写在最前面：
　　　　使用的是JAVA POI实现的导出Excel；
　　　　POI 提供了对2003版本的Excel的支持 ---- HSSFWorkbook
　　　　POI 提供了对2007版本以及更高版本的支持 ---- XSSFWorkbook

引入相关依赖：

        <dependency><groupId>org.apache.poi</groupId><artifactId>poi-ooxml</artifactId><version>4.1.2</version></dependency>

/*** 读取Excel文件的内容* @param inputStream excel文件，以InputStream的形式传入* @param sheetName sheet名字* @return 以List返回excel中内容*/public static List<Map<String, String>> readExcel(InputStream inputStream, String sheetName) {//定义工作簿XSSFWorkbook xssfWorkbook = null;try {xssfWorkbook = new XSSFWorkbook(inputStream);} catch (Exception e) {System.out.println("Excel data file cannot be found!");}//定义工作表XSSFSheet xssfSheet;if (sheetName.equals("")) {// 默认取第一个子表xssfSheet = xssfWorkbook.getSheetAt(0);} else {xssfSheet = xssfWorkbook.getSheet(sheetName);}List<Map<String, String>> list = new ArrayList<Map<String, String>>();//定义行//默认第一行为标题行，index = 0XSSFRow titleRow = xssfSheet.getRow(0);//循环取每行的数据for (int rowIndex = 1; rowIndex < xssfSheet.getPhysicalNumberOfRows(); rowIndex++) {XSSFRow xssfRow = xssfSheet.getRow(rowIndex);if (xssfRow == null) {continue;}Map<String, String> map = new LinkedHashMap<String, String>();//循环取每个单元格(cell)的数据for (int cellIndex = 0; cellIndex < xssfRow.getPhysicalNumberOfCells(); cellIndex++) {XSSFCell titleCell = titleRow.getCell(cellIndex);XSSFCell xssfCell = xssfRow.getCell(cellIndex);map.put(getString(titleCell),getString(xssfCell));}list.add(map);}return list;}/*** 把单元格的内容转为字符串* @param xssfCell 单元格* @return 字符串*/public static String getString(XSSFCell xssfCell) {if (xssfCell == null) {return "";}if (xssfCell.getCellTypeEnum() == CellType.NUMERIC) {return String.valueOf(xssfCell.getNumericCellValue());} else if (xssfCell.getCellTypeEnum() == CellType.BOOLEAN) {return String.valueOf(xssfCell.getBooleanCellValue());} else {return xssfCell.getStringCellValue();}}/*** 把内容写入Excel* @param list 传入要写的内容，此处以一个List内容为例，先把要写的内容放到一个list中* @param outputStream 把输出流怼到要写入的Excel上，准备往里面写数据*/public static void writeExcel(List<List> list, OutputStream outputStream) {//创建工作簿XSSFWorkbook xssfWorkbook = null;xssfWorkbook = new XSSFWorkbook();//创建工作表XSSFSheet xssfSheet;xssfSheet = xssfWorkbook.createSheet();//创建行XSSFRow xssfRow;//创建列，即单元格CellXSSFCell xssfCell;//把List里面的数据写到excel中for (int i=0;i<list.size();i++) {//从第一行开始写入xssfRow = xssfSheet.createRow(i);//创建每个单元格Cell，即列的数据List sub_list =list.get(i);for (int j=0;j<sub_list.size();j++) {xssfCell = xssfRow.createCell(j); //创建单元格xssfCell.setCellValue((String)sub_list.get(j)); //设置单元格内容}}//用输出流写到exceltry {xssfWorkbook.write(outputStream);outputStream.flush();outputStream.close();}catch (IOException e) {e.printStackTrace();}}

附：把一个Map中的所有键和值分别放到一个list中，再把这两个list整个放到一个大的list里面，即 [ [key1,key2,key3…] , [value1,value2,value3…] ]

    public static List<List> convertMapToList(Map map) {List<List> list = new ArrayList<List>();List<String> key_list = new LinkedList<String>();List<String> value_list = new LinkedList<String>();Set<Entry<String,String>> set = map.entrySet();Iterator<Entry<String,String>> iter1 = set.iterator();while (iter1.hasNext()) {key_list.add(iter1.next().getKey());}list.add(key_list);Collection<String> value = map.values();Iterator<String> iter2 = value.iterator();while (iter2.hasNext()) {value_list.add(iter2.next());}list.add(value_list);return list;}

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导出接口：

package com.wqd.dove.demo.export.controller;import com.wqd.dove.demo.export.mapper.UserMapper;
import com.wqd.dove.demo.export.pojo.User;
import lombok.RequiredArgsConstructor;
import org.apache.poi.xssf.usermodel.XSSFCell;
import org.apache.poi.xssf.usermodel.XSSFRow;
import org.apache.poi.xssf.usermodel.XSSFSheet;
import org.apache.poi.xssf.usermodel.XSSFWorkbook;
import org.springframework.web.bind.annotation.GetMapping;
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.UnsupportedEncodingException;
import java.net.URLEncoder;
import java.util.List;/*** @author frank* @description 导出Excel文件控制器* @date 2021/12/18 14:06*/
@RestController
@RequiredArgsConstructor
@RequestMapping(value = {"/export"})
public class MyExcelExportController {private final UserMapper userMapper;@GetMapping(value = "/excel")public void exportExcel(HttpServletResponse response) throws UnsupportedEncodingException {List<User> list = userMapper.list();XSSFWorkbook workbook = new XSSFWorkbook();XSSFSheet sheet = workbook.createSheet();XSSFRow row0 = sheet.createRow(0);row0.createCell(0).setCellValue("姓名");row0.createCell(1).setCellValue("地址");row0.createCell(2).setCellValue("密码");row0.createCell(3).setCellValue("电话");for (int i = 0; i < list.size(); i++) {XSSFRow row = sheet.createRow(i + 1);XSSFCell cell = row.createCell(0);cell.setCellValue(list.get(i).getName());XSSFCell cell1 = row.createCell(1);cell1.setCellValue(list.get(i).getAddress());XSSFCell cell2 = row.createCell(2);cell2.setCellValue(list.get(i).getPassword());XSSFCell cell3 = row.createCell(3);cell3.setCellValue(list.get(i).getPhone());}response.setCharacterEncoding("UTF-8");//让服务器告诉浏览器它发送的数据属于什么文件类型response.setHeader("content-Type", "application/vnd.ms-excel");//当Content-Type 的类型为要下载的类型时 , 这个信息头会告诉浏览器这个文件的名字和类型。response.setHeader("Content-Disposition","attachment;filename=" + URLEncoder.encode("b.xlsx", "UTF-8"));try {workbook.write(response.getOutputStream());} catch (IOException e) {e.printStackTrace();}}}

访问接口：

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