org.eclipse.paho.client.mqttv3

Interface IMqttAsyncClient

All Known Implementing Classes:

MqttAsyncClient

public interface IMqttAsyncClient

Enables an application to communicate with an MQTT server using non-blocking methods.

It provides applications a simple programming interface to all features of the MQTT version 3.1 specification including:

• connect
• publish
• subscribe
• unsubscribe
• disconnect

There are two styles of MQTT client, this one and IMqttClient.

• IMqttAsyncClient provides a set of non-blocking methods that return control to the invoking application after initial validation of parameters and state. The main processing is performed in the background so as not to block the application program's thread. This non- blocking approach is handy when the application needs to carry on processing while the MQTT action takes place. For instance connecting to an MQTT server can take time, using the non-blocking connect method allows an application to display a busy indicator while the connect action takes place in the background. Non blocking methods are particularly useful in event oriented programs and graphical programs where invoking methods that take time to complete on the the main or GUI thread can cause problems. The non-blocking interface can also be used in blocking form.
• IMqttClient provides a set of methods that block and return control to the application program once the MQTT action has completed. It is a thin layer that sits on top of the IMqttAsyncClient implementation and is provided mainly for compatibility with earlier versions of the MQTT client. In most circumstances it is recommended to use IMqttAsyncClient based clients which allow an application to mix both non-blocking and blocking calls.

An application is not restricted to using one style if an IMqttAsyncClient based client is used as both blocking and non-blocking methods can be used in the same application. If an IMqttClient based client is used then only blocking methods are available to the application. For more details on the blocking client see IMqttClient

There are two forms of non-blocking method:

1.      IMqttToken token = asyncClient.method(parms)
        

   In this form the method returns a token that can be used to track the progress of the action (method). The method provides a waitForCompletion() method that once invoked will block until the action completes. Once completed there are method on the token that can be used to check if the action completed successfully or not. For example to wait until a connect completes:

         IMqttToken conToken;
           conToken = asyncClient.client.connect(conToken);
        ... do some work...
           conToken.waitForCompletion();
        

   To turn a method into a blocking invocation the following form can be used:

        IMqttToken token;
        token = asyncClient.method(parms).waitForCompletion();
        

2.      IMqttToken token method(parms, Object userContext, IMqttActionListener callback)
        

   In this form a callback is registered with the method. The callback will be notified when the action succeeds or fails. The callback is invoked on the thread managed by the MQTT client so it is important that processing is minimised in the callback. If not the operation of the MQTT client will be inhibited. For example to be notified (called back) when a connect completes:

           IMqttToken conToken;
               conToken = asyncClient.connect("some context",new new MqttAsyncActionListener() {
                           public void onSuccess(IMqttToken asyncActionToken) {
                                   log("Connected");
                           }
   
                           public void onFailure(IMqttToken asyncActionToken, Throwable exception) {
                                   log ("connect failed" +exception);
                           }
                     });
         

   An optional context object can be passed into the method which will then be made available in the callback. The context is stored by the MQTT client) in the token which is then returned to the invoker. The token is provided to the callback methods where the context can then be accessed.

To understand when the delivery of a message is complete either of the two methods above can be used to either wait on or be notified when the publish completes. An alternative is to use the MqttCallback.deliveryComplete(IMqttDeliveryToken) method which will also be notified when a message has been delivered to the requested quality of service.

