Develop Reference

Android and Java Ping/Pong Web Socket functionality

I have developed and Android application with is connecting to JAVA Web Socket and basically it is working very well.
The issue is, that sometimes the client is disconnected but connection at the server side is appearing to be connected.
I try to investigate, when and why it happened but unfortunately i could not find the a specific scenario that cause to this problem.
I have thought to implement Ping/Pong messaging between server and all clients and in case that there is no answer from the clients is to closed the connection at the server side.
i can easily implement such my private mechanism but I have read around and I understand that Java and Android has an build in Ping/Pong messaging mechanism but i was not able to find any example of that.
Can anyway, provide a simple example how to implement Ping/Pong messaging functionality using the build in tools?

I have succeed to implement Ping/Pong functionality between EE JAVA WebSocket and android application. The server is sending Ping message to client every 5 min. if server does not got Pong message back within 5 second, the server is closing client connection.
here is my solution if someone will need it:
WebSocket side:
public class User {
public ScheduledExecutorService pingExecutorService;
public Timer disconnectTimer;
private Session userSession;
private String userName;
public User(Session userSession) {
this.userSession = userSession;
}
public Session getUserSession() {
return userSession;
}
public void setUserSession(Session userSession) {
this.userSession = userSession;
}
public String getUserName() {
return userName;
}
public void setUserName(String userName) {
this.userName = userName;
}
}
#OnOpen
public void onOpen(Session session) {
User newUserConnection = new User(session);
connections.getConnections().put(session.getId(), newUserConnection);
schedulePingMessages(newUserConnection);
}
#OnClose
public void onClose(Session session) {
handleOnClose(session);
}
#OnMessage
public void onMessage(String message, Session session) {
messageHandler.handleMessage(message, session);
}
#OnMessage
public void onPong(PongMessage pongMessage, Session session) {
String sourceSessionId = session.getId();
User user = connections.getConnections().get(sourceSessionId);
user.disconnectTimer.cancel();
user.disconnectTimer.purge();
}
#OnError
public void onError(Throwable t) {
System.out.println(new Date() + "onError::" + t.getMessage());
t.printStackTrace();
}
private void schedulePingMessages(User newUserConnection) {
newUserConnection.pingExecutorService = Executors.newScheduledThreadPool(1);
newUserConnection.pingExecutorService.scheduleAtFixedRate(() -> {
scheduleDiconnection(newUserConnection);
try {
String data = "Ping";
ByteBuffer payload = ByteBuffer.wrap(data.getBytes());
newUserConnection.getUserSession().getBasicRemote().sendPing(payload);
} catch (IOException e) {
e.printStackTrace();
}
}, 300, 300, TimeUnit.SECONDS);
}
private void scheduleDiconnection(User user) {
user.disconnectTimer = new Timer();
user.disconnectTimer.schedule(new TimerTask() {
#Override
public void run() {
try {
user.getUserSession().close(new CloseReason(CloseCodes.UNEXPECTED_CONDITION," Client does not response"));
} catch (IOException e) {
// TODO Auto-generated catch block
e.printStackTrace();
}
}
}, 5000);
}
The android side just need to add the following override method:
#Override
public void onWebsocketPing(WebSocket conn, Framedata f) {
Log.i("ZCF","got Ping !");
super.onWebsocketPing(conn, f);
}

Can i connect an android client through native java.net.Socket with a node js server which uses socket.io?

I built a server using node.js and socket.io for a chat application and I want to connect to the server from my android client application that uses native java.net.Socket. Can I do it?

