Develop Reference

Clean up Redisson pub/sub listeners when assoicated object is 'stale'

I'm trying to implement a simple Websocket application in Java that is able to scale horizontally, by using Redis and the Redisson library.
The Websocket server basically keeps track of connected clients, and sends message that are received to an Rtopic - this works great.
To consume, I have code that adds a listener when a client is registered : it associated a Client object with a listener by:
private static RedissonClient redisson = RedissonRedisServer.createRedisConnectionWithConfig();
public static final RTopic subcriberTopic = redisson.getTopic("clientsMapTopic");
public static boolean sendToPubSub(ConnectedClient q, String message) {
boolean[] success = {true};
MessageListener<Message> listener = new MessageListener<Message>() {
#Override
public void onMessage(CharSequence channel, Message message) {
logger.debug("The message is : " + message.getMediaId());
try {
logger.debug("ConnectedClient mediaid: " + q.getMediaid() + ",Message mediaid " + message.getMediaId());
if (q.getMediaid().equals(message.getMediaId())) {
// we need to verify if the message goes to the right receiver
logger.debug("MESSAGE from PUBSUB to (" + q.getId() + ") # " + q.getSession().getId() + " " + message);
// this is the actual message to the websocket client
// this executes on the wrong connected client when the connection is closed and reopened
q.getSession().getBasicRemote().sendText(message.getMessage());
}
} catch (Exception e) {
e.printStackTrace();
success[0] = false;
}
}
};
int listenerId = subcriberTopic.addListener(Message.class, listener);
}
The problem I am observing is as follows:
initial connection from client registers listener associated with that object
sent message to the ws server gets picked up by listener and sent properly
disconnect websocket - create new connection - new listener gets created
sent message to the ws server gets picked up by same original listener and uses that connected client instead of the newly registered one
sending fails (because client and ws connection don't exist)and is not processes further
It seems I just need to remove the listener for the client if the client gets removed, but I haven't found a good way to do that because although I see in the debugger that the listener has the associated connected client object, I'm unable to retrieve them without adding code for that.
Am I observing this correctly and what is a good way to make this work properly?

When I was writing the question, I kind of leaned to an answer that I had in mind and tried, which worked.
I added a ConcurrentHashmap to keep track of the relation between the connected client and the listener.
In the logic where I handled websocket error that pointed to a client removing, I then removed the listener that was associated (and the entry from the map).
Now it works as expected.
small snippet:
int listenerId = subcriberTopic.addListener(Message.class, listener);
clientListeners.put(q,(Integer)listenerId);
And then in the websocket onError handler that triggers the cleanup:
// remove the associated listener
int listenerIdForClient = MessageContainer.clientListeners.get(cP);
MessageContainer.subcriberTopic.removeListener((Integer) listenerIdForClient);
// remove entry from map
MessageContainer.clientListeners.remove(cP);
Now the listener gets cleaned up properly and the next time a new listener gets created and handles the messages.

Canceling filewatcher run by TimerTask after receiving websocket message in Java

I've been coding around in circles trying to work this one out, new to java and have been lurking here to find things out for a while but I really can't get passed this one. I adapted some code by Desmond Shaw (http://www.codepool.biz/how-to-implement-a-java-websocket-server-for-image-transmission-with-jetty.html) to create a websocket to tranfer jpg images from a server to remote clients. I want to send files from the server to the browser windows of connected clients when some specific files on the server change (they are pages of music scores that are created using Max/MSP in real-time), but I don't seem to be able to cancel the timers I'm creating to watch these files in my home directory for changes.
More specifically I'm sending messages from the remote browser clients (through javascript buttons operated by the users) over a websocket connection to specify which of the files they wish to see updated on their screen (i.e part one, which refers to a file on the server called "1.png" and is the violin part, or part 2 which is the server file "2.png" and is the cello part etc). This is then used within the websocket handler running on my server to send the right files to that client when a filewatcher detects they have changed on the server. I can get everything going except stopping the timers running the filewatchers, when a different part is requested by the client (say the violin player wants to look at the cello players part). Below is the method I have edited to respond to the messages from the clients:
#OnWebSocketMessage //part request from websocket client (remote browser)
public void onMessage( String message) {
System.out.println("Message: '" + message + "' received");
sFclient = message;
if (sFclient == "1" || sFclient == "2" || sFclient == "3" || sFclient == "4") {
System.out.println("Part " + sFclient + " joined");
}
else {
sFclientOut = 0;
}
}
public void onChange( File file ) {
System.out.println( "File "+ file.getName() +" has changed!" );
TimerTask task = new FileWatcher(new File("/Users/benedict/" + message + ".png")) {
try {
File f = new File("/Users/benedict/" + sFclient + ".png");
BufferedImage bi = ImageIO.read(f);
ByteArrayOutputStream out = new ByteArrayOutputStream();
ImageIO.write(bi, "png", out);
ByteBuffer byteBuffer = ByteBuffer.wrap(out.toByteArray());
mSession.getRemote().sendBytes(byteBuffer);
out.close();
byteBuffer.clear();
}
catch (IOException e) {
e.printStackTrace();
}
Timer timer1 = new Timer(); {
timer1.schedule(task , new Date(), 20 );
if (sFclientOut == 0){
task.cancel();
timer1.cancel();
}
}
}
I had it working mostly using an if statement which I've now abandoned but have been editing and now it doesn't make as much sense probably. Any help at all would be appreciated, but my main question is should I be trying to cancel the threads handling the timertasks or use a completely different approach altogether like a switch statement for example. I have tried sending a message before every new message from the browsers ("0") to cancel the old threads but the Timertasks just don't start at all, which I think is because that cancels the timertask and doesn't let it run again?
Thanks,
Benedict

