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Is there any way to implement real time messaging web application (Push message to the client among multiple clients)? [duplicate]

I'm working on setting up my first websocket server for a communications app. I can't seem to figure out how websockets are implemented in Java.
I've tried, unsuccessfully, creating an annotation based Endpoint, but I'm not sure where the client info is going to come through. This is basically the gist of my code, without going into mundane details.
I'm trying to make the class MessageHelper deal with the websocket info transfer, I just can't grasp how to actually get the transfer there.
class MainServer implements Runnable {
// VARIABLES
ServerSocket serverSocket = null;
int port;
// CONSTRUCTORS
MainServer(int p) {
this.port = p;
}
// METHODS
public void run() {
openServerSocket();
while(!isStopped()){
try{
clientSocket = serverSocket.accept();
} catch(IOException e) {
// Do something
}
new Thread(new MainThread(clientSocket)).start();
}
}
}
// Other methods below.
public class MainThread {
final Socket socket;
MainThread(Socket s) {
this.socket = s;
}
public void run() {
try{
BufferedReader br = new BufferedReader(
new InputStreamReader(socket.getInputStream()));
String input = br.readLine(), read = br.readLine();
while(!input.isEmpty()) {
read += "\n";
read += input;
input = br.readLine();
}
/**
* Everything works fine, I'm just not sure where to go
* from here. I tried creating MessageHelper into the java
* websocket implementation using annotations but it did not
* accept input from the client after the handshake was
* made. My client would send something but it would just
* give and EOFException.
**/
if(websocketHandshakeRequest(read)) {
MessageHelper messageHelper =
new MessageHelper(this.socket);
} else {
// Do something
}
} catch(Exception e) {
// Do something.
}
}
}

Don't be confused about the name WebSocket. A TCP socket and a WebSocket are entirely different kind of "sockets".
In Java you use a ServerSocket for TCP sockets. TCP is a transport layer protocol used to implement application layer protocols like POP3 and HTTP.
WebSocket is a HTTP/1.1 protocol upgrade commonly used in web servers and web browsers. You cannot use a ServerSocket for the WebSocket protocol, at least not so straight forward as you might think. First, you have to implement the HTTP/1.1 protocol and then the WebSocket protocol on top of that.
In the Java world you can use web servers like Tomcat or Jetty which provide WebSocket implementations and a high level Java API. This API is part of the Jave Enterprise Edition (JEE). See also the Jave EE 7 Tutorial - Chapter 18 Java API for WebSocket.
E.g. Jetty is a lightweight JEE web server which can be embedded in your application or run as a stand-alone server. See Jetty Development Guide - Chapter 26. WebSocket Introduction.
So in a Java web application running in a WebSocket enabled JEE web server like Jetty you can implement a server side WebSocket as follows:
package com.example.websocket;
import org.apache.log4j.Logger;
import javax.websocket.CloseReason;
import javax.websocket.OnClose;
import javax.websocket.OnError;
import javax.websocket.OnMessage;
import javax.websocket.OnOpen;
import javax.websocket.Session;
import javax.websocket.server.ServerEndpoint;
import java.io.IOException;
#ServerEndpoint("/toUpper")
public class ToUpperWebsocket {
private static final Logger LOGGER = Logger.getLogger(ToUpperWebsocket.class);
#OnOpen
public void onOpen(Session session) {
LOGGER.debug(String.format("WebSocket opened: %s", session.getId()));
}
#OnMessage
public void onMessage(String txt, Session session) throws IOException {
LOGGER.debug(String.format("Message received: %s", txt));
session.getBasicRemote().sendText(txt.toUpperCase());
}
#OnClose
public void onClose(CloseReason reason, Session session) {
LOGGER.debug(String.format("Closing a WebSocket (%s) due to %s", session.getId(), reason.getReasonPhrase()));
}
#OnError
public void onError(Session session, Throwable t) {
LOGGER.error(String.format("Error in WebSocket session %s%n", session == null ? "null" : session.getId()), t);
}
}
You register your class as a WebSocket handler for the specific path with the #ServerEndpoint annotation. Your WebSocket URL is then ws://host:port/context/toUpper or wss://host:port/context/toUpper for HTTPS connections.
Edit:
Here is a very simplistic HTML page to demonstrate the client side connection to the above WebSocket. This page is served by the same webserver as the WebSocket. The webapplication containing the WebSocket is deployed at context "websocket" on localhost port 7777.
<html>
<body>
<h2>WebSocket Test</h2>
<div>
<input type="text" id="input" />
</div>
<div>
<input type="button" id="connectBtn" value="CONNECT" onclick="connect()" />
<input type="button" id="sendBtn" value="SEND" onclick="send()" disable="true" />
</div>
<div id="output">
<h2>Output</h2>
</div>
</body>
<script type="text/javascript">
var webSocket;
var output = document.getElementById("output");
var connectBtn = document.getElementById("connectBtn");
var sendBtn = document.getElementById("sendBtn");
var wsUrl = (location.protocol == "https:" ? "wss://" : "ws://") + location.hostname + (location.port ? ':'+location.port: '') + "/websocket/toUpper";
function connect() {
// open the connection if one does not exist
if (webSocket !== undefined
&& webSocket.readyState !== WebSocket.CLOSED) {
return;
}
updateOutput("Trying to establish a WebSocket connection to <code>" + wsUrl + "</code>");
// Create a websocket
webSocket = new WebSocket(wsUrl);
webSocket.onopen = function(event) {
updateOutput("Connected!");
connectBtn.disabled = true;
sendBtn.disabled = false;
};
webSocket.onmessage = function(event) {
updateOutput(event.data);
};
webSocket.onclose = function(event) {
updateOutput("Connection Closed");
connectBtn.disabled = false;
sendBtn.disabled = true;
};
}
function send() {
var text = document.getElementById("input").value;
webSocket.send(text);
}
function closeSocket() {
webSocket.close();
}
function updateOutput(text) {
output.innerHTML += "<br/>" + text;
}
</script>
</html>

