Myujth

I have written the PAHO-client MQTT programs in Java and using mosquitto-broker.

Publisher snippet code: Publisher sending the numbers from 0 to 254.

char charset = new char[255]; 
for(int i=0;i< 255;i++)

 charset[i] = (char)i;
 System.out.println(i+" "+(int)charset[i]);


String str2 = String.valueOf(charset);
MqttMessage message1 = new MqttMessage();
message1.setPayload(str2.getBytes()); 
client.publish("temperature",message1);

Subscriber snippet code: Subscriber is expected to recieve numbers from 0 to 254.

byte ascii = message.getBytes(); 
for (int i = 0; i <ascii.length; i++) 
 
 System.out.println(i +" "+(long)(ascii[i] & 0xFF)); 

Output Snapshots:
Publisher output

subscriber ouput

Problem in subscriber output:

The index from 128 to 159 in subscriber output is receiving the value '63' instead of the
normal numbers which are being sent from publisher side.

Why not using byte arrays

Publisher

byte payload = new byte[255]; 
for(int i = 0; i < 255;i ++) 
 payload[i] = (byte)i;


message.setPayload(payload); 
client.publish("temperature", message);

Subscriber

byte paylaod = message.getPayload();
for (int i = 0; i < payload.length; i++) 
 System.out.println(i +" "+(int)(payload[i] & 0xFF)); 

But the problem is mostly related how Java encodes String a char is a 16-bit UTF-16 encoded character. A String is a "char array with additional features".

So if you call String#getBytes() the UTF-16 data gets converted to UTF-8, which causes in your case data loose. String are not designed to carry binary Data