Method Summary

Modifier and Type	Method and Description
void	close() Close the client Releases all resource associated with the client.
IMqttToken	connect() Connects to an MQTT server using the default options.
IMqttToken	connect(MqttConnectOptions options) Connects to an MQTT server using the provided connect options.
IMqttToken	connect(MqttConnectOptions options, java.lang.Object userContext, IMqttActionListener callback) Connects to an MQTT server using the specified options.
IMqttToken	connect(java.lang.Object userContext, IMqttActionListener callback) Connects to an MQTT server using the default options.
IMqttToken	disconnect() Disconnects from the server.
IMqttToken	disconnect(long quiesceTimeout) Disconnects from the server.
IMqttToken	disconnect(long quiesceTimeout, java.lang.Object userContext, IMqttActionListener callback) Disconnects from the server.
IMqttToken	disconnect(java.lang.Object userContext, IMqttActionListener callback) Disconnects from the server.
void	disconnectForcibly() Disconnects from the server forcibly to reset all the states.
void	disconnectForcibly(long disconnectTimeout) Disconnects from the server forcibly to reset all the states.
void	disconnectForcibly(long quiesceTimeout, long disconnectTimeout) Disconnects from the server forcibly to reset all the states.
java.lang.String	getClientId() Returns the client ID used by this client.
IMqttDeliveryToken[]	getPendingDeliveryTokens() Returns the delivery tokens for any outstanding publish operations.
java.lang.String	getServerURI() Returns the address of the server used by this client.
boolean	isConnected() Determines if this client is currently connected to the server.
void	messageArrivedComplete(int messageId, int qos) Indicate that the application has completed processing the message with id messageId.
IMqttDeliveryToken	publish(java.lang.String topic, byte[] payload, int qos, boolean retained) Publishes a message to a topic on the server.
IMqttDeliveryToken	publish(java.lang.String topic, byte[] payload, int qos, boolean retained, java.lang.Object userContext, IMqttActionListener callback) Publishes a message to a topic on the server.
IMqttDeliveryToken	publish(java.lang.String topic, MqttMessage message) Publishes a message to a topic on the server.
IMqttDeliveryToken	publish(java.lang.String topic, MqttMessage message, java.lang.Object userContext, IMqttActionListener callback) Publishes a message to a topic on the server.
void	setCallback(MqttCallback callback) Sets a callback listener to use for events that happen asynchronously.
void	setManualAcks(boolean manualAcks) If manualAcks is set to true, then on completion of the messageArrived callback the MQTT acknowledgements are not sent.
IMqttToken	subscribe(java.lang.String[] topicFilters, int[] qos) Subscribe to multiple topics, each of which may include wildcards.
IMqttToken	subscribe(java.lang.String[] topicFilters, int[] qos, IMqttMessageListener[] messageListeners) Subscribe to multiple topics, each of which may include wildcards.
IMqttToken	subscribe(java.lang.String[] topicFilters, int[] qos, java.lang.Object userContext, IMqttActionListener callback) Subscribes to multiple topics, each of which may include wildcards.
IMqttToken	subscribe(java.lang.String[] topicFilters, int[] qos, java.lang.Object userContext, IMqttActionListener callback, IMqttMessageListener[] messageListeners) Subscribe to multiple topics, each of which may include wildcards.
IMqttToken	subscribe(java.lang.String topicFilter, int qos) Subscribe to a topic, which may include wildcards.
IMqttToken	subscribe(java.lang.String topicFilter, int qos, IMqttMessageListener messageListener) Subscribe to a topic, which may include wildcards.
IMqttToken	subscribe(java.lang.String topicFilter, int qos, java.lang.Object userContext, IMqttActionListener callback) Subscribe to a topic, which may include wildcards.
IMqttToken	subscribe(java.lang.String topicFilter, int qos, java.lang.Object userContext, IMqttActionListener callback, IMqttMessageListener messageListener) Subscribe to a topic, which may include wildcards.
IMqttToken	unsubscribe(java.lang.String topicFilter) Requests the server unsubscribe the client from a topic.
IMqttToken	unsubscribe(java.lang.String[] topicFilters) Requests the server unsubscribe the client from one or more topics.
IMqttToken	unsubscribe(java.lang.String[] topicFilters, java.lang.Object userContext, IMqttActionListener callback) Requests the server unsubscribe the client from one or more topics.
IMqttToken	unsubscribe(java.lang.String topicFilter, java.lang.Object userContext, IMqttActionListener callback) Requests the server unsubscribe the client from a topics.

Method Detail

connect

IMqttToken connect()
            throws MqttException,
                   MqttSecurityException

Connects to an MQTT server using the default options.

The default options are specified in MqttConnectOptions class.

Returns:

token used to track and wait for the connect to complete. The token will be passed to the callback methods if a callback is set.

Throws:

MqttSecurityException - for security related problems

MqttException - for non security related problems

See Also:

connect(MqttConnectOptions, Object, IMqttActionListener)

connect

IMqttToken connect(MqttConnectOptions options)
            throws MqttException,
                   MqttSecurityException

Connects to an MQTT server using the provided connect options.

The connection will be established using the options specified in the MqttConnectOptions parameter.

Parameters:

options - a set of connection parameters that override the defaults.

Returns:

token used to track and wait for the connect to complete. The token will be passed to any callback that has been set.

Throws:

MqttSecurityException - for security related problems

MqttException - for non security related problems

See Also:

connect(MqttConnectOptions, Object, IMqttActionListener)

connect

IMqttToken connect(java.lang.Object userContext,
                   IMqttActionListener callback)
            throws MqttException,
                   MqttSecurityException

Connects to an MQTT server using the default options.