Ok here's the final working solution, I just had to cancel the tasks based on a message from the clients (in this case a 0)
else if (message.equals("0")) {
zerocounter = zerocounter + 1;
if (zerocounter >= 2) {
task.cancel();
}

Writing netty performance tests

So I have a netty-based websockets client that I am using for performance tests. My idea is that I can use it to simulate 100, 1000, etc simultaneous connections.
I've determined that my current approach to this is not working--the test harness is simply not creating enough websocket connections, althogh it bumps along happily, thinks it's still connected, etc. But my server simply does not show the correct number of connections when I use this test harness. I think most likely this is occurring because I am using various objects in the netty library across multiple threads at once and they don't handle that very well. ClientBootstrap, for example.
This is what I am doing per-thread. Can you tell me where I am going wrong, so that I can fix my test harness?
public void run(){
try{
// client bootstrap. There is one of these per thread. is that part of the problem?
ClientBootstrap bootstrap = new ClientBootstrap(new NIOClientSocketChannelFactory(Executors.newCachedThreadPool(), Executors.newCachedThreadPool())));
Channel ch = null;
try{
// set up ssl engine
final SSLEngine engine = createServerContext().createSSLEngine();
engine.setUseClientMode(true);
// there is a new handhsaker per thread, too. They all go to the same uri
final WebSocketClientHandshaker handshaker = new WebSocketClientHandhsakerFactory().newHandshaker(uri, WebSocketVersion.V08, null, false, null);
// set up the pipeline factory and pipeline
bootstrap.setPipelineFactory(new ChannelPipelieFactory(){
#Override
public Channelpipeline getPipeline() throws Exception(){
ChannelPipeline pipeline = Channels.pipeline();
pipeline.addLast("ssl", new SslHandler(engine));
pipeline.addLast("encoder", new HttpRequestEncoder();
pipeline.addLast("decoder", new HttpResponseDecoder();
// WebSocketClientHandler code not included, it's just a custom handler that sends requests via websockets
pipeline.addLast("ws-handler", new WebSocketClientHandler(handshaker);
return pipleline;
}
});
// connect websockets preflight over http
ChannelFuture future = bootstrap.connect(new InetSocketAddress(uri.getHost(), uri.getPort());
future.sync();
// do websockets handshake
ch = future.getChannel();
ChannelFuture handshakeFuture = handshaker.handshake(ch);
handshakeFuture.syncUninterruptably();
Thread.sleep(1000); // i had to add this. Sync should have meant that the above method didn't return until it was complete... but that was a lie. So I sleep for 1 second to solve that problem.
if(!handshakeDuture.isSuccess())
System.out.println("WHOAH errror");
// send message to server
ch.write(new TextWebSocketFrame("Foo"));
// wait for notifications to close
while(!getShutdownNow().get()) // shutdownNow is an atomicBoolean which is set to true when all my threads have been started up and a certain amount of time has passed
Thread.sleep(2000);
// send close; wait for response
ch.write(new CloseWebSocketFrame());
ch.getCloseFuture().awaitUninterruptibly();
}
}
}
}

