前言

请等米下锅的同学直接阅读代码部分。

使用背景

最近项目组小伙伴们在开发使用Apache的Poi导出大批量数据时，总是出现内存溢出的情况。并且在生产环境，如果多个用户都导大批量数据报表时，服务器也很容易宕机。
虽然说Poi有SXSSFWorkbook这个类可以帮助我们导出较大批量的数据。其原理是用硬盘空间换内存这个样子。但是Excel2007最大一个sheet页也就支持1048576行。如果超出这个行数就需要去动态分多个sheet页去写入。由于我们是使用的模板去写入数据的，所以我们需要动态的克隆sheet页。之前只用过XSSFWorkbook类的cloneSheet方法。在阅读SXSSFWorkbook类的源码后，嗯！没实现，好的，算了算了。这也就是使用alibaba的开源项目EasyExcel的由来。EasyExcel重写了Poi对07版Excel的解析，能够原本一个3M的excel用POI sax依然需要100M左右内存降低到几M，并且再大的excel不会出现内存溢出。所以有摩托车不用，非要蹬自行车吗？那不是傻么。

这里也就不介绍EasyExcel了，没有什么比官网更详细了。请各位看官去官网详细阅读。

参考官方文档

• EasyExcel官方文档
• EasyExcel的github地址

代码部分

我们项目是使用Maven搭建的Springboot项目。

• Maven依赖：

<!-- https://mvnrepository.com/artifact/com.alibaba/easyexcel -->
 <dependency>
       <groupId>com.alibaba</groupId>
       <artifactId>easyexcel</artifactId>
       <version>2.2.6</version>
 </dependency>

• 工具类

1. EasyExcelUtil

java">package com.sinosoft.service.util;

import com.alibaba.excel.EasyExcel;
import com.alibaba.excel.ExcelWriter;
import com.alibaba.excel.support.ExcelTypeEnum;
import com.alibaba.excel.write.builder.ExcelWriterBuilder;
import com.alibaba.excel.write.builder.ExcelWriterSheetBuilder;
import com.alibaba.excel.write.metadata.WriteSheet;
import com.alibaba.excel.write.metadata.style.WriteCellStyle;
import com.alibaba.excel.write.metadata.style.WriteFont;
import com.alibaba.excel.write.style.HorizontalCellStyleStrategy;
import com.sinosoft.web.rest.util.SplitList;
import org.apache.poi.ss.usermodel.BorderStyle;
import org.apache.poi.ss.usermodel.HorizontalAlignment;
import org.apache.poi.ss.usermodel.IndexedColors;
import org.apache.poi.ss.usermodel.VerticalAlignment;
import org.slf4j.Logger;
import org.slf4j.LoggerFactory;

import javax.servlet.http.HttpServletResponse;
import java.io.*;
import java.net.URLEncoder;
import java.util.Date;
import java.util.List;

/**
 * @author QY
 * @since 2020-08-03
 * @description 使用easyExcel来导出xlsx的工具类
 */
public class EasyExcelUtil {

    private static final Logger log = LoggerFactory.getLogger(EasyExcelUtil.class);

    private static final int MAXROWS = 1000000;


    /**
     * 获取默认表头内容的样式
     * @return
     */
    private static HorizontalCellStyleStrategy getDefaultHorizontalCellStyleStrategy(){
        /** 表头样式 **/
        WriteCellStyle headWriteCellStyle = new WriteCellStyle();
        // 背景色（浅灰色）
        // 可以参考：https://www.cnblogs.com/vofill/p/11230387.html
        headWriteCellStyle.setFillForegroundColor(IndexedColors.GREY_25_PERCENT.getIndex());
        // 字体大小
        WriteFont headWriteFont = new WriteFont();
        headWriteFont.setFontHeightInPoints((short) 10);
        headWriteCellStyle.setWriteFont(headWriteFont);
        //设置表头居中对齐
        headWriteCellStyle.setHorizontalAlignment(HorizontalAlignment.CENTER);
        /** 内容样式 **/
        WriteCellStyle contentWriteCellStyle = new WriteCellStyle();
        // 内容字体样式（名称、大小）
        WriteFont contentWriteFont = new WriteFont();
        contentWriteFont.setFontName("宋体");
        contentWriteFont.setFontHeightInPoints((short) 10);
        contentWriteCellStyle.setWriteFont(contentWriteFont);
        //设置内容垂直居中对齐
        contentWriteCellStyle.setVerticalAlignment(VerticalAlignment.CENTER);
        //设置内容水平居中对齐
        contentWriteCellStyle.setHorizontalAlignment(HorizontalAlignment.CENTER);
        //设置边框样式
        contentWriteCellStyle.setBorderLeft(BorderStyle.THIN);
        contentWriteCellStyle.setBorderTop(BorderStyle.THIN);
        contentWriteCellStyle.setBorderRight(BorderStyle.THIN);
        contentWriteCellStyle.setBorderBottom(BorderStyle.THIN);
        // 头样式与内容样式合并
        return new HorizontalCellStyleStrategy(headWriteCellStyle, contentWriteCellStyle);
    }

