在axios / react中发出发布请求时获取空数据作为响应

Question

Axios请求

handleUpload = e => {
    e.preventDefault();
    let files = this.state;
    console.log(files);
    let formdata = new FormData();
    //for(var x = 0; x<files.length; x++) {
    formdata.append("file", files);
    //}

    for (var key of formdata.entries()) {
      console.log(key[0] + ", " + key[1]);
    }

    const config = {
      headers: {
        "Content-Type": "application/x-www-form-urlencoded",
        Accept: "application/json"
      }
    };
    axios
      .post(
        "http://localhost:8081/api/uploadMultipleCsvFiles",
        formdata,
        config
        // headers: {'Content-Type': 'application/x-www-form-urlencoded'}
      )
      .then(res => console.log(res))
      .catch(err => console.log(err));
  };

这是回应

{data: "", status: 200, statusText: "OK", headers: {…}, config: {…}, …}
config: {url: "http://localhost:8081/api/uploadMultipleCsvFiles", method: "post", data: FormData, headers: {…}, transformRequest: Array(1), …}
data: ""
headers: {content-length: "0"}
request: XMLHttpRequest {readyState: 4, timeout: 0, withCredentials: false, upload: XMLHttpRequestUpload, onreadystatechange: ƒ, …}
status: 200
statusText: "OK"
__proto__: Object

server.js文件

const express = require('express')
const bodyParser= require('body-parser')
const multer = require('multer');
var cors = require('cors')
const app = express();
app.use(bodyParser.json())
app.use(cors())

//CREATE EXPRESS APP

var storage = multer.diskStorage({
  destination: function (req, file, cb) {
  cb(null, 'uploads')
},
filename: function (req, file, cb) {
  cb(null, Date.now() + '-' +file.originalname )
}
})
  var upload = multer({ storage: storage }).single('file')
//ROUTES WILL GO HERE
app.get('/', function(req, res) {
    res.sendFile(__dirname + '/index.html');  
});

app.post('/api/uploadMultipleCsvFiles', function(req, res) {
     console.log(req.body)
  upload(req, res, function (err) {
         if (err instanceof multer.MulterError) {
             return res.status(500).json(err)
         } else if (err) {
             return res.status(500).json(err)
         }
    return res.status(200).send(req.file)

  })

})

app.listen(8081, () => console.log('Server started on port 8081'));