Re: [paho-dev] mqtt publisher topic

[Dave Locke <locke@xxxxxxxxxx>]

When sending messages between a producing
application (publisher) and consuming application (subscriber) they both
need to use the same name space in order to  exchange messages.  With
pub sub the name space is via topic hierarchy.   For instance if an
application is going to produce messages about stock price it might use
a topic space of stock/<stocksymbol>  with real instances of
 stock/IBM,  stock/MS, stock/google        
 The consuming application needs to be informed of the name space
and can then subscribe to a specific stock such as stock/google or for
all stock prices  using a wildcard subscription like stock/#

Based on this, If you are need an application
to publish messages that you consume,

• Ensure the publisher knows the topic that you are subscribed to
• Subscribe to a top level topic + wild card and ensure the publisher uses the top level topic + one or more subtopics.
• To see all messages going through a broker then subscribe to # and all (authorised) messages going through the mqtt broker will be seen by the subscriber
  

One of the principals of messaging
is to decouple the producer from the consumer typically via an intermediate
broker and a name space like a topic or a queue.  As a result of the
decoupling, knowledge of the producer such as its IP address is not made
available to the consumer.  If there is a need to do so then details
of the producer could be flowed in the payload of the message.  

All the best 
Dave

  



From:      
 kanna dhasan <thasanmca@xxxxxxxxx>
To:      
 paho-dev@xxxxxxxxxxx,

Date:      
 13/08/2012 06:17
Subject:    
   [paho-dev] mqtt
publisher topic
Sent by:    
   paho-dev-bounces@xxxxxxxxxxx

---

Dear sir 



               I already have  a
broker running on my server and have subscribed few topics. If a new client
wants to send his data to my server through my mqtt broker. Is there a
possibility to obtain his ip address , publisher id ( and his new topic
which he s gonna publish). Right now i am sending a sample program in which
, if the publisher sends his data through the already subscribed topic
then messages are received. If a new client connect to my broker with a
new unsubscribed topic . how can i identify the topic name and publisher
id, ip address. The subscriber program is as follows 

package Testing;
import java.sql.Connection;
import java.sql.DriverManager;
import java.sql.PreparedStatement;
import java.sql.ResultSet;
import java.util.ArrayList;
import java.util.Iterator;
import java.util.List;
import java.io.IOException;
import java.io.InputStreamReader;
import org.eclipse.paho.client.mqttv3.MqttCallback;
import org.eclipse.paho.client.mqttv3.MqttClient;
import org.eclipse.paho.client.mqttv3.MqttDeliveryToken;
import org.eclipse.paho.client.mqttv3.MqttException;
import org.eclipse.paho.client.mqttv3.MqttMessage;
import org.eclipse.paho.client.mqttv3.MqttTopic;
import org.eclipse.paho.client.mqttv3.internal.TCPNetworkModule;

public class subs implements MqttCallback 
{

private static final String SERVER_URL = "tcp://localhost:1883";
private static final String CLIENT_ID = "myclient";

public String topic="com/newregistration";

private static MqttClient mqttClient;



public static void main(String[] args)throws Exception
{
subs obj=new subs();
obj.test();
}


public void test() throws Exception {
try {


mqttClient = new MqttClient(SERVER_URL, CLIENT_ID);
mqttClient.connect();

mqttClient.setCallback((MqttCallback) this);

System.out.println("connected with broker");
//mqttTopic.publish(message);


mqttClient.subscribe(topic); 
}
catch (MqttException e) {
e.printStackTrace();
}
}

     
public void connectionLost(Throwable cause) {
System.out.println("Connection Exist. \nCause: " + cause);
}


public void messageArrived(MqttTopic topic, MqttMessage message)
throws Exception {
System.out.println("Message arrived From The Topic:\t"+topic.toString()
+" \nMessage: " + message.toString());
}


public void deliveryComplete(MqttDeliveryToken token) {
System.out.println("Delivery complete. \nToken: " + token.toString());
}


}

The publisher program is as follows 


package Testing;
import java.io.BufferedReader;
import java.io.IOException;
import java.io.InputStreamReader;
import java.util.Calendar;
import java.util.Date;


import org.eclipse.paho.client.mqttv3.MqttClient;
import org.eclipse.paho.client.mqttv3.MqttDeliveryToken;
import org.eclipse.paho.client.mqttv3.MqttException;
import org.eclipse.paho.client.mqttv3.MqttMessage;
import org.eclipse.paho.client.mqttv3.MqttTopic;

public class ClientPublisher {

private static final String SERVER_URI = "tcp://localhost:1883";
private static final String 
CLIENT_ID = "pub";
private MqttClient mqttClient;
public static String topic="hello";

public static void main(String args[]) throws Exception
{
new ClientPublisher().doMqttTest(topic);
}


public void doMqttTest(String clienttopic) throws IOException
{
try {
mqttClient = new MqttClient(SERVER_URI, CLIENT_ID);
mqttClient.connect();
} catch (MqttException e) {
e.printStackTrace();
}

while (true) {
//Date date = Calendar.getInstance().getTime();
String date="hey";
//System.out.println(date.toString());
try {
// Get an instance of the topic
MqttTopic topic = mqttClient.getTopic(clienttopic);
MqttMessage message = new MqttMessage(date.toString().getBytes());
MqttDeliveryToken token = topic.publish(message);
//System.out.println(topi);
// Wait until the message has been delivered to the server
token.waitForCompletion();
Thread.sleep(50 * 1000);
break;
} catch (Exception e) {
e.printStackTrace();
}
}
}
}


Regards 
Kannadhasan
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