java websphere MQ

My aim is to put n number of messages in a for loop to a WebSphere MQ queue using WebSphere MQ java programming.
My java program will run as a standalone program.
If any exception in between , I need to rollback all the messages.
If no exception then I should commit all the messages .
The outside world should not see my messages in the queue until I complete fully.
How do I achieve this?
Updated with sample code as per reply from T.Rob:
Please check if sample code is fine ?
Does setting MQGMO_SYNCPOINT is only related to my program's invocation ?
(because similar programs running parallely will also be putting messages on the same queue and those messages should not gett affected by my program's SYNCPOINT.)
public void sendMsg() {
MQQueue queue = null;
MQQueueManager queueManager = null;
MQMessage mqMessage = null;
MQPutMessageOptions pmo = null;
System.out.println("Entering..");
try {
MQEnvironment.hostname = "x.x.x.x";
MQEnvironment.channel = "xxx.SVRCONN";
MQEnvironment.port = 9999;
queueManager = new MQQueueManager("XXXQMANAGER");
int openOptions = MQConstants.MQOO_OUTPUT;
queue = queueManager.accessQueue("XXX_QUEUENAME", openOptions, null, null, null);
pmo = new MQPutMessageOptions();
pmo.options = CMQC.MQGMO_SYNCPOINT;
String input = "testing";
System.out.println("sending messages....");
for (int i = 0; i < 10; i++) {
input = input + ": " + i;
mqMessage = new MQMessage();
mqMessage.writeString(input);
System.out.println("Putting message: " + i);
queue.put(mqMessage, pmo);
}
queueManager.commit();
System.out.println("Exiting..");
} catch (Exception e) {
e.printStackTrace();
try {
System.out.println("rolling back messages");
if (queueManager != null)
queueManager.backout();
} catch (MQException e1) {
e1.printStackTrace();
}
} finally {
try {
if (queue != null)
queue.close();
if (queueManager != null)
queueManager.close();
} catch (MQException e) {
e.printStackTrace();
}
}
}

WMQ supports both local and global (XA) units of work. The local units of work are available simply by specifying the option. Global XA transactions require a transaction manager, as mentioned by keithkreissl in another answer.
For what you described, a POJO doing messaging under syncpoint, specify MQC.MQGMO_SYNCPOINT in your MQGetMessageOptions. When you are ready to commit, issue the MQQManager.commit() or MQQManager.backout() call.
Note that the response and doc provided by ggrandes refers to the JMS and not Java classes. The Java classes use Java equivalents of the WMQ procedural API, can support many threads (doc) and even provide connection pooling (doc). Please refer to the Java documentation rather than the JMS documentation for the correct behavior. Also, I've linked to the WMQ V7.5 documentation which goes with the latest WMQ Java V7.5 client. The later clients have a lot more local functionality (tracing, flexible install path, MQClient.ini, etc.) and work with back-level QMgrs. It is highly recommended to be using the latest client and the download is free.

you only need to create a session with transaction enabled.
Session session;
// ...
boolean transacted = true;
session = connection.createSession(transacted, Session.AUTO_ACKNOWLEDGE);
try {
// ...do things...
session.commit();
} catch (Exception e) {
session.rollback();
}
// ...
WARN-NOTE: Sessions are not thread-safe ;-)
Doc Websphere MQ/JMS

If you have access to a transaction manager and more importantly an XATransaction wired up to your MQ access, you can start a transaction at the beginning of your message processing put all the messages on the queue then commit the transaction. Using the XATransactions it will not put any messages until the transaction commits. If you don't have access to that, you can do a little more plumbing by placing your messages in a local data object, wrap your code in a try/catch if no exceptions iterate through the local data object sending the messages. The issue with the later approach is that it will commit all your other processing but if a problem occurs in the sending of messages your other processing will not be rolled back.

Function hangs? on packet.setAddress()

Ok so the program is designed to take in connections, validate them, and resend that validation code. Before anyone get's angry it's just a simple little project and is not designed to be overly complex haha. However for some very strange reason the function is hanging on send.setAddess(packet.getAddress); I know this because I have commented out each individual line of code that deals with the Datagram packet "send" and have found that it "hangs" (or never progresses forward in the method again) on that particular line. Any thoughts? Am I doing something cluelessly wrong? I tried it on a linux server as well to make sure it didn't have anything to do with me and the same crap happened.
public static boolean authorize(String n, DatagramPacket packet) {
DatagramPacket send = new DatagramPacket(new byte[4096], 4096);
try {
System.out.println("in auth");
String[] t1 = n.split("%#");
String name = t1[1];
int k = genKey(name);
clients.put(name, k);
send.setAddress(packet.getAddress());
System.out.println("set add");
send.setPort(packet.getPort());
System.out.println("set port");
send.setData(("l-succeed%#" + Integer.toString(k)).getBytes());
System.out.println("set data");
main.dispathcer(send);
System.out.println("called send");
return true;
} catch(Exception e) {
send.setData("l-failed".getBytes());
main.dispathcer(send);
return false;
}
}
EDIT: it took 6 minutes before the authorization token was received by the client. So obviously the setAddress() works but is taking far too long...

It's possible that the process is hanging because there's an issue doing DNS resolution on the address for packet when you call .getAddress(). A few DNS calls are made in order to create the InetAddress object. On these machines, are you able to do a reverse DNS lookup on the IP that the packet packet came from? Try setting an entry for this IP in your /etc/hosts file.