Here I found a solution that works fine. This code section is for server side socket.
var net = require('net');
var sockets = [];
var svr = net.createServer(function(sock) {
console.log('Connected: ' + sock.remoteAddress + ':' + sock.remotePort);
sockets.push(sock);
sock.write('Welcome to the server!\n');
sock.on('data', function(data) {
for (var i=0; i<sockets.length ; i++) {
if (sockets[i] != sock) {
if (sockets[i]) {
sockets[i].write(data);
}
}
}
});
sock.on('end', function() {
console.log('Disconnected: ' + sock.remoteAddress + ':' + sock.remotePort);
var idx = sockets.indexOf(sock);
if (idx != -1) {
delete sockets[idx];
}
});
});
var svraddr = '192.168.0.8';
var svrport = 1234;
svr.listen(svrport, svraddr);
console.log('Server Created at ' + svraddr + ':' + svrport + '\n');
Android client side code is given below: connect to the given ip and port for server through android client side.
import java.io.BufferedReader;
import java.io.IOException;
import java.io.InputStreamReader;
import java.io.OutputStream;
import java.net.InetSocketAddress;
import java.net.Socket;
public class Client {
private Socket socket;
private OutputStream socketOutput;
private BufferedReader socketInput;
private String ip;
private int port;
private ClientCallback listener=null;
public Client(String ip, int port){
this.ip=ip;
this.port=port;
}
public void connect(){
new Thread(new Runnable() {
#Override
public void run() {
socket = new Socket();
InetSocketAddress socketAddress = new InetSocketAddress(ip, port);
try {
socket.connect(socketAddress);
socketOutput = socket.getOutputStream();
socketInput = new BufferedReader(new InputStreamReader(socket.getInputStream()));
new ReceiveThread().start();
if(listener!=null)
listener.onConnect(socket);
} catch (IOException e) {
if(listener!=null)
listener.onConnectError(socket, e.getMessage());
}
}
}).start();
}
public void disconnect(){
try {
socket.close();
} catch (IOException e) {
if(listener!=null)
listener.onDisconnect(socket, e.getMessage());
}
}
public void send(String message){
try {
socketOutput.write(message.getBytes());
} catch (IOException e) {
if(listener!=null)
listener.onDisconnect(socket, e.getMessage());
}
}
private class ReceiveThread extends Thread implements Runnable{
public void run(){
String message;
try {
while((message = socketInput.readLine()) != null) { // each line must end with a \n to be received
if(listener!=null)
listener.onMessage(message);
}
} catch (IOException e) {
if(listener!=null)
listener.onDisconnect(socket, e.getMessage());
}
}
}
public void setClientCallback(ClientCallback listener){
this.listener=listener;
}
public void removeClientCallback(){
this.listener=null;
}
public interface ClientCallback {
void onMessage(String message);
void onConnect(Socket socket);
void onDisconnect(Socket socket, String message);
void onConnectError(Socket socket, String message);
}
}
MainActivity is:
public class MainActivity extends AppCompatActivity {
#Override
protected void onCreate(#Nullable Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
Client socket = new Client("192.168.0.8", 1234);
socket.setClientCallback(new Client.ClientCallback () {
#Override
public void onMessage(String message) {
}
#Override
public void onConnect(Socket socket) {
socket.send("Hello World!\n");
socket.disconnect();
}
#Override
public void onDisconnect(Socket socket, String message) {
}
#Override
public void onConnectError(Socket socket, String message) {
}
});
socket.connect();
}
}

The answer to your question is No. A java.net.socket cannot be connected with a nodejs socket.io because the protocol specifications are different for both.
Note: Socket.IO is not a WebSocket implementation. Although Socket.IO indeed uses WebSocket as a transport when possible, it adds some metadata to each packet: the packet type, the namespace and the ack id when a message acknowledgement is needed. That is why a WebSocket client will not be able to successfully connect to a Socket.IO server, and a Socket.IO client will not be able to connect to a WebSocket server (like ws://echo.websocket.org) either. Please see the protocol specification here.
Quoted From nodejs socket.io github page.So when web socket cannot be connected to socket.io so the java.net.socket can also be not connected.
If you want to have communication with the java client you can use the Socket.io library designed for java.

In Nodejs, You can use from this example
And in Sockect.io blog
In Java, as a server, you can use PrintWriter to write your data on Socket in a very simple situation. like below open socket on port 9090 and send current date to the client:
/**
* Runs the server.
*/
public static void main(String[] args) throws IOException {
ServerSocket listener = new ServerSocket(9090);
try {
while (true) {
Socket socket = listener.accept();
try {
PrintWriter out =
new PrintWriter(socket.getOutputStream(), true);
out.println(new Date().toString());
} finally {
socket.close();
}
}
}
finally {
listener.close();
}
}
Code from here

How to get Socket Id in Socket.io on Android?

I want to get the id of my socket running in Android. Everything is create normally and is able to send data back and forth but I need to get the Androids socket id for usage throughout the entire application. I have tried to find a solution but either they were outdated or does not work. Below is my latest attempt at solving this issue. With this attempt it errors saying that there are no elements in args[0]. I have also tried mSocket.id(); but that returns nothing.
public class GameSocket {
private Socket mSocket = null;
private static GameSocket mInstance;
public synchronized static GameSocket getInstance() {
if (mInstance == null) {
mInstance = new GameSocket();
}
return mInstance;
}
public void initialize() {
mSocket = IO.socket(URI.create(SERVER_URI));
mSocket.off();
mSocket.on(Socket.EVENT_CONNECT, new Emitter.Listener() {
#Override
public void call(Object... args) {
Log.d(GameSocket.class.getSimpleName(), "Event connection...");
mSocketId = args[0].toString();
Log.d("CONNECT ID", mSocketId);
}
})
.on(Socket.EVENT_ERROR, new Emitter.Listener() {
#Override
public void call(Object... args) {
if (args != null) {
Log.e(GameSocket.class.getSimpleName(), "Socket Event Error: " + args[0].toString());
}
}
});
}
}