If you're willing to use Java Spring - which I think would be great for your use case, it's pretty easy to setup a websocket server and client connection.
There's an example here - https://spring.io/guides/gs/messaging-stomp-websocket/

How to send message from node.js server to Android app?

Im trying to make a simple application. That is When I write a word at edittext in android app such as "Hi", Then android app send message "Hi" to node.js server and node.js server send message "Hi has sent successflly" to android app. This is just a example, actually my object is android send a data(message) to server, and receive another data(message) from server.
The problem is this. When I write a word at android app and press button, the message transmitted successfully(I can confirm by console at node.js). But I cant send message to android from node.js .. When I press send button, My android app shut down..
What android says is "java.lang.NullPointerException: Attempt to invoke virtual method 'void android.app.Activity.runOnUiThread(java.lang.Runnable)' on a null object reference" ..
Yesterday, this error didn't happened and another error occured. "cannot cast string to JSONObject."
I will show you my code.
Server Side(Node.js)
var app = require('express')();
var http = require('http').Server(app);
var io = require('socket.io')(http);
var port = 12000;
app.get('/', function(req, res) {
res.sendFile('index.html');
})
io.on('connection', function(socket) {
console.log('Android device has been connected');
socket.on('message', function(data) {
console.log('message from Android : ' + data);
Object.keys(io.sockets.sockets);
Object.keys(io.sockets.sockets).forEach(function (id) {
console.log("ID : ", id );
io.to(id).emit('message', data);
console.log(data + ' has sent successfully');
})
/*if (data != null) {
io.emit('message', {message : data + ' has received successfully'});
}*/
})
socket.on('disconnect', function() {
console.log('Android device has been disconnected');
})
})
http.listen(port, function() {
console.log('Server Start at port number ' + port);
})
Client Side (Android)
private Emitter.Listener handleIncomingMessages = new Emitter.Listener(){
#Override
public void call(final Object... args){
getActivity().runOnUiThread(new Runnable() {
#Override
public void run() {
JSONObject data = (JSONObject) args[0];
String message;
try {
message = data.getString("text").toString();
Log.i("result", message);
addMessage(message);
} catch (JSONException e) {
Log.e("result", "Error : JSONException");
return;
} catch (ClassCastException e) {
Log.e("result", "Error : ClassCastException");
e.printStackTrace();
return;
}
}
});
}
};
private void sendMessage(){
String message = mInputMessageView.getText().toString().trim();
mInputMessageView.setText("");
addMessage(message);
JSONObject sendText = new JSONObject();
try{
sendText.put("text", message);
socket.emit("message", message);
}catch(JSONException e){
}
}
private void addMessage(String message) {
mMessages.add(new Message.Builder(Message.TYPE_MESSAGE)
.message(message).build());
// mAdapter = new MessageAdapter(mMessages);
mAdapter = new MessageAdapter( mMessages);
mAdapter.notifyItemInserted(0);
scrollToBottom();
}
private void scrollToBottom() {
mMessagesView.scrollToPosition(mAdapter.getItemCount() - 1);
}
I already searched similar problems that other people asked, but It didn't give me solution. Please help me. Thank you for reading long question.
p.s Because Im not English speaker, Im not good at English .. There will be many problems at grammar and writing skills. Thanks for understanding...

