Java Server WebSockets JavaScript Client

Question

I am trying to establish a connection between a server in Java and a JavaScript client, but I get this error on the client side:

WebSocket connection failed with 'ws: //127.0.0.1: 4444 /': the connection is closed before receiving a handshake response

It may remain in OPENNING state because the connection.onopen function is never called. console.log('Connected!') is called.

Can someone let me know what is going wrong here?

server

 import java.io.IOException; import java.net.ServerSocket; public class Server { public static void main(String[] args) throws IOException { try (ServerSocket serverSocket = new ServerSocket(4444)) { GameProtocol gp = new GameProtocol(); ServerThread player= new ServerThread(serverSocket.accept(), gp); player.start(); } catch (IOException e) { System.out.println("Could not listen on port: 4444"); System.exit(-1); } } } 

Serverthread

 import java.io.BufferedReader; import java.io.IOException; import java.io.InputStreamReader; import java.io.PrintWriter; import java.net.Socket; public class ServerThread extends Thread{ private Socket socket = null; private GameProtocol gp; public ServerThread(Socket socket, GameProtocol gp) { super("ServerThread"); this.socket = socket; this.gp = gp; } public void run() { try ( PrintWriter out = new PrintWriter(socket.getOutputStream(), true); BufferedReader in = new BufferedReader( new InputStreamReader( socket.getInputStream())); ) { String inputLine, outputLine; while ((inputLine = in.readLine()) != null) { outputLine = gp.processInput(inputLine); System.out.println(outputLine); } socket.close(); } catch (IOException e) { e.printStackTrace(); } } } 

Gameprotocol

 public class GameProtocol { public String processInput(String theInput) { String theOutput = null; theOutput = theInput; return theOutput; } } 

customer

 var connection = new WebSocket('ws://127.0.0.1:4444'); connection.onopen = function () { console.log('Connected!'); connection.send('Ping'); // Send the message 'Ping' to the server }; // Log errors connection.onerror = function (error) { console.log('WebSocket Error ' + error); }; // Log messages from the server connection.onmessage = function (e) { console.log('Server: ' + e.data); }; 

Answer 1

To begin with, your code looks identical to Java and JavaScript code. Both work for what they are intended for, but the fact is that you are trying to connect a WebSocket client to a socket server.

As far as I know, these are two different things regarding this answer .

I never tried it your way. However, if I have a network application that uses a socket, then it would be a clean client / server socket, and if it were a web application, I would also use WebSocket on both sides.

So far, so good..

To do this, this answer suggests using any available WebSocket on the server side, and your problem is solved.

I am using WebSocket for Java, and here is an example implementation that I tested with your client code, and it works both on the client side and the server side.

 import org.java_websocket.WebSocket; import org.java_websocket.handshake.ClientHandshake; import org.java_websocket.server.WebSocketServer; import java.net.InetSocketAddress; import java.util.HashSet; import java.util.Set; public class WebsocketServer extends WebSocketServer { private static int TCP_PORT = 4444; private Set<WebSocket> conns; public WebsocketServer() { super(new InetSocketAddress(TCP_PORT)); conns = new HashSet<>(); } @Override public void onOpen(WebSocket conn, ClientHandshake handshake) { conns.add(conn); System.out.println("New connection from " + conn.getRemoteSocketAddress().getAddress().getHostAddress()); } @Override public void onClose(WebSocket conn, int code, String reason, boolean remote) { conns.remove(conn); System.out.println("Closed connection to " + conn.getRemoteSocketAddress().getAddress().getHostAddress()); } @Override public void onMessage(WebSocket conn, String message) { System.out.println("Message from client: " + message); for (WebSocket sock : conns) { sock.send(message); } } @Override public void onError(WebSocket conn, Exception ex) { //ex.printStackTrace(); if (conn != null) { conns.remove(conn); // do some thing if required } System.out.println("ERROR from " + conn.getRemoteSocketAddress().getAddress().getHostAddress()); } } 

According to your main method, just:

 new WebsocketServer().start(); 

You may need to manipulate your code to fit this implementation, but this should be part of the job.

Here is the test result with 2 tests:

 New connection from 127.0.0.1 Message from client: Ping Closed connection to 127.0.0.1 New connection from 127.0.0.1 Message from client: Ping 

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Here is the WebSocket maven configuration, otherwise upload the JAR file / s manually and import them into your development / development environment:

 <!-- https://mvnrepository.com/artifact/org.java-websocket/Java-WebSocket --> <dependency> <groupId>org.java-websocket</groupId> <artifactId>Java-WebSocket</artifactId> <version>1.3.0</version> </dependency> 

Link to WebSocket .