Develop Reference

FileWriter closes websocket connection?

I am new to server programming and websockets and I've learnt a little bit of Java 8 this year. In school we had a project where a client webpage opens your webcam, takes a photo of a barcode and then shows a photo and the nutritional value of said product. You can also just send a raw barcode number and that is what is done in this example
My side of the project was to implement a java websocket server (the backend) using the glassfish tyrus library, then receiving the number of the barcode in string format and making a request to openfoodfacts.org using their api. Finally I parsed the json file and sent it back as string format so the client app can read the string and show the correct information (product name, image url, etc)
My code is organized into two files, Serveur.java establishes a websocket server for the client to connect to and ProduitApi.java gets the information from openfoodfacts.org with the given barcode from the client.
public class Serveur {
#javax.websocket.server.ServerEndpoint(value = "/websocket")
public static class EndPoint {
#javax.websocket.OnClose
public void onClose(javax.websocket.Session session, javax.websocket.CloseReason close_reason) {
System.out.println("onClose: " + close_reason.getReasonPhrase());
}
#javax.websocket.OnError
public void onError(javax.websocket.Session session, Throwable throwable) {
System.out.println("onError: " + throwable.getMessage());
}
#javax.websocket.OnMessage
public void onMessage(javax.websocket.Session session, String message) {
System.out.println("Message from client: " + message);
//Creation du produit avec le message du client
try {
ProduitApi produit = new ProduitApi(message);
session.getBasicRemote().sendText(produit.print());
} catch (Exception e) {
e.printStackTrace();
}
}
#javax.websocket.OnOpen
public void onOpen(javax.websocket.Session session, javax.websocket.EndpointConfig ec) throws java.io.IOException {
System.out.println("OnOpen... " + ec.getUserProperties().get("Author"));
session.getBasicRemote().sendText("{\"Handshaking\": \"Yes\"}");
}
}
public static void main(String[] args) {
Server server;
server = new Server ("localhost", 8025, "/BetterFood", null, EndPoint.class);
try {
server.start();
System.out.println("--- server is running");
System.out.println(java.nio.file.FileSystems.getDefault().getPath("client") );
System.out.print("Please press a key to stop the server.");
java.io.BufferedReader reader = new java.io.BufferedReader(new java.io.InputStreamReader(System.in));
reader.readLine();
} catch (Exception e) {
e.printStackTrace();
} finally {
server.stop();
}
}
}
as you can see, when I receive the 'barcode' message, onMessage() gets called. There I instantiate an object of class ProduitApi to use the barcode to then return the information
This is my ProduitApi file without some unnecessary details
package com.gabi.serveur;
/**
*
* #author gabriel
*/
[imports]
public class ProduitApi {
private java.lang.String barcode;
final private java.net.URL url;
private java.net.URLConnection connection;
JsonObjectBuilder constructeur_objet = Json.createObjectBuilder();
String string_json;
ProduitApi(java.lang.String barcode)throws MalformedURLException, IOException {
this.barcode = barcode;
this.url = new java.net.URL("http://world.openfoodfacts.org/api/v0/product/" + this.barcode + ".json");
connection = url.openConnection();
stream();
}
public void stream() throws IOException{
if (connection != null) {
java.io.InputStreamReader response = new java.io.InputStreamReader(connection.getInputStream());
javax.json.stream.JsonParser parser=javax.json.Json.createParser(response);
while (parser.hasNext()) {
[parsing inputStream into JsonObject]
}
public String print()throws IOException{
string_json = constructeur_objet.build().toString();
System.out.print(string_json);
//FileWriter file = new FileWriter("serveur/src/main/java/com/gabi/serveur/json/final.json");
//file.write(string_json);
//file.close();
return string_json;
}
}
My problem comes from the last function ProduitApi.print() , it is supposed to return the parsed json in string form so I can send it via the sendText() as well as printing the result into my console so I can see if everything went right. As you can see there are somme commented lines; The FileWriter object that I had created was used with the purpose of writing said string to a file in my pc and let me check inside.
HOWEVER
and here is what I don't understand, If I uncomment those lines so that the print function can also write the file to my drive, The Connection Closes and then Opens again
It can be seen in the console where after printing the json string, it prints OnClose, followed by OnOpen Signaling the connection was reset for some reason.
If I remove the FileWriter section, the connection works normally, the client's connection stays open and he can make another request
End of Console Message after request:
...cuits x22 biscuits fourrés - 304g","qte":"304 g","img":"https://images.openfoodfacts.org/images/products/800/050/031/0427/front_fr.177.400.jpg"}onClose: OnOpen... null...
Finally, my question is just why writing to a file makes my program behave this way (resetting the connection). Does it have anything to do with how streams work?
I accidentally commented the filewriter portion when another Ide said it didn't find the file because I had opened the project from a different directory.