    /**
     * 导出
     * @param response
     * @param data
     * @param fileName
     * @param sheetName
     * @param clazz
     * @throws Exception
     */
    public static void writeExcel(HttpServletResponse response, List<? extends Object> data, String fileName, String sheetName, Class clazz) throws Exception {
        long exportStartTime = System.currentTimeMillis();
        log.info("报表导出Size: "+data.size()+"条。");
        EasyExcel.write(getOutputStream(fileName, response), clazz).excelType(ExcelTypeEnum.XLSX).sheet(sheetName).registerWriteHandler(getDefaultHorizontalCellStyleStrategy()).doWrite(data);
        System.out.println("报表导出结束时间:"+ new Date()+";写入耗时: "+(System.currentTimeMillis()-exportStartTime)+"ms" );
    }

    /**
     * @author QiuYu
     * @createDate 2020-11-16
     * @param response
     * @param data  查询结果
     * @param fileName 导出文件名称
     * @param clazz 映射实体class类
     * @param <T>  查询结果类型
     * @throws Exception
     */
    public static<T> void writeExcel(HttpServletResponse response, List<T> data, String fileName, Class clazz) throws Exception {
        long exportStartTime = System.currentTimeMillis();
        log.info("报表导出Size: "+data.size()+"条。");

        List<List<T>> lists = SplitList.splitList(data,MAXROWS); // 分割的集合

        OutputStream out = getOutputStream(fileName, response);
        ExcelWriterBuilder excelWriterBuilder = EasyExcel.write(out, clazz).excelType(ExcelTypeEnum.XLSX).registerWriteHandler(getDefaultHorizontalCellStyleStrategy());
        ExcelWriter excelWriter = excelWriterBuilder.build();
        ExcelWriterSheetBuilder excelWriterSheetBuilder;
        WriteSheet writeSheet;
        for (int i =1;i<=lists.size();i++){
            excelWriterSheetBuilder = new ExcelWriterSheetBuilder(excelWriter);
            excelWriterSheetBuilder.sheetNo(i);
            excelWriterSheetBuilder.sheetName("sheet"+i);
            writeSheet = excelWriterSheetBuilder.build();
            excelWriter.write(lists.get(i-1),writeSheet);
        }
        out.flush();
        excelWriter.finish();
        out.close();
        System.out.println("报表导出结束时间:"+ new Date()+";写入耗时: "+(System.currentTimeMillis()-exportStartTime)+"ms" );
    }


    private static OutputStream getOutputStream(String fileName, HttpServletResponse response) throws Exception {
        fileName = URLEncoder.encode(fileName, "UTF-8");
        //  response.setContentType("application/vnd.ms-excel"); // .xls
        response.setContentType("application/vnd.openxmlformats-officedocument.spreadsheetml.sheet"); // .xlsx
        response.setCharacterEncoding("utf8");
        response.setHeader("Content-Disposition", "attachment;filename=" + fileName + ".xlsx");
        return response.getOutputStream();
    }


}

2. SplitList

java">package com.sinosoft.web.rest.util;



import java.util.ArrayList;
import java.util.Arrays;
import java.util.List;

public class SplitList {

    /**
     * update qy 2020-09-25
     * @param list 待切割集合
     * @param len 集合按照多大size来切割
     * @param <T>
     * @return
     */
    public static<T> List<List<T>> splitList(List<T> list, int len) {
        if (list == null || list.size() == 0 || len < 1) {
            return null;
        }
        List<List<T>> result = new ArrayList<List<T>>();
        int size = list.size();
        int count = (size + len - 1) / len;

        for (int i = 0; i < count; i++) {
            List<T> subList = list.subList(i * len, ((i + 1) * len > size ? size : len * (i + 1)));
            result.add(subList);
        }
        return result;
    }



    /**
     * @version add QY 2020-09-25
     * @description 集合平均分组
     * @param source 源集合
     * @param n      分成n个集合
     * @param <T>    集合类型
     * @return
     */
    public static <T> List<List<T>> groupList(List<T> source, int n) {
        if (source == null || source.size() == 0 || n < 1) {
            return null;
        }
        if (source.size() < n) {
            return Arrays.asList(source);
        }
        List<List<T>> result = new ArrayList<List<T>>();
        int number = source.size() / n;
        int remaider = source.size() % n;
        int offset = 0; // 偏移量，每有一个余数分配，就要往右偏移一位
        for (int i = 0; i < n; i++) {
            List<T> list1 = null;
            if (remaider > 0) {
                list1 = source.subList(i * number + offset , (i + 1) * number + offset + 1);
                remaider--;
                offset++;
            } else {
                list1 = source.subList(i * number + offset, (i + 1) * number + offset);
            }
            result.add(list1);
        }

        return result;
    }


}

• Resource/Controller 层

java"> // EasyExcel样例
    @PostMapping("/test/printByEasyExcel")
    public void printByEasyExcel(@RequestBody Map<String,Object> map, HttpServletResponse response) throws IOException {
       easyExcelService.printByEasyExcel(map,response);
    }