The default options are specified in MqttConnectOptions class.

Parameters:

userContext - optional object used to pass context to the callback. Use null if not required.

callback - optional listener that will be notified when the connect completes. Use null if not required.

Returns:

token used to track and wait for the connect to complete. The token will be passed to any callback that has been set.

Throws:

MqttSecurityException - for security related problems

MqttException - for non security related problems

See Also:

connect(MqttConnectOptions, Object, IMqttActionListener)

connect

IMqttToken connect(MqttConnectOptions options,
                   java.lang.Object userContext,
                   IMqttActionListener callback)
            throws MqttException,
                   MqttSecurityException

Connects to an MQTT server using the specified options.

The server to connect to is specified on the constructor. It is recommended to call setCallback(MqttCallback) prior to connecting in order that messages destined for the client can be accepted as soon as the client is connected.

The method returns control before the connect completes. Completion can be tracked by:

• Waiting on the returned token IMqttToken.waitForCompletion() or
• Passing in a callback IMqttActionListener

Parameters:

options - a set of connection parameters that override the defaults.

userContext - optional object for used to pass context to the callback. Use null if not required.

callback - optional listener that will be notified when the connect completes. Use null if not required.

Returns:

token used to track and wait for the connect to complete. The token will be passed to any callback that has been set.

Throws:

MqttSecurityException - for security related problems

MqttException - for non security related problems including communication errors

disconnect

IMqttToken disconnect()
               throws MqttException

Disconnects from the server.

An attempt is made to quiesce the client allowing outstanding work to complete before disconnecting. It will wait for a maximum of 30 seconds for work to quiesce before disconnecting. This method must not be called from inside MqttCallback methods.

Returns:

token used to track and wait for disconnect to complete. The token will be passed to any callback that has been set.

Throws:

MqttException - for problems encountered while disconnecting

See Also:

disconnect(long, Object, IMqttActionListener)

disconnect

IMqttToken disconnect(long quiesceTimeout)
               throws MqttException

Disconnects from the server.

An attempt is made to quiesce the client allowing outstanding work to complete before disconnecting. It will wait for a maximum of the specified quiesce time for work to complete before disconnecting. This method must not be called from inside MqttCallback methods.

Parameters:

quiesceTimeout - the amount of time in milliseconds to allow for existing work to finish before disconnecting. A value of zero or less means the client will not quiesce.

Returns:

token used to track and wait for disconnect to complete. The token will be passed to the callback methods if a callback is set.

Throws:

MqttException - for problems encountered while disconnecting

See Also:

disconnect(long, Object, IMqttActionListener)

disconnect

IMqttToken disconnect(java.lang.Object userContext,
                      IMqttActionListener callback)
               throws MqttException

Disconnects from the server.

An attempt is made to quiesce the client allowing outstanding work to complete before disconnecting. It will wait for a maximum of 30 seconds for work to quiesce before disconnecting. This method must not be called from inside MqttCallback methods.

Parameters:

userContext - optional object used to pass context to the callback. Use null if not required.

callback - optional listener that will be notified when the disconnect completes. Use null if not required.

Returns:

token used to track and wait for the disconnect to complete. The token will be passed to any callback that has been set.

Throws:

MqttException - for problems encountered while disconnecting

See Also:

disconnect(long, Object, IMqttActionListener)

disconnect

IMqttToken disconnect(long quiesceTimeout,
                      java.lang.Object userContext,
                      IMqttActionListener callback)
               throws MqttException

Disconnects from the server.

The client will wait for MqttCallback methods to complete. It will then wait for up to the quiesce timeout to allow for work which has already been initiated to complete. For instance when a QoS 2 message has started flowing to the server but the QoS 2 flow has not completed.It prevents new messages being accepted and does not send any messages that have been accepted but not yet started delivery across the network to the server. When work has completed or after the quiesce timeout, the client will disconnect from the server. If the cleanSession flag was set to false and is set to false the next time a connection is made QoS 1 and 2 messages that were not previously delivered will be delivered.

This method must not be called from inside MqttCallback methods.

The method returns control before the disconnect completes. Completion can be tracked by:

• Waiting on the returned token IMqttToken.waitForCompletion() or
• Passing in a callback IMqttActionListener

Parameters:

quiesceTimeout - the amount of time in milliseconds to allow for existing work to finish before disconnecting. A value of zero or less means the client will not quiesce.

userContext - optional object used to pass context to the callback. Use null if not required.

callback - optional listener that will be notified when the disconnect completes. Use null if not required.