Reason this happens is because method getActivity() returns null. This might happen if you run this on a fragment after it is detached from an activity or activity is no longer visible. I would do a normal null check before like:
Activity activity = getActivity();
if(activity != null) {
activity.runOnUiThread(new Runnable() {...}
}
I'm not familiar with socket.emit() method but it might throw network exception since it's running on UI thread and you are not allowed to do that. I recommend using RxJava/RxAndroid if you want to do this on another thread.
If you want to do network operation just use it like this:
Observable
.fromRunnable(new Runnable {
void run() {
// here do your work
}
})
.subscribeOn(Schedulers.newThread())
.observeOn(AndroidSchedulers.mainThread())
.subscribe(new Subscriber<Void>() {
#Override
public void onCompleted() {
// not really needed here
}
#Override
public void onError(Throwable e) {
// handle errors on UI thread
}
#Override
public void onNext(Void void) {
// do something on UI thread after run is done
}
});
Basically what it does it calls method call from Callable you just made on separate thread and when it's over it invokes onNext method if no exception was thrown or onError method if exception was thrown from Subscriber class.
Note that Response class isn't part of the RxJava/RxAndroid API and you can make it if you want. You can make it a simple POJO class or anything else you need it to be. If you don't need to have response you can use Runnable instead of Callable and it will work just fine.
In order for this to work you need to add this dependencies to your modules Gradle file:
dependencies {
compile 'io.reactivex:rxandroid:1.2.1'
compile 'io.reactivex:rxjava:1.1.6'
}

WebSocket - Invalid status line javascript

I'm running a spring 3.1.2 backend on a weblogic 12.1.3 server.
In order to accept websocket connections, my configurator as follows:
public class SpringConfigurator extends Configurator {
private static final Logger LOGGER = LoggerFactory.make();
private static final Map<String, Map<Class<?>, String>> cache = new ConcurrentHashMap<String, Map<Class<?>, String>>();
private static final String MAGIC_STR = "258EAFA5-E914-47DA-95CA-C5AB0DC85B11";
private static final String NO_VALUE = ObjectUtils.identityToString(new Object());
#SuppressWarnings("unchecked")
#Override
public <T> T getEndpointInstance(Class<T> endpointClass) throws InstantiationException {
WebApplicationContext wac = ContextLoader.getCurrentWebApplicationContext();
if (wac == null) {
String message = "Failed to find the root WebApplicationContext. Was ContextLoaderListener not used?";
LOGGER.error(message);
throw new IllegalStateException(message);
}
String beanName = ClassUtils.getShortNameAsProperty(endpointClass);
if (wac.containsBean(beanName)) {
T endpoint = wac.getBean(beanName, endpointClass);
if (LOGGER.isTraceEnabled()) {
LOGGER.trace("Using #ServerEndpoint singleton " + endpoint);
}
return endpoint;
}
Component annot = AnnotationUtils.findAnnotation(endpointClass, Component.class);
if ((annot != null) && wac.containsBean(annot.value())) {
T endpoint = wac.getBean(annot.value(), endpointClass);
if (LOGGER.isTraceEnabled()) {
LOGGER.trace("Using #ServerEndpoint singleton " + endpoint);
}
return endpoint;
}
beanName = getBeanNameByType(wac, endpointClass);
if (beanName != null) {
return (T) wac.getBean(beanName);
}
if (LOGGER.isTraceEnabled()) {
LOGGER.trace("Creating new #ServerEndpoint instance of type " + endpointClass);
}
return wac.getAutowireCapableBeanFactory().createBean(endpointClass);
}
// modifyHandshake() is called before getEndpointInstance()
#Override
public void modifyHandshake(ServerEndpointConfig sec, HandshakeRequest request, HandshakeResponse response) {
super.modifyHandshake(sec, request, response);
}
private String getBeanNameByType(WebApplicationContext wac, Class<?> endpointClass) {
String wacId = wac.getId();
Map<Class<?>, String> beanNamesByType = cache.get(wacId);
if (beanNamesByType == null) {
beanNamesByType = new ConcurrentHashMap<Class<?>, String>();
cache.put(wacId, beanNamesByType);
}
if (!beanNamesByType.containsKey(endpointClass)) {
String[] names = wac.getBeanNamesForType(endpointClass);
if (names.length == 1) {
beanNamesByType.put(endpointClass, names[0]);
} else {
beanNamesByType.put(endpointClass, NO_VALUE);
if (names.length > 1) {
String message = "Found multiple #ServerEndpoint's of type " + endpointClass + ", names=" + names;
LOGGER.error(message);
throw new IllegalStateException(message);
}
}
}
String beanName = beanNamesByType.get(endpointClass);
return NO_VALUE.equals(beanName) ? null : beanName;
}
}
The problem is when I try to open websocket connection via a javascript client, it correctly generates response headers as I debugged this location:
#Override
public void modifyHandshake(ServerEndpointConfig sec, HandshakeRequest request, HandshakeResponse response) {
super.modifyHandshake(sec, request, response);
}
But in client side it gives following error:
WebSocket connection to 'ws://localhost:7001/websocket' failed: Error during >WebSocket handshake: Invalid status line
In chrome developer tools the response seems as follows:
HTTP/0.9 200 OK
I think somehow http request does not upgrade to websocket connection.
I really appreciate any help regarding this issue.

