如果Express.js中使用了子路由器模块，我应该将中间件放在哪里

全部：

当我学习如何使用Express.js上传文件时，有一个称为multer（）的中间件，从其使用示例可以看出：

var express = require('express')
var multer  = require('multer')
var upload = multer({ dest: 'uploads/' })

var app = express()

app.post('/profile', upload.single('avatar'), function (req, res, next) {
  // req.file is the `avatar` file
  // req.body will hold the text fields, if there were any
})

app.post('/photos/upload', upload.array('photos', 12), function (req, res, next) {
  // req.files is array of `photos` files
  // req.body will contain the text fields, if there were any
})

var cpUpload = upload.fields([{ name: 'avatar', maxCount: 1 }, { name: 'gallery', maxCount: 8 }])
app.post('/cool-profile', cpUpload, function (req, res, next) {
  // req.files is an object (String -> Array) where fieldname is the key, and the value is array of files
  //
  // e.g.
  //  req.files['avatar'][0] -> File
  //  req.files['gallery'] -> Array
  //
  // req.body will contain the text fields, if there were any
})

app.js中直接使用的中间件对象，我想知道是否使用子路由器，如：

app.js

var routes = require('./routes/index');
app.use("/", routes);

var express = require('express');
var router = express.Router();

/* GET home page. */
router.get('/', function(req, res, next) {
  res.render('index', { title: 'Express' });
});

router.post('/upload', function(req, res, next) {
    debugger;
  console.log(req.body.upld);
  console.log(req.file);
  res.send("");
});


module.exports = router;

index.js

var routes = require('./routes/index');
app.use("/", routes);

var express = require('express');
var router = express.Router();

/* GET home page. */
router.get('/', function(req, res, next) {
  res.render('index', { title: 'Express' });
});

router.post('/upload', function(req, res, next) {
    debugger;
  console.log(req.body.upld);
  console.log(req.file);
  res.send("");
});


module.exports = router;

我想知道我应该把那个上传中间件放在哪里？我应该在每个文件中使用var upload=multer（{dest:'uploads/'}）吗？如果是，这是否会导致根据路由器文件在不同文件夹中生成多个上载文件夹

谢谢