Returns:

token used to track and wait for the connect to complete. The token will be passed to any callback that has been set.

Throws:

MqttException - for problems encountered while disconnecting

disconnectForcibly

void disconnectForcibly()
                 throws MqttException

Disconnects from the server forcibly to reset all the states. Could be useful when disconnect attempt failed.

Because the client is able to establish the TCP/IP connection to a none MQTT server and it will certainly fail to send the disconnect packet. It will wait for a maximum of 30 seconds for work to quiesce before disconnecting and wait for a maximum of 10 seconds for sending the disconnect packet to server.

Throws:

MqttException - if any unexpected error

Since:

0.4.1

disconnectForcibly

void disconnectForcibly(long disconnectTimeout)
                 throws MqttException

Disconnects from the server forcibly to reset all the states. Could be useful when disconnect attempt failed.

Because the client is able to establish the TCP/IP connection to a none MQTT server and it will certainly fail to send the disconnect packet. It will wait for a maximum of 30 seconds for work to quiesce before disconnecting.

Parameters:

disconnectTimeout - the amount of time in milliseconds to allow send disconnect packet to server.

Throws:

MqttException - if any unexpected error

Since:

0.4.1

disconnectForcibly

void disconnectForcibly(long quiesceTimeout,
                        long disconnectTimeout)
                 throws MqttException

Disconnects from the server forcibly to reset all the states. Could be useful when disconnect attempt failed.

Because the client is able to establish the TCP/IP connection to a none MQTT server and it will certainly fail to send the disconnect packet.

Parameters:

quiesceTimeout - the amount of time in milliseconds to allow for existing work to finish before disconnecting. A value of zero or less means the client will not quiesce.

disconnectTimeout - the amount of time in milliseconds to allow send disconnect packet to server.

Throws:

MqttException - if any unexpected error

Since:

0.4.1

isConnected

boolean isConnected()

Determines if this client is currently connected to the server.

Returns:

true if connected, false otherwise.

getClientId

java.lang.String getClientId()

Returns the client ID used by this client.

All clients connected to the same server or server farm must have a unique ID.

Returns:

the client ID used by this client.

getServerURI

java.lang.String getServerURI()

Returns the address of the server used by this client.

The format of the returned String is the same as that used on the constructor.

Returns:

the server's address, as a URI String.

See Also:

MqttAsyncClient.MqttAsyncClient(String, String)

publish

IMqttDeliveryToken publish(java.lang.String topic,
                           byte[] payload,
                           int qos,
                           boolean retained)
                    throws MqttException,
                           MqttPersistenceException

Publishes a message to a topic on the server.

A convenience method, which will create a new MqttMessage object with a byte array payload and the specified QoS, and then publish it.

Parameters:

topic - to deliver the message to, for example "finance/stock/ibm".

payload - the byte array to use as the payload

qos - the Quality of Service to deliver the message at. Valid values are 0, 1 or 2.

retained - whether or not this message should be retained by the server.

Returns:

token used to track and wait for the publish to complete. The token will be passed to any callback that has been set.

Throws:

MqttPersistenceException - when a problem occurs storing the message

java.lang.IllegalArgumentException - if value of QoS is not 0, 1 or 2.

MqttException - for other errors encountered while publishing the message. For instance if too many messages are being processed.

See Also:

publish(String, MqttMessage, Object, IMqttActionListener), MqttMessage.setQos(int), MqttMessage.setRetained(boolean)

publish

IMqttDeliveryToken publish(java.lang.String topic,
                           byte[] payload,
                           int qos,
                           boolean retained,
                           java.lang.Object userContext,
                           IMqttActionListener callback)
                    throws MqttException,
                           MqttPersistenceException

Publishes a message to a topic on the server.

A convenience method, which will create a new MqttMessage object with a byte array payload and the specified QoS, and then publish it.

Parameters:

topic - to deliver the message to, for example "finance/stock/ibm".

payload - the byte array to use as the payload

qos - the Quality of Service to deliver the message at. Valid values are 0, 1 or 2.

retained - whether or not this message should be retained by the server.

userContext - optional object used to pass context to the callback. Use null if not required.

callback - optional listener that will be notified when message delivery hsa completed to the requested quality of service

Returns:

token used to track and wait for the publish to complete. The token will be passed to any callback that has been set.

