org.eclipse.paho.client.mqttv3

Interface MqttCallback

All Known Subinterfaces:

MqttCallbackExtended

public interface MqttCallback

Enables an application to be notified when asynchronous events related to the client occur. Classes implementing this interface can be registered on both types of client: IMqttClient.setCallback(MqttCallback) and IMqttAsyncClient.setCallback(MqttCallback)

Method Summary

Modifier and Type	Method and Description
void	connectionLost(java.lang.Throwable cause) This method is called when the connection to the server is lost.
void	deliveryComplete(IMqttDeliveryToken token) Called when delivery for a message has been completed, and all acknowledgments have been received.
void	messageArrived(java.lang.String topic, MqttMessage message) This method is called when a message arrives from the server.

Method Detail

connectionLost

void connectionLost(java.lang.Throwable cause)

This method is called when the connection to the server is lost.

Parameters:

cause - the reason behind the loss of connection.

messageArrived

void messageArrived(java.lang.String topic,
                    MqttMessage message)
             throws java.lang.Exception

This method is called when a message arrives from the server.

This method is invoked synchronously by the MQTT client. An acknowledgment is not sent back to the server until this method returns cleanly.

If an implementation of this method throws an Exception, then the client will be shut down. When the client is next re-connected, any QoS 1 or 2 messages will be redelivered by the server.

Any additional messages which arrive while an implementation of this method is running, will build up in memory, and will then back up on the network.

If an application needs to persist data, then it should ensure the data is persisted prior to returning from this method, as after returning from this method, the message is considered to have been delivered, and will not be reproducible.

It is possible to send a new message within an implementation of this callback (for example, a response to this message), but the implementation must not disconnect the client, as it will be impossible to send an acknowledgment for the message being processed, and a deadlock will occur.

Parameters:

topic - name of the topic on the message was published to

message - the actual message.

Throws:

java.lang.Exception - if a terminal error has occurred, and the client should be shut down.

deliveryComplete

void deliveryComplete(IMqttDeliveryToken token)

Called when delivery for a message has been completed, and all acknowledgments have been received. For QoS 0 messages it is called once the message has been handed to the network for delivery. For QoS 1 it is called when PUBACK is received and for QoS 2 when PUBCOMP is received. The token will be the same token as that returned when the message was published.

Parameters:

token - the delivery token associated with the message.