• Service层

java">public void printByEasyExcel(Map<String,Object> map, HttpServletResponse response) throws IOException {
        //查询要导出的明细信息
        List<?> modelList = easyExcelQueryService.queryResult(map);
        try {
            EasyExcelUtil.writeExcel(response, modelList, "导出的报表名称", PrintModel.class);
        } catch (Exception e) {
            e.printStackTrace();
        }
    }

• 打印映射的实体类

java">import com.alibaba.excel.annotation.ExcelProperty;
import com.alibaba.excel.annotation.write.style.ColumnWidth;
import com.alibaba.excel.annotation.write.style.ContentRowHeight;
import com.alibaba.excel.annotation.write.style.HeadRowHeight;
import lombok.*;

import java.io.Serializable;


@NoArgsConstructor
@AllArgsConstructor
@ContentRowHeight(15)
@HeadRowHeight(17)
public class PrintModel implements Serializable {

    @ColumnWidth(10)
    @ExcelProperty(value = "月份", index = 0)
    private String yearMonth;

    @ColumnWidth(10)
    @ExcelProperty(value = "销售渠道", index = 1)
    private String branchType;

    @ColumnWidth(15)
    @ExcelProperty(value = "保单号码", index = 2)
    private String mainPolNo;

    @ColumnWidth(15)
    @ExcelProperty(value = "承保日期", index = 3)
    private String signDate;

    @ColumnWidth(15)
    @ExcelProperty(value = "发生日期", index = 4)
    private String getPolDate;

    @ColumnWidth(15)
    @ExcelProperty(value = "代理人编号", index = 5)
    private String date;

    @ColumnWidth(10)
    @ExcelProperty(value = "代理人姓名", index = 6)
    private String doubleData;

    @ColumnWidth(15)
    @ExcelProperty(value = "保险产品代码", index = 7)
    private String riskCode;

    @ColumnWidth(10)
    @ExcelProperty(value = "金额", index = 8)
    private String fyc;

    @ColumnWidth(15)
    @ExcelProperty(value = "回机日期", index = 9)
    private String tMakeDate;

    @ColumnWidth(10)
    @ExcelProperty(value = "计佣年月", index = 10)
    private String statWageNo;

    @ColumnWidth(8)
    @ExcelProperty(value = "账龄日", index = 11)
    private String ageDay;

    @ColumnWidth(10)
    @ExcelProperty(value = "分公司代码", index = 12)
    private String branchName;

    public String getYearMonth() {
        return yearMonth;
    }

    public void setYearMonth(String yearMonth) {
        this.yearMonth = yearMonth;
    }

    public String getBranchType() {
        return branchType;
    }

    public void setBranchType(String branchType) {
        this.branchType = branchType;
    }

    public String getMainPolNo() {
        return mainPolNo;
    }

    public void setMainPolNo(String mainPolNo) {
        this.mainPolNo = mainPolNo;
    }

    public String getSignDate() {
        return signDate;
    }

    public void setSignDate(String signDate) {
        this.signDate = signDate;
    }

    public String getGetPolDate() {
        return getPolDate;
    }

    public void setGetPolDate(String getPolDate) {
        this.getPolDate = getPolDate;
    }

    public String getDate() {
        return date;
    }

    public void setDate(String date) {
        this.date = date;
    }

    public String getDoubleData() {
        return doubleData;
    }

    public void setDoubleData(String doubleData) {
        this.doubleData = doubleData;
    }

    public String getRiskCode() {
        return riskCode;
    }

    public void setRiskCode(String riskCode) {
        this.riskCode = riskCode;
    }

    public String getFyc() {
        return fyc;
    }

    public void setFyc(String fyc) {
        this.fyc = fyc;
    }

    public String gettMakeDate() {
        return tMakeDate;
    }

    public void settMakeDate(String tMakeDate) {
        this.tMakeDate = tMakeDate;
    }

    public String getStatWageNo() {
        return statWageNo;
    }

    public void setStatWageNo(String statWageNo) {
        this.statWageNo = statWageNo;
    }

    public String getAgeDay() {
        return ageDay;
    }

    public void setAgeDay(String ageDay) {
        this.ageDay = ageDay;
    }

    public String getBranchName() {
        return branchName;
    }

    public void setBranchName(String branchName) {
        this.branchName = branchName;
    }
}

小结

循环写了2500000数据，然后测试导出，导出三个Sheet页，写入耗时: 171873ms。报表 81.1 MB

所以建议业务上涉及大批量数据导出时，表头没必要弄得花里胡哨，效率为主。尽可能的使用EasyExcel来导出数据，使用Poi很容易在并发时导致内存溢出。当然，Poi在导出某些花里胡哨的报表，小批量数据导出时，还是很香的。
再啰嗦一句，像数据量很大很大的报表，在导出时，可以把内容的样式去了。Style非常占用空间，工具类EasyExcelUtil代码做出相应调整即可。