Throws:

MqttPersistenceException - when a problem occurs storing the message

java.lang.IllegalArgumentException - if value of QoS is not 0, 1 or 2.

MqttException - for other errors encountered while publishing the message. For instance client not connected.

See Also:

publish(String, MqttMessage, Object, IMqttActionListener), MqttMessage.setQos(int), MqttMessage.setRetained(boolean)

publish

IMqttDeliveryToken publish(java.lang.String topic,
                           MqttMessage message)
                    throws MqttException,
                           MqttPersistenceException

Publishes a message to a topic on the server. Takes an MqttMessage message and delivers it to the server at the requested quality of service.

Parameters:

topic - to deliver the message to, for example "finance/stock/ibm".

message - to deliver to the server

Returns:

token used to track and wait for the publish to complete. The token will be passed to any callback that has been set.

Throws:

MqttPersistenceException - when a problem occurs storing the message

java.lang.IllegalArgumentException - if value of QoS is not 0, 1 or 2.

MqttException - for other errors encountered while publishing the message. For instance client not connected.

See Also:

publish(String, MqttMessage, Object, IMqttActionListener)

publish

IMqttDeliveryToken publish(java.lang.String topic,
                           MqttMessage message,
                           java.lang.Object userContext,
                           IMqttActionListener callback)
                    throws MqttException,
                           MqttPersistenceException

Publishes a message to a topic on the server.

Once this method has returned cleanly, the message has been accepted for publication by the client and will be delivered on a background thread. In the event the connection fails or the client stops. Messages will be delivered to the requested quality of service once the connection is re-established to the server on condition that:

• The connection is re-established with the same clientID
• The original connection was made with (@link MqttConnectOptions#setCleanSession(boolean)} set to false
• The connection is re-established with (@link MqttConnectOptions#setCleanSession(boolean)} set to false
• Depending when the failure occurs QoS 0 messages may not be delivered.

When building an application, the design of the topic tree should take into account the following principles of topic name syntax and semantics:

• A topic must be at least one character long.
• Topic names are case sensitive. For example, ACCOUNTS and Accounts are two different topics.
• Topic names can include the space character. For example, Accounts payable is a valid topic.
• A leading "/" creates a distinct topic. For example, /finance is different from finance. /finance matches "+/+" and "/+", but not "+".
• Do not include the null character (Unicode \x0000) in any topic.

The following principles apply to the construction and content of a topic tree:

• The length is limited to 64k but within that there are no limits to the number of levels in a topic tree.
• There can be any number of root nodes; that is, there can be any number of topic trees.

The method returns control before the publish completes. Completion can be tracked by:

• Setting an setCallback(MqttCallback) where the MqttCallback.deliveryComplete(IMqttDeliveryToken) method will be called.
• Waiting on the returned token MqttToken.waitForCompletion() or
• Passing in a callback IMqttActionListener to this method

Parameters:

topic - to deliver the message to, for example "finance/stock/ibm".

message - to deliver to the server

userContext - optional object used to pass context to the callback. Use null if not required.

callback - optional listener that will be notified when message delivery has completed to the requested quality of service

Returns:

token used to track and wait for the publish to complete. The token will be passed to callback methods if set.

Throws:

MqttPersistenceException - when a problem occurs storing the message

java.lang.IllegalArgumentException - if value of QoS is not 0, 1 or 2.

MqttException - for other errors encountered while publishing the message. For instance client not connected.

See Also:

MqttMessage

subscribe

IMqttToken subscribe(java.lang.String topicFilter,
                     int qos)
              throws MqttException

Subscribe to a topic, which may include wildcards.

Parameters:

topicFilter - the topic to subscribe to, which can include wildcards.

qos - the maximum quality of service at which to subscribe. Messages published at a lower quality of service will be received at the published QoS. Messages published at a higher quality of service will be received using the QoS specified on the subscribe.

Returns:

token used to track and wait for the subscribe to complete. The token will be passed to callback methods if set.

Throws:

MqttException - if there was an error registering the subscription.

See Also:

subscribe(String[], int[], Object, IMqttActionListener)

subscribe

IMqttToken subscribe(java.lang.String topicFilter,
                     int qos,
                     java.lang.Object userContext,
                     IMqttActionListener callback)
              throws MqttException

Subscribe to a topic, which may include wildcards.

