javascript - express中路由里面req.session是undefind

Question

最近在学习nodejs，看的是《nodejs开发指南》(有点老了)，遇到了一个问题，就是在注册页面输入密码和确认密码时，如果两个不相等，则将错误信息存到session中，在express2.X即原书中是利用req.flash API+动态视图助手来实现的，我用的是4.x，通过res.locals保存的。可是在路由中判断的时候通过req.session.error='密码不一致'的时候发生了错误

附上代码:
路由部分：

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

router.get('/', function (req, res) {
    res.render('index', {title: '首页'});
});

router.get('/reg', function (req, res) {
    res.render('reg', {title: '注册'})
});

router.post('/reg', function (req, res) {
    if (req.body['password-repeat'] != req.body['password']) {
        req.session.error = '两次输入的密码不一致';
        return res.redirect('/reg');
    }
});

module.exports = router;

app.js部分

var express = require('express');
var path = require('path');
var favicon = require('serve-favicon');
var logger = require('morgan');
var cookieParser = require('cookie-parser');
var bodyParser = require('body-parser');
var partials = require('express-partials');
var session = require('express-session');
var mongoStore = require('connect-mongo')(session);

var routes = require('./routes');
var setting = require('./setting');
var db = require('./db');

var app = express();

app.set('views', path.join(__dirname, 'views'));
app.set('view engine', 'ejs');
app.use(partials());

// uncomment after placing your favicon in /public
//app.use(favicon(path.join(__dirname, 'public', 'favicon.ico')));
app.use(logger('dev'));
app.use(bodyParser.json());
app.use(bodyParser.urlencoded({extended: false}));
app.use(cookieParser());

app.use('/', routes);
app.use(express.static(path.join(__dirname, 'public')));


app.use(session({
    secret: setting.cookieSecret,
    store: new mongoStore({
        mongooseConnection: db.dbCon
    })
}));


// catch 404 and forward to error handler
app.use(function (req, res, next) {
    var err = new Error('Not Found');
    err.status = 404;
    next(err);
});

app.use(function (req, res, next) {
    var err = req.session.error;
    var success = req.session.success;
    var user = req.session.user;
    var mess = req.session.message;
    delete req.session.success;
    delete  req.session.error;
    delete  req.session.message;
    if (err) {
        res.locals.err = "*" + err;
    }
    if (mess) {
        res.locals.message = "*" + mess;
    }
    if (success) {
        res.locals.success = success;
    }
    if (user) {
        res.locals.user = user.name;
    }
    next();
});

module.exports = app;

网上翻了很久，都没找到，这篇博文说http://blog.sina.com.cn/s/blo...需要把路由写在session的后面，可是按他那么做页面就Not Found了。这个问题困扰了我很久了，求大神解答，顺便求推荐一些新点express资源。感激不尽

Answer 1

肯定要把 app.use(session) 放在路由 app.use('/', routes) 的前面，不然 routes 里的中间件直接把请求处理了（甚至结束了请求），哪还有机会执行 session？即使后面执行了 session，也是在你处理请求之后，所以你处理请求的时候 req.session 必定啥也没有。

你把 app.use(session) 紧挨着放在 app.use('/', routes) 的上边，应该不会出现 Not Found的错误，如果有，再另外debug。