req.body获取不到post数据？

express -V === 4.13.4 app.js code: var express = require("express");
var bodyParser = require("body-parser");
var app = express();

app.use(bodyParser.urlencoded({ extended: false }));

app.post('/login',function(req,res){
var user_name=req.body.user;
var password=req.body.password;
console.log("User name = "+user_name+", password is "+password);
res.end("yes");
});

app.listen(3000);

postman请求返回： User name = undefined, password is undefined

请问大神这是怎么回事？