Parameters:

topicFilter - the topic to subscribe to, which can include wildcards.

qos - the maximum quality of service at which to subscribe. Messages published at a lower quality of service will be received at the published QoS. Messages published at a higher quality of service will be received using the QoS specified on the subscribe.

userContext - optional object used to pass context to the callback. Use null if not required.

callback - optional listener that will be notified when subscribe has completed

Returns:

token used to track and wait for the subscribe to complete. The token will be passed to callback methods if set.

Throws:

MqttException - if there was an error registering the subscription.

See Also:

subscribe(String[], int[], Object, IMqttActionListener)

subscribe

IMqttToken subscribe(java.lang.String[] topicFilters,
                     int[] qos)
              throws MqttException

Subscribe to multiple topics, each of which may include wildcards.

Provides an optimized way to subscribe to multiple topics compared to subscribing to each one individually.

Parameters:

topicFilters - one or more topics to subscribe to, which can include wildcards

qos - the maximum quality of service at which to subscribe. Messages published at a lower quality of service will be received at the published QoS. Messages published at a higher quality of service will be received using the QoS specified on the subscribe.

Returns:

token used to track and wait for the subscribe to complete. The token will be passed to callback methods if set.

Throws:

MqttException - if there was an error registering the subscription.

See Also:

subscribe(String[], int[], Object, IMqttActionListener)

subscribe

IMqttToken subscribe(java.lang.String[] topicFilters,
                     int[] qos,
                     java.lang.Object userContext,
                     IMqttActionListener callback)
              throws MqttException

Subscribes to multiple topics, each of which may include wildcards.

Provides an optimized way to subscribe to multiple topics compared to subscribing to each one individually.

The setCallback(MqttCallback) method should be called before this method, otherwise any received messages will be discarded.

If (@link MqttConnectOptions#setCleanSession(boolean)} was set to true when when connecting to the server then the subscription remains in place until either:

• The client disconnects
• An unsubscribe method is called to un-subscribe the topic

If (@link MqttConnectOptions#setCleanSession(boolean)} was set to false when connecting to the server then the subscription remains in place until either:

• An unsubscribe method is called to unsubscribe the topic
• The next time the client connects with cleanSession set to true
With cleanSession set to false the MQTT server will store messages on behalf of the client when the client is not connected. The next time the client connects with the same client ID the server will deliver the stored messages to the client.

The "topic filter" string used when subscribing may contain special characters, which allow you to subscribe to multiple topics at once.

The topic level separator is used to introduce structure into the topic, and can therefore be specified within the topic for that purpose. The multi-level wildcard and single-level wildcard can be used for subscriptions, but they cannot be used within a topic by the publisher of a message.

Topic level separator

The forward slash (/) is used to separate each level within a topic tree and provide a hierarchical structure to the topic space. The use of the topic level separator is significant when the two wildcard characters are encountered in topics specified by subscribers.

Multi-level wildcard

The number sign (#) is a wildcard character that matches any number of levels within a topic. For example, if you subscribe to finance/stock/ibm/#, you receive messages on these topics:

   finance/stock/ibm
   finance/stock/ibm/closingprice
   finance/stock/ibm/currentprice

The multi-level wildcard can represent zero or more levels. Therefore, finance/# can also match the singular finance, where # represents zero levels. The topic level separator is meaningless in this context, because there are no levels to separate.

The multi-level wildcard can be specified only on its own or next to the topic level separator character. Therefore, # and finance/# are both valid, but finance# is not valid. The multi-level wildcard must be the last character used within the topic tree. For example, finance/# is valid but finance/#/closingprice is not valid.

Single-level wildcard

The plus sign (+) is a wildcard character that matches only one topic level. For example, finance/stock/+ matches finance/stock/ibm and finance/stock/xyz, but not finance/stock/ibm/closingprice. Also, because the single-level wildcard matches only a single level, finance/+ does not match finance.

Use the single-level wildcard at any level in the topic tree, and in conjunction with the multilevel wildcard. Specify the single-level wildcard next to the topic level separator, except when it is specified on its own. Therefore, + and finance/+ are both valid, but finance+ is not valid. The single-level wildcard can be used at the end of the topic tree or within the topic tree. For example, finance/+ and finance/+/ibm are both valid.

The method returns control before the subscribe completes. Completion can be tracked by:

• Waiting on the supplied token MqttToken.waitForCompletion() or
• Passing in a callback IMqttActionListener to this method

Parameters:

topicFilters - one or more topics to subscribe to, which can include wildcards

qos - the maximum quality of service to subscribe each topic at.Messages published at a lower quality of service will be received at the published QoS. Messages published at a higher quality of service will be received using the QoS specified on the subscribe.

userContext - optional object used to pass context to the callback. Use null if not required.

callback - optional listener that will be notified when subscribe has completed

Returns:

token used to track and wait for the subscribe to complete. The token will be passed to callback methods if set.

