如何将 Java SocketIO 连接到 Javascript 服务器

Question

I have a javascript server server.js

const http = require("http").createServer()
const io = require("socket.io")(http)   

io.on("connection", socket => {
    console.log("a user connected")
})

http.listen(3000, () => {
    console.log("listening on *:3000")
})

and a java client SocketIO.java

package chess_client;

import java.net.URISyntaxException;

import io.socket.client.IO;
import io.socket.client.Socket;
import io.socket.emitter.Emitter;

public class SocketIO {
    private static Socket socket;

    public static void main(String[] args) throws URISyntaxException {
        socket = IO.socket("http://localhost:3000");

        socket.on(Socket.EVENT_CONNECT, new Emitter.Listener() {

            @Override
            public void call(Object... args) {
                System.out.println("Connected!");
            }

        });

        socket.connect();
    }
}

I've been searching for Javascript Server & Java Client examples but the example on https://github.com/socketio/socket.io-client-java only shows the Java Client example without the Javascript Server code. When combining both, nothing works. I don't see anything in either of the terminals when I run both codes??? What's wrong???
For any answers given, do note that I would prefer using Typescript than Javascript but both are acceptable

Answer 1

I've found my answer after the Java SocketIO client was updated. I made some mistakes.

1. I need the npm package for socket.io to be version 2.*
   The documentation stated that for a version of 1.* for the Java Client, the SocketIO server must be of version 2.* . At this time, 2.3.0 is the latest npm package for socket.io so install that instead of version 3.* .
2. I'm assuming the Java Client is of a different host because it's not rendered by the server itself. For example, this is the code on the official SocketIO documentation:

app.get('/', (req, res) => {
  res.sendFile(__dirname + '/index.html');
});

In this example, the Javascript server is directly rendering the HTML file so However, the Java code can't be run by a Javascript server.This is why when creating the const io , we should change it to:

const io =  require('socket.io')(http, {
    cors: { origin: '*' }
})

This allows code of any host - or origin - to access the SocketIO server.


Here's an example of my working Java Client and Javascript Server if anyone needs the reference
app.js :

const http = require('http').createServer()

const io =  require('socket.io')(http, {
    cors: { origin: '*' }
})

io.on('connection', (socket) => {
    console.log('Connected to client!')

    io.emit('time', Date.now())
})

http.listen(8080, () => console.log('Server running on port 8080'))

App.java :

package socket_test;

import java.net.URISyntaxException;

import io.socket.client.IO;
import io.socket.client.Socket;
import io.socket.emitter.Emitter;

public class App {
    public static void main(String[] args) throws URISyntaxException {
        Socket socket = IO.socket("http://localhost:8080");
        socket.on(Socket.EVENT_CONNECT, new Emitter.Listener() {

            @Override
            public void call(Object... args) {
                System.out.println("Connected to server!");
            }

        });
        socket.on("time", new Emitter.Listener() {
            
            @Override
            public void call(Object... args) {
                System.out.println("Time: " + args[0]);
            }
            
        });
        socket.connect();
    }
}