = new StudentEntity();student.setId(index);student.setName("名字_" + index);student.setSex(index % 2 == 0 ? "女" : "男");student.setBirthday(new Date());student.setDesc("test desc");student.setExtra("test extra");page.add(student);}return page;}
}