Throws:

MqttException - if there was an error registering the subscription.

java.lang.IllegalArgumentException - if the two supplied arrays are not the same size.

subscribe

IMqttToken subscribe(java.lang.String topicFilter,
                     int qos,
                     java.lang.Object userContext,
                     IMqttActionListener callback,
                     IMqttMessageListener messageListener)
              throws MqttException

Subscribe to a topic, which may include wildcards.

Parameters:

topicFilter - the topic to subscribe to, which can include wildcards.

qos - the maximum quality of service at which to subscribe. Messages published at a lower quality of service will be received at the published QoS. Messages published at a higher quality of service will be received using the QoS specified on the subscribe.

userContext - optional object used to pass context to the callback. Use null if not required.

callback - optional listener that will be notified when subscribe has completed

messageListener - a callback to handle incoming messages

Returns:

token used to track and wait for the subscribe to complete. The token will be passed to callback methods if set.

Throws:

MqttException - if there was an error registering the subscription.

See Also:

subscribe(String[], int[], Object, IMqttActionListener)

subscribe

IMqttToken subscribe(java.lang.String topicFilter,
                     int qos,
                     IMqttMessageListener messageListener)
              throws MqttException

Subscribe to a topic, which may include wildcards.

Parameters:

topicFilter - the topic to subscribe to, which can include wildcards.

qos - the maximum quality of service at which to subscribe. Messages published at a lower quality of service will be received at the published QoS. Messages published at a higher quality of service will be received using the QoS specified on the subscribe.

messageListener - a callback to handle incoming messages

Returns:

token used to track and wait for the subscribe to complete. The token will be passed to callback methods if set.

Throws:

MqttException - if there was an error registering the subscription.

See Also:

subscribe(String[], int[], Object, IMqttActionListener)

subscribe

IMqttToken subscribe(java.lang.String[] topicFilters,
                     int[] qos,
                     IMqttMessageListener[] messageListeners)
              throws MqttException

Subscribe to multiple topics, each of which may include wildcards.

Provides an optimized way to subscribe to multiple topics compared to subscribing to each one individually.

Parameters:

topicFilters - one or more topics to subscribe to, which can include wildcards

qos - the maximum quality of service at which to subscribe. Messages published at a lower quality of service will be received at the published QoS. Messages published at a higher quality of service will be received using the QoS specified on the subscribe.

messageListeners - one or more callbacks to handle incoming messages

Returns:

token used to track and wait for the subscribe to complete. The token will be passed to callback methods if set.

Throws:

MqttException - if there was an error registering the subscription.

See Also:

subscribe(String[], int[], Object, IMqttActionListener)

subscribe

IMqttToken subscribe(java.lang.String[] topicFilters,
                     int[] qos,
                     java.lang.Object userContext,
                     IMqttActionListener callback,
                     IMqttMessageListener[] messageListeners)
              throws MqttException

Subscribe to multiple topics, each of which may include wildcards.

Provides an optimized way to subscribe to multiple topics compared to subscribing to each one individually.

Parameters:

topicFilters - one or more topics to subscribe to, which can include wildcards

qos - the maximum quality of service at which to subscribe. Messages published at a lower quality of service will be received at the published QoS. Messages published at a higher quality of service will be received using the QoS specified on the subscribe.

userContext - optional object used to pass context to the callback. Use null if not required.

callback - optional listener that will be notified when subscribe has completed

messageListeners - one or more callbacks to handle incoming messages

Returns:

token used to track and wait for the subscribe to complete. The token will be passed to callback methods if set.

Throws:

MqttException - if there was an error registering the subscription.

See Also:

subscribe(String[], int[], Object, IMqttActionListener)

unsubscribe

IMqttToken unsubscribe(java.lang.String topicFilter)
                throws MqttException

Requests the server unsubscribe the client from a topic.

Parameters:

topicFilter - the topic to unsubscribe from. It must match a topicFilter specified on an earlier subscribe.

Returns:

token used to track and wait for the unsubscribe to complete. The token will be passed to callback methods if set.

Throws:

MqttException - if there was an error unregistering the subscription.