I encountered exactly this issue today when testing http://showcase.omnifaces.org/push/socket on WebLogic 12.2.1.
Already at the first test attempt of the webapp, WebLogic throws the below exception when making a websocket connection:
java.lang.IllegalStateException: The async-support is disabled on this request: weblogic.servlet.internal.ServletRequest
Impl#6682044b[GET /omnifaces.push/counter?e6845a3a-26ed-4520-9824-63ffd85b24eb HTTP/1.1]
at weblogic.servlet.internal.ServletRequestImpl.startAsync(ServletRequestImpl.java:1949)
at weblogic.servlet.internal.ServletRequestImpl.startAsync(ServletRequestImpl.java:1925)
at javax.servlet.ServletRequestWrapper.startAsync(ServletRequestWrapper.java:432)
at weblogic.websocket.tyrus.TyrusServletFilter.doFilter(TyrusServletFilter.java:234)
...
It turns out that, on contrary to all other servers I tested, WebLogic's own TyrusServletFilter, which is responsible for handling websocket handshake requests, is internally installed after the filters provided via web.xml of the deployed webapp. The webapp shipped with a character encoding filter and a GZIP filter mapped on /*, so they were invoked before the websocket filter. This was strange at first sight, but I thought it is what it is, so I just added <async-supported>true</async-supported> to those webapp-provided filters so that the TyrusServletFilter can do its job.
However, when making a websocket connection, a JavaScript error in the client side occurred when a push message was being sent, exactly the one you faced:
WebSocket connection to 'ws://localhost:7001/omnifaces.push/counter?e6845a3a-26ed-4520-9824-63ffd85b24eb' failed: Error during WebSocket handshake: Invalid status line
It turns out that WebSockets just can't deal with GZIP responses. After disabling the GZIP filter, everything continued to work flawlessly.
The root problem is however that WebLogic should have installed its TyrusServletFilter before all webapp-provided filters. All other Java EE servers I ever have tested do this correctly. Your workaround of immediately dispatching and forwarding all websocket handshake requests to their target URL pattern, as mentioned in your comment on the question, is a good one. The alternative would be to reconfigure the web.xml-provided filters to not match websocket handshake requests anymore, e.g. by using a more specific URL pattern, or mapping to a specific servlet instead.

How to define Spring WebSocket subscriber path

I want to know how to define the subscriber path.
For instance, declaration of subscribing path
stompClient.subscribe("/topic/simplemessagesresponse", function(servermessage) {
Why there are two parts 'topic' and 'simplemessageresponse' .. what they refere. How many such domain parts can be there and why ? My question is on not only for the client side, but also server side . SimpMessagingTemplate.convertAndSend("/topic/simplemessagesresponse", "Message to client");
There are tutorials showing the websocket server and client samples. But no enough details of rules to declare the subscriber path and how the subscriber path could be found.
What are the dependencies to change the path when it is declared in server and client side. I think another similar question is raised because of the a location change of a page where the websocket client is written.

Quoting the STOMP spec documentation:
Note that STOMP treats this destination as an opaque string and no
delivery semantics are assumed by the name of a destination. You
should consult your STOMP server's documentation to find out how to
construct a destination name which gives you the delivery semantics
that your application needs.
That means that destination semantics is broker specific:
For RabbitMQ: check out the Destinations section under the STOMP
plugin documentation- http://www.rabbitmq.com/stomp.html For
For ActiveMQ: check out the Working with Destinations with Stomp -
https://activemq.apache.org/stomp.html