Prevent automatic exit on unsuccessful ActiveMQ reconnect

I have a small spring-boot app set up that connects to one or more Topics on ActiveMQ, which are set in the application's application.properties file on startup - and then sends these messages on to a database.
This is all working fine, but I am having some problems when trying to implement a failover - basically, the app will try to reconnect, but after a certain number of retries, the application process will just automatically exit, preventing the retry (ideally, I would like the app to just retry forever until killed manually or ActiveMQ becomes available again). I have tried explicitly setting the connection options (such as maxReconnectAttempts) in the connection URL (using url.options in application.properties) to -1/0/99999 but none of these seem to be right as the behavior is the same each time. From looking at the advice on Apache's own reference page I would also expect this behavior to be working as default too.
If anyone has any advice to force the app not to quit, I would be very grateful! The bits of my code that I think will matter is below:
#Configuration
public class AmqConfig {
private static final Logger LOG = LogManager.getLogger(AmqConfig.class);
private static final String LOG_PREFIX = "[AmqConfig] ";
private String clientId;
private static ArrayList<String> amqUrls = new ArrayList<>();
private static String amqConnectionUrl;
private static Integer numSubs;
private static ArrayList<String> destinations = new ArrayList<>();
#Autowired
DatabaseService databaseService;
public AmqConfig (#Value("${amq.urls}") String[] amqUrl,
#Value("${amq.options}") String amqOptions,
#Value("${tocCodes}") String[] tocCodes,
#Value("${amq.numSubscribers}") Integer numSubs,
#Value("${clientId}") String clientId) throws UnknownHostException {
Arrays.asList(amqUrl).forEach(url -> {
amqUrls.add("tcp://" + url);
});
String amqServerAddress = "failover:(" + String.join(",", amqUrls) + ")";
String options = Strings.isNullOrEmpty(amqOptions) ? "" : "?" + amqOptions;
this.amqConnectionUrl = amqServerAddress + options;
this.numSubs = Optional.ofNullable(numSubs).orElse(4);
this.clientId = Strings.isNullOrEmpty(clientId) ? InetAddress.getLocalHost().getHostName() : clientId;
String topic = "Consumer." + this.clientId + ".VirtualTopic.Feed";
if (tocCodes.length > 0){
Arrays.asList(tocCodes).forEach(s -> destinations.add(topic + "_" + s));
} else { // no TOC codes = connecting to default feed
destinations.add(topic);
}
}
#Bean
public ActiveMQConnectionFactory connectionFactory() throws JMSException {
LOG.info("{}Connecting to AMQ at {}", LOG_PREFIX, amqConnectionUrl);
LOG.info("{}Using client id {}", LOG_PREFIX, clientId);
ActiveMQConnectionFactory connectionFactory =
new ActiveMQConnectionFactory(amqConnectionUrl);
Connection conn = connectionFactory.createConnection();
conn.setClientID(clientId);
conn.setExceptionListener(new AmqExceptionListener());
conn.start();
destinations.forEach(destinationName -> {
try {
for (int i = 0; i < numSubs; i++) {
Session session = conn.createSession(false, Session.AUTO_ACKNOWLEDGE);
Destination destination = session.createQueue(destinationName);
MessageConsumer messageConsumer = session.createConsumer(destination);
messageConsumer.setMessageListener(new MessageReceiver(databaseService, destinationName));
}
} catch (JMSException e) {
LOG.error("{}Error setting up queue # {}", LOG_PREFIX, destinationName);
LOG.error(e.getMessage());
}
});
return connectionFactory;
}
}
public class MessageReceiver implements MessageListener, ExceptionListener {
public static final Logger LOG = LogManager.getLogger(MessageReceiver.class);
private static final String LOG_PREFIX = "[Message Receiver] ";
private DatabaseService databaseService;
public MessageReceiver(DatabaseService databaseService, String destinationName){
this.databaseService = databaseService;
LOG.info("{}Creating MessageReceiver for queue with destination: {}", LOG_PREFIX, destinationName);
}
#Override
public void onMessage(Message message) {
String messageText = null;
if (message instanceof TextMessage) {
TextMessage tm = (TextMessage) message;
try {
messageText = tm.getText();
} catch (JMSException e) {
LOG.error("{} Error getting message from AMQ", e);
}
} else if (message instanceof ActiveMQMessage) {
messageText = message.toString();
} else {
LOG.warn("{}Unrecognised message type, cannot process", LOG_PREFIX);
LOG.warn(message.toString());
}
try {
databaseService.sendMessageNoResponse(messageText);
} catch (Exception e) {
LOG.error("{}Unable to acknowledge message from AMQ. Message: {}", LOG_PREFIX, messageText, e);
}
}
}
public class AmqExceptionListener implements ExceptionListener {
public static final Logger LOG = LogManager.getLogger(AmqExceptionListener.class);
private static final String LOG_PREFIX = "[AmqExceptionListener ] ";
#Override
public void onException(JMSException e){
LOG.error("{}Exception thrown by ActiveMQ", LOG_PREFIX, e);
}
}
The console output I get from my application is just the below (apologies, as it is not much to go off)
[2019-12-12 14:43:30.292] [WARN ] Transport (tcp://[address]:61616) failed , attempting to automatically reconnect: java.io.EOFException
[2019-12-12 14:43:51.098] [WARN ] Failed to connect to [tcp://[address]:61616] after: 10 attempt(s) continuing to retry.
Process finished with exit code 0

