当我为下面的代码制作GET http://localhost:8080/messages/3/sentiments时，为什么param方法被调用两次？那么，如果我有10条路线，它将被调用10次？
var comments = new Router();
comments.get('/comments', function (req, res, next) {
res.send('Comments by message_id=' + req.message._id);
})
var sentiments = new Router();
sentiments.get('/sentiments', function (req, res, next) {
res.send('Comments by message_id=' + req.message._id);
})
var messages = new Router();
messages.param('_message', function (req, res, next, _id) {
console.log("Set message");
fs.readFile(__filename, function () {
req.message = { _id: _id };
next();
});
})
messages.use('/messages/:_message/', comments);
messages.use('/messages/:_message/', sentiments);
app.use(messages);
app.listen(8080);