如何在 node.js 中运行子进程时首先完成加载答案

【问题标题】：How to finish loading first while child process is running in node.js如何在 node.js 中运行子进程时首先完成加载
【发布时间】：2019-04-22 09:34:24
【问题描述】：

我对 node.js 很陌生。目前，当我评估http://localhost:4000/testjar 时，我运行一个子进程来执行 jar 文件。加载页面并在子进程完成运行后显示标准输出需要一些时间。

有没有办法在等待子进程运行时先完成页面的加载，然后在子进程完成运行后将响应发送给客户端。因为我不希望页面加载这么久。

现在流程是

    browser loading -> start child process -> wait child process 
-> child process finish ->server send response -> browser finish loading

有没有类似

browser loading -> start child process -> browser finish loading and display pending for output 
-> wait child process -> child process finish ->server send response

这是我的 testjar.js

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

router.get('/', function(req, res, next) {      
    var exec = require('child_process').exec, child;

    child = exec('java -jar /home/java/testinput.jar',
        function (error, stdout, stderr){
            console.log('stdout: ' + stdout);
            console.log('stderr: ' + stderr);
            res.send(stdout);

            if(error !== null){
                console.log('exec error: ' + error);
            }
    });
});

module.exports = router;

【问题讨论】：

标签： javascript node.js express server child-process

【解决方案1】：

您可以为此使用socket.io：

npm install --save socket.io

app.js:

const express = require('express');
const app = express();
const server = require('http').Server(app);
const io = require('socket.io')(server);

app.use(express.static('public'));

function startProcess(callback) {
    setTimeout(function() {
        callback("I am done!");
    }, 3000);
    /*
    var exec = require('child_process').exec, child;
    child = exec('java -jar /home/java/testinput.jar',
        function (error, stdout, stderr) {
            console.log('stdout: ' + stdout);
            console.log('stderr: ' + stderr);
            callback(stdout);
            if (error !== null) {
                console.log('exec error: ' + error);
            }
        }
    );
    */
}

app.get('/start_process', function(req, res){
    console.log("got start_process request from socketId = " + req.query.socketId);
    io.to(req.query.socketId).emit('message', "process started");
    startProcess(function(message) {
        console.log('process finished, send message');
        io.to(req.query.socketId).emit('message', message);
    });  
    res.send('OK');
});

io.on('connection', function(socket){
    console.log('socket.io connected');
    socket.on('disconnect', function(){
        console.log('socket.io disconnected');
    });
});

server.listen(3000, function() {
    console.log('listening on *:3000');
});

public/index.html:

<!doctype html>
<html>
  <head>
    <title>Socket.IO Demo</title>
  </head>
  <body>
    <button id="startButton">start process</button>
    <div id="response"></div>
    <script src="/socket.io/socket.io.js"></script>
    <script>
        var socket = io();
        socket.on('message', function(message){
            console.log('process finished: ', message);
            document.getElementById("response").innerHTML = message;
        });
        document.getElementById("startButton").addEventListener("click", function(event) {
            var req = new XMLHttpRequest();
            req.onload = function() {
                console.log(req.response)
            };
            req.open("GET", "/start_process?socketId=" + socket.id);
            req.send();
        });
    </script>
  </body>
</html>

【讨论】：