Very interesting Question!
Configuring the maxReconnectAttempts=-1 will cause the connection attempts to be retried forever, but what I feel the problem here are as follows:
You are trying to connect to ActiveMQ while creating the Bean at App
startup, If ActiveMQ is not running when APP is starting up, the
Bean creation would retry the connection attempts forever causing a
timeout and not letting the APP to start.
Also when the ActiveMQ stops running midway you are not reattempting the connection as it is done inside #Bean and will only happen on APP startup
Hence the Connection shouldn't happen at Bean creation time, but maybe it can be done after the APP is up (maybe inside a #PostConstruct block)
These are just the pointers, You need to take it forward
Hope this helps!
Good luck!

How to access the payload of the message arrived of the callback method (messageArrived) in the main method Eclipse Paho?

Problem statement:- I am trying to automate a MQTT flow, for that I a need to publish and subscribe to multiple topics but in a sequential order. The trick part is that the message received from the first publish has some value which will be passed in the next sub/pub commands.
For eg.
Sub to topicA/abc
Pub to topicA/abc
Message received on topicA/abc is xyz
sub to topic topicA/xyz
pub to topic topicA/xyz
I am able to receive the message on the first topic but I am not getting how to access the payload of the received message in the main method and pass and attach it to the next topic for next sub.
Is there a way to get the retrieved the message payload from messageArrived callback method to the main method where is client instance is created?
Note:- I am using a single client for publish and subscribe.
kindly help me out as I have ran out of options and methods to do so.
Edited:-
Code snippet
Main class
public class MqttOverSSL {
String deviceId;
MqttClient client = null;
public MqttOverSSL() {
}
public MqttOverSSL(String deviceId) throws MqttException, InterruptedException {
this.deviceId = deviceId;
MqttConnection mqttConObj = new MqttConnection();
this.client = mqttConObj.mqttConnection();
}
public void getLinkCodeMethod() throws MqttException, InterruptedException {
client.subscribe("abc/multi/" + deviceId + "/linkcode", 0);
publish(client, "abc/multi/" + deviceId + "/getlinkcode", 0, "".getBytes());
}
}
Mqtt Claback impl:-
public class SimpleMqttCallBack implements MqttCallback {
String arrivedMessage;
#Override
public void connectionLost(Throwable throwable) {
System.out.println("Connection to MQTT broker lost!");
}
#Override
public void messageArrived(String s, MqttMessage mqttMessage) throws Exception {
arrivedMessage = mqttMessage.toString();
System.out.println("Message received:\t" + arrivedMessage);
linkCode(arrivedMessage);
}
#Override
public void deliveryComplete(IMqttDeliveryToken iMqttDeliveryToken) {
System.out.println("Delivery complete callback: Publish Completed "+ Arrays.toString(iMqttDeliveryToken.getTopics()));
}
public void linkCode(String arrivedMessage) throws MqttException {
System.out.println("String is "+ arrivedMessage);
Gson g = new Gson();
GetCode code = g.fromJson(arrivedMessage, GetCode.class);
System.out.println(code.getLinkCode());
}
}
