文件下载的后端实现

代码实现：

package com.woniu.controller;

import com.baomidou.mybatisplus.extension.plugins.pagination.Page;
import com.woniu.bean.Subject;
import com.woniu.service.ISubjectService;
import org.apache.poi.hssf.usermodel.HSSFWorkbook;
import org.apache.poi.ss.usermodel.Row;
import org.apache.poi.ss.usermodel.Sheet;
import org.apache.poi.ss.usermodel.Workbook;
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.web.bind.annotation.*;

import javax.servlet.ServletOutputStream;
import javax.servlet.http.HttpServletResponse;
import java.io.IOException;
import java.util.List;


@CrossOrigin
@RestController
@RequestMapping("/POI")
public class POIController {


    @Autowired
    ISubjectService subjectService;

    @GetMapping("excel")
    public void sendExcel(Integer currentPage, Integer pageSize, String userName, HttpServletResponse response) throws IOException {

        Workbook wb = new HSSFWorkbook();
        // 准备分页数据
        Page ap = new Page<>(currentPage, pageSize);
        Page subjectPage = subjectService.page(ap);
        List subjects = subjectPage.getRecords();

        // 创建学科表
        Sheet sheet = wb.createSheet("学科");

        // 定义第一行数据
        Row row = sheet.createRow(0);
        row.createCell(0).setCellValue("id");
        row.createCell(1).setCellValue("学科名称");
        row.createCell(2).setCellValue("年级");

        Integer i=1;
        for (Subject subject : subjects) {
            Row r = sheet.createRow(i);
            r.createCell(0).setCellValue(subject.getId());
            r.createCell(1).setCellValue(subject.getName());
            r.createCell(2).setCellValue(subject.getLevelName());
            i++;
        }

        response.setHeader("content-disposition","attachment;filename=user.xls");


        ServletOutputStream os = response.getOutputStream();


        wb.write(os);


    }

}

解析：