I have implemented the websocket stomp by following this blog.
I replaced #SendTo by SimpMessagingTemplate.
Here is my sample ChatController
#Autowired
private SimpMessagingTemplate simpMessagingTemplate;
#MessageMapping("/dualchart")
#ResponseBody
public void dualchat(MessageDTO message) {
// forward message to destination
String destination = "/topic/dualchat/" + message.getToUser();
simpMessagingTemplate.convertAndSend(destination, message);
}
MessageDTO
#JsonIgnoreProperties
public class MessageDTO extends BaseModel {
private String fromUser;
private String toUser;
private String message;
public String getFromUser() {
return fromUser;
}
public void setFromUser(String fromUser) {
this.fromUser = fromUser;
}
public String getToUser() {
return toUser;
}
public void setToUser(String toUser) {
this.toUser = toUser;
}
public String getMessage() {
return message;
}
public void setMessage(String message) {
this.message = message;
}
}
Web Socket Config
<websocket:message-broker application-destination-prefix="/app">
<websocket:stomp-endpoint path="/dualchat">
<websocket:sockjs />
</websocket:stomp-endpoint>
<websocket:simple-broker prefix="/topic" />
</websocket:message-broker>
Javascript
var socket = new SockJS("/starter.web.admin/dualchat");
var stompClient = Stomp.over(page.socket);
stompClient.connect({}, socketJsConnectedCallback, socketJsErrorCallback);
function socketJsConnectedCallback() {
var myId = "111"; // replace this Id
stompClient.subscribe('/topic/dualchat/' + myId, function(message) {
console.log("you reveived a message::::::::::" + JSON.stringify(message));
// you have message, and you can do anything with it
});
}
function socketJsErrorCallback(error){console.log(error);}
function sendMessage(message) {
var data = {
toUser : "1",
message : message
}
stompClient.send("/app/dualchat", {}, JSON.stringify(data );
}
Hope this will help next search...

Winsock.SendData equivalent with Javascript?

Can the following VB Script to open an IP cash drawer be done in Javascript instead?
Private Sub CashDrawerConnect_Click()
Winsock1.Close
ipaddr = "192.168.2.5"
Winsock1.RemoteHost = ipaddr
Winsock1.RemotePort = 30998
Winsock1.Connect
Sleep 250
TxtOpStatus = "Connection to the cash drawer at " & ipaddr & " is established..."
TxtOpStatus.Refresh
End Sub
Private Sub CashDrawerOpen_Click()
If Winsock1.State = sckConnected Then
Winsock1.SendData "opendrawer\0a"
Else
TxtOpStatus = "Not connected to the device"
TxtOpStatus.Refresh
End If
End Sub

You could do it on javascript, but not while running on a browser.
You would need to install nodejs and run your js file directly from the console.
This is a small example that would connect you the the drawer and send the "opendrawer" command on your example:
var net = require('net');
var client = net.connect({port: 30998, host: "yourip"}, function() {
client.write("opendrawer\0a");
});
If however the server has access to the drawer the javascript code could just make a request to the server which would be on charge of opening the connection to the drawer and sending the payload (opendrawer).
If you use php you can take a look at the sockets documentation.

Using VB and JavaScript the calls are mostly the same, you just jhave to adapt it to the language. http://www.ostrosoft.com/oswinsck/oswinsck_javascript.asp
The following is a snippet that uses WinSock from JScript
var oWinsock;
var sServer = "192.168.2.5";
var nPort = 3098;
var bClose = false;
oWinsock = new ActiveXObject("OSWINSCK.Winsock");
// Hooking up handlers
WScript.ConnectObject(oWinsock, "oWinsock_");
oWinsock.Connect(sServer, nPort);
WScript.Echo("Invalid URL");
bClose = true;
function oWinsock_OnConnect() {
oWinsock.SendData('Your data');
}
function oWinsock_OnDataArrival(bytesTotal) {
var sBuffer = oWinsock.GetDataBuffer();
sSource = sSource + sBuffer;
}
function oWinsock_OnError(Number, Description, Scode, Source,
HelpFile, HelpContext, CancelDisplay) {
WScript.Echo(Number + ': ' + Description);
}
function oWinsock_OnClose() {
oWinsock.CloseWinsock();
WScript.Echo(sSource);
oWinsock = null;
bClose = true;
}
while (!bClose) {
WScript.Sleep(1);
}
In the browser? Not really, but you can use WebSockets http://en.wikipedia.org/wiki/WebSocket
You'll need to implement a WebSocket server, so if you need to talk directly to a socket, you can't do it from a browser. But you could implement a proxy server that relays information between the socket server and the WebSocket server.
If you don't need two way communication, the best thing would be for your server to provide a webservice that wraps that socket request. Then your client can just make an AJAX call.