Publisher class:-
public class Publisher {
public static void publish(MqttClient client, String topicName, int qos, byte[] payload) throws MqttException {
String time = new Timestamp(System.currentTimeMillis()).toString();
log("Publishing at: "+time+ " to topic \""+topicName+"\" qos "+qos);
// Create and configure a message
MqttMessage message = new MqttMessage(payload);
message.setQos(qos);
// Send the message to the server, control is not returned until
// it has been delivered to the server meeting the specified
// quality of service.
client.publish(topicName, message);
}
static private void log(String message) {
boolean quietMode = false;
if (!quietMode) {
System.out.println(message);
}
}
}

OK, it's a little clearer what you are trying to do now.
Short answer No, you can not pass values back to the "main method". MQTT is asynchronous that means you have no idea when a message will arrive for a topic you subscribe to.
You need to update your code to deal check what the incoming message topic is and then deal do what ever action you wanted to do with that response in the messageArrived() handler. If you have a sequence of task to do then you may need to implement what is known as a state machine in order to keep track of where you are in the sequence.

pIRCbot won't join Twitch channel or send messages

The following code connects to Twitch's IRC successfully and triggers the onConnect method which is where everything stops.
Because pIRCbot has verbose enabled I can see that it does send JOIN #twitchplayspokemon after connecting but the specification says that I should get an immediate response with the same text followed by a list of users (which would trigger the onJoin and onUserList methods) which doesn't happen.
I have also tried connecting to my channel and sending a message with
joinChannel("#[mychannelname]");
sendMessage("#[mychannelname]", "Hello World");
All this does is send two JOIN commands and doesn't ever join nor message appear in chat.
The tutorial/reference I'm using is http://help.twitch.tv/customer/portal/articles/1302780-twitch-irc
Other responses are also not being output. I am getting the MOTD but not seeing the "End of /MOTD command".
import org.jibble.pircbot.*;
public class MyBotMain extends PircBot {
public static void main(String[] args) throws Exception {
MyBotMain bot = new MyBotMain();
bot.setVerbose(true);
bot.setName("[myname]");
bot.setLogin("[myname]");
try {
bot.connect("irc.twitch.tv", 6667, "oauth:db4aai4mh474ikbgzzuh76fv67n"); // Not the key I'm using
} catch (NickAlreadyInUseException e) {
System.err.println("Nickname is currently in use");
} catch (IrcException e) {
System.err.println("Server did not accept connection");
e.printStackTrace();
}
}
#Override
protected void onConnect() {
System.out.println("Connected!");
joinChannel("#witchplayspokemon");
super.onConnect();
}
#Override
protected void onJoin(String channel, String sender, String login, String hostname) {
System.out.println(login + " joined channel " + channel);
super.onJoin(channel, sender, login, hostname);
}
#Override
protected void onUserList(String channel, User[] users) {
for (User user : users) {
System.out.println(user);
}
super.onUserList(channel, users);
}
}