See Also:

unsubscribe(String[], Object, IMqttActionListener)

unsubscribe

IMqttToken unsubscribe(java.lang.String[] topicFilters)
                throws MqttException

Requests the server unsubscribe the client from one or more topics.

Parameters:

topicFilters - one or more topics to unsubscribe from. Each topicFilter must match one specified on an earlier subscribe. *

Returns:

token used to track and wait for the unsubscribe to complete. The token will be passed to callback methods if set.

Throws:

MqttException - if there was an error unregistering the subscription.

See Also:

unsubscribe(String[], Object, IMqttActionListener)

unsubscribe

IMqttToken unsubscribe(java.lang.String topicFilter,
                       java.lang.Object userContext,
                       IMqttActionListener callback)
                throws MqttException

Requests the server unsubscribe the client from a topics.

Parameters:

topicFilter - the topic to unsubscribe from. It must match a topicFilter specified on an earlier subscribe.

userContext - optional object used to pass context to the callback. Use null if not required.

callback - optional listener that will be notified when unsubscribe has completed

Returns:

token used to track and wait for the unsubscribe to complete. The token will be passed to callback methods if set.

Throws:

MqttException - if there was an error unregistering the subscription.

See Also:

unsubscribe(String[], Object, IMqttActionListener)

unsubscribe

IMqttToken unsubscribe(java.lang.String[] topicFilters,
                       java.lang.Object userContext,
                       IMqttActionListener callback)
                throws MqttException

Requests the server unsubscribe the client from one or more topics.

Unsubcribing is the opposite of subscribing. When the server receives the unsubscribe request it looks to see if it can find a matching subscription for the client and then removes it. After this point the server will send no more messages to the client for this subscription.

The topic(s) specified on the unsubscribe must match the topic(s) specified in the original subscribe request for the unsubscribe to succeed

The method returns control before the unsubscribe completes. Completion can be tracked by:

• Waiting on the returned token MqttToken.waitForCompletion() or
• Passing in a callback IMqttActionListener to this method

Parameters:

topicFilters - one or more topics to unsubscribe from. Each topicFilter must match one specified on an earlier subscribe.

userContext - optional object used to pass context to the callback. Use null if not required.

callback - optional listener that will be notified when unsubscribe has completed

Returns:

token used to track and wait for the unsubscribe to complete. The token will be passed to callback methods if set.

Throws:

MqttException - if there was an error unregistering the subscription.

setCallback

void setCallback(MqttCallback callback)

Sets a callback listener to use for events that happen asynchronously.

There are a number of events that the listener will be notified about. These include:

• A new message has arrived and is ready to be processed
• The connection to the server has been lost
• Delivery of a message to the server has completed

Other events that track the progress of an individual operation such as connect and subscribe can be tracked using the MqttToken returned from each non-blocking method or using setting a IMqttActionListener on the non-blocking method.

Parameters:

callback - which will be invoked for certain asynchronous events

See Also:

MqttCallback

getPendingDeliveryTokens

IMqttDeliveryToken[] getPendingDeliveryTokens()

Returns the delivery tokens for any outstanding publish operations.

If a client has been restarted and there are messages that were in the process of being delivered when the client stopped this method returns a token for each in-flight message enabling the delivery to be tracked Alternately the MqttCallback.deliveryComplete(IMqttDeliveryToken) callback can be used to track the delivery of outstanding messages.

If a client connects with cleanSession true then there will be no delivery tokens as the cleanSession option deletes all earlier state. For state to be remembered the client must connect with cleanSession set to false

Returns:

zero or more delivery tokens

setManualAcks

void setManualAcks(boolean manualAcks)

If manualAcks is set to true, then on completion of the messageArrived callback the MQTT acknowledgements are not sent. You must call messageArrivedComplete to send those acknowledgements. This allows finer control over when the acks are sent. The default behaviour, when manualAcks is false, is to send the MQTT acknowledgements automatically at the successful completion of the messageArrived callback method.

Parameters:

manualAcks -

messageArrivedComplete

void messageArrivedComplete(int messageId,
                            int qos)
                     throws MqttException

Indicate that the application has completed processing the message with id messageId. This will cause the MQTT acknowledgement to be sent to the server.

Parameters:

messageId - the MQTT message id to be acknowledged

qos - the MQTT QoS of the message to be acknowledged

Throws:

MqttException

close

void close()
    throws MqttException

Close the client Releases all resource associated with the client. After the client has been closed it cannot be reused. For instance attempts to connect will fail.

Throws:

MqttException - if the client is not disconnected.