1、 introduce poi rely on

    <dependency>
      <groupId>org.apache.poi</groupId>
      <artifactId>poi</artifactId>
      <version>3.15</version>
    </dependency>

2、 front end jsp page

        <span>
            <button id="exportActivityAllBtn"> export excel</button>
        </span>

js Code

$("#exportActivityAllBtn").click(function () {

        window.location.href="${pageContext.request.contextPath}/exportAllActivitys" ;

    });

3、controller Layer code

@RequestMapping("exportAllActivitys")
    public void exportAllActivitys(HttpServletResponse response) throws IOException {

        // call service Of findAll() Method to get data 
        // obtain service All data acquisition methods of layer 
        List<User> list = userService.findAll();
        // use apache Of poi establish excel file , And put list write in excel In file 
        // establish HSSFWorkbook object , Corresponding to one excel file 
        HSSFWorkbook wb = new HSSFWorkbook();
        // Use wb establish HSSFSheet object , Corresponding wb A page in a document 
        HSSFSheet sheet = wb.createSheet("user list ");// Set page name 
        // Use sheet establish HSSFRow object , Corresponding sheet A row in the 
        HSSFRow row = sheet.createRow(0);// The index for 0 It's the first line 
        // Use row establish HSSFCell object , Corresponding row Column in 
        HSSFCell cell = row.createCell(0);// The index for 0 That's the first column 


        // Set the value in the column 
        cell.setCellValue("id");
        cell=row.createCell(1);
        cell.setCellValue(" full name ");
        cell=row.createCell(2);
        cell.setCellValue(" account number ");
        cell=row.createCell(3);
        cell.setCellValue(" Gender ");
        cell=row.createCell(4);
        cell.setCellValue(" Date of birth ");
        cell=row.createCell(5);
        cell.setCellValue(" Department ");
        cell=row.createCell(6);
        cell.setCellValue(" state ");
        cell=row.createCell(7);

        // Traverse ActivityList, establish Row
        // First judge list There's no data 
        if(list!=null && list.size()>0){
            User user=null;//user If you get the external definition, you don't need to create it every time , More efficient 
            for (int i=0;i<list.size();i++){
                user=list.get(i);
                // Every time you traverse one user, Generate a line 
                row=sheet.createRow(i+1);
                cell = row.createCell(0);
                cell.setCellValue(user.getUserId());
                cell = row.createCell(1);
                cell.setCellValue(user.getUserName());
                cell = row.createCell(2);
                cell.setCellValue(user.getAccount());
                cell = row.createCell(3);
                cell.setCellValue(user.isGender());

                SimpleDateFormat simpleDateFormat = new SimpleDateFormat("yyyy-MM-dd");
                String birthDay = simpleDateFormat.format(user.getBirthDay());
                cell = row.createCell(4);
                cell.setCellValue(birthDay);

                cell = row.createCell(5);
                cell.setCellValue(user.getDept().getDeptName());
                cell = row.createCell(6);
                cell.setCellValue(user.getState());
            }
        }
        // After improvement ！！！！！！！！！！！！！！！！！！！！！

        // Set response type  application/octet-stream Express excel file 
        response.setContentType("application/octet-stream;charset=UTF-8");
        // Set the response header   Content-Disposition Open mode  attachment In the form of an attachment 
        response.addHeader("Content-Disposition","attachment;filename=userList.xls");
        OutputStream out = response.getOutputStream();
        wb.write(out);
        wb.close();
        out.flush();//out from response Generated ,tomcat Will close itself , You can't close it yourself , No flush Data may be lost 

    }