Simple SignalR Android Example Issue

I am basically trying to send a message from my android to my server and the server to send back a response to my android app. I followed THIS tutorial.
Just a simple exercise to introduce myself in to SignalR using Azure Web API and Android.
My Complete Server code in C#:
public class TestHub: Hub {
public void SendMessage(string name, string message) {
// Call the broadcastMessage method to update clients.
Clients.All.broadcastMessage(name, message);
}
public void SendClientMessage(CustomType obj) {
Clients.All.broadcastMessage("From Server", "Server got the message bro");
}
public class CustomType {
public string Name;
public int Id;
}
}
Complete Android Java code:
public class MainActivity extends AppCompatActivity {
Handler handler;
TextView statustext;
#Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
handler = new Handler();
statustext = (TextView) findViewById(R.id.status);
Platform.loadPlatformComponent(new AndroidPlatformComponent());
// Change to the IP address and matching port of your SignalR server.
String host = "https://My-Service-name.azure-mobile.net/";
HubConnection connection = new HubConnection(host);
HubProxy hub = connection.createHubProxy("TestHub");
SignalRFuture < Void > awaitConnection = connection.start();
try {
awaitConnection.get();
} catch (InterruptedException e) {
} catch (ExecutionException e) {
}
hub.subscribe(this);
try {
hub.invoke("SendMessage", "Client", "Hello Server!").get();
hub.invoke("SendClientMessage",
new CustomType() {
{
Name = "Android Homie";
Id = 42;
}
}).get();
} catch (InterruptedException e) {
} catch (ExecutionException e) {
}
}
//I have no idea what the following method is for. Just followed the tutorial.. (blindly)
public void UpdateStatus(String status) {
final String fStatus = status;
handler.post(new Runnable() {
#Override
public void run() {
statustext.setText(fStatus);
}
});
}
public class CustomType {
public String Name;
public int Id;
}
}
Problems with this:
1. I get an exception:
java.util.concurrent.ExecutionException:
microsoft.aspnet.signalr.client.transport.NegotiationException: There
was a problem in the negotiation with the server
2. I feel like I haven't properly called the server from the Java code.
Should the URL be:
https://My-Service-name.azure-mobile.net/
or
https://My-Service-name.azure-mobile.net/api/signalr
Can someone clarify these doubts and help me set it up?

Servlet WebSocket Acessed by Android

I'm trying learn how to use the websocket and make a simple servlet for being connected with Android but I don't get it.
The index.jsp :
var ws = new WebSocket("ws://" + document.location.host + "/myws/ServletWS");
ws.onopen = function() { };
ws.onclose = function() { };
ws.onerror = function() { log("ERROR"); };
ws.onmessage = function(data) { var message = data.data; };
function sendMessage(msg) { ws.send(msg); }
How or where I receive the data from client?
Now on the servlet:
#Override protected StreamInbound createWebSocketInbound(String subProtocol, HttpServletRequest request) {
return new ConnectionWS();
}
class ConnectionWS extends MessageInbound {
private WsOutbound outbound;
#Override protected void onOpen(WsOutbound outbound) {
this.outbound = outbound;
}
#Override protected void onTextMessage(CharBuffer msg) throws IOException {
String message = msg.toString();
ServletWS.processData(message);
}
public void sendMessage(String message) {
CharBuffer cb = CharBuffer.wrap(message);
try {
outbound.writeTextMessage(cb);
} catch (IOException e) {}
}
}
public void processData(String message){
here I have to call the sendMessage with the answer to the client
}
I have saw a lot of examples on web but all of then about chat.
Thanks a lot for any help.

I understand that, you have a basic knowledge about tomcat configuration as well as java Servlet programming. As WekSocket is newly introduced in Tomcat, you may need to use latest tomcat version to implement WebSocket over it. I have used Apache Tomcat 7.0.42 for it.
So here we go. First, create a Servlet which will just create a new WebSocket for the request. You may need to modify it, if you want to go by session rather than request. Here is sample code.
import org.apache.catalina.websocket.StreamInbound;
import org.apache.catalina.websocket.WebSocketServlet;
public class WsChatServlet extends WebSocketServlet {
private static final long serialVersionUID = 1456546233L;
#Override
protected StreamInbound createWebSocketInbound(String protocol,
HttpServletRequest request) {
return new IncomingMessageHandler();
}
}
Now, create a Message Handler class which will handle each WebSocket stream independently. and that's it !
public class IncomingMessageHandler extends MessageInbound {
private WsOutbound myoutbound;
public IncomingMessageHandler() {
}
#Override
public void onOpen(WsOutbound outbound) {
logger.info("Open Client.");
this.myoutbound = outbound;
}
#Override
public void onClose(int status) {
logger.info("Close Client.");
}
/**
* Called when received plain Text Message
*/
#Override
public void onTextMessage(CharBuffer cb) throws IOException {
}
/**
* We can use this method to pass image binary data, eventually !
*/
#Override
public void onBinaryMessage(ByteBuffer bb) throws IOException {
}
public synchronized void sendTextMessage(String message) {
try {
CharBuffer buffer = CharBuffer.wrap(message);
this.getMyoutbound().writeTextMessage(buffer);
this.getMyoutbound().flush();
} catch (IOException e) {
}
}
/**
* Set websocket connection timeout in milliseconds,
* -1 means never
*/
#Override
public int getReadTimeout() {
return -1;
}
public WsOutbound getMyoutbound() {
return myoutbound;
}
public void setMyoutbound(WsOutbound myoutbound) {
this.myoutbound = myoutbound;
}
}

If not misunderstood and you want to use web sockets on Android then recommended API for you is jWebSocket.
Get it here, hopefully it already provides you APIs for a lot of the work that you need to do or even more.
http://jwebsocket.org/