Your code works perfectly fine, the only problem is that the channel you are trying to join is "witchplayspokemon" instead of "twitchplayspokemon" the onUserList(String channel, User[] users) is only giving me one user, But I have been having that problem recently on my own Bot So I am not yet sure on the cause.

Pusher: Decrease timeout for connection state

I'm currently experimenting with websockets using the Pusher library for Java.
Pusher automatically changes its connection state from CONNECTED to DISCONNECTED if the internet connection is lost. However, this only seems to happen after 150 seconds of being disconnected. This is very unfortunate as in those 150s, a lot of messages can get lost, and a de facto old message can still be seen as the most up-to-date.
How can I know if the last received message is the most up-to-date? Or is there any way to decrease the timeout for the connection state?
Here is the pusher code I'm using:
import com.pusher.client.Pusher;
import com.pusher.client.channel.Channel;
import com.pusher.client.channel.ChannelEventListener;
import com.pusher.client.channel.SubscriptionEventListener;
import com.pusher.client.connection.ConnectionEventListener;
import com.pusher.client.connection.ConnectionState;
import com.pusher.client.connection.ConnectionStateChange;
public class Testing {
public static void main(String[] args) throws Exception {
// Create a new Pusher instance
Pusher pusher = new Pusher("PusherKey");
pusher.connect(new ConnectionEventListener() {
#Override
public void onConnectionStateChange(ConnectionStateChange change) {
System.out.println("State changed to " + change.getCurrentState() +
" from " + change.getPreviousState());
}
#Override
public void onError(String message, String code, Exception e) {
System.out.println("There was a problem connecting!");
}
}, ConnectionState.ALL);
// Subscribe to a channel
Channel channel = pusher.subscribe("channel", new ChannelEventListener() {
#Override
public void onSubscriptionSucceeded(String channelName) {
System.out.println("Subscribed!");
}
#Override
public void onEvent(String channelName, String eventName, String data) {
System.out.println("desilo se");
}
});
// Bind to listen for events called "my-event" sent to "my-channel"
channel.bind("my-event", new SubscriptionEventListener() {
#Override
public void onEvent(String channel, String event, String data) {
System.out.println("Received event with data: " + data);
}
});
while(true){
try {
Thread.sleep(1000);
} catch(InterruptedException ex) {
Thread.currentThread().interrupt();
}
}
}
}
}

Just found the answer: Initiate Pusher-object with PusherOptions-object.
Here is the PusherOptions-class: http://pusher.github.io/pusher-java-client/src-html/com/pusher/client/PusherOptions.html
Here is a simple example how I decreased my connection-timeout from 150s to 15s:
// Define timeout parameters
PusherOptions opt = new PusherOptions();
opt.setActivityTimeout((long)10000L);
opt.setPongTimeout((long)5000L);
// Create a new Pusher instance
Pusher pusher = new Pusher(PUSHER_KEY, opt);
ActivityTimeout defines how often a ping is sent out to check the connectivity, PongTimeout defines the waiting time until a response from the ping-signal is expected.
The minimum ActivityTimeout is 1000ms, however such a low value is strongly discouraged by Pusher, probably to decrease the server-traffic.