org.eclipse.paho.client.mqttv3

Interface IMqttClient

All Known Implementing Classes:

MqttClient

public interface IMqttClient

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

This interface allows applications to utilize 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 IMqttAsyncClient.

• IMqttClient provides a set of methods that block and return control to the application program once the MQTT action has completed.
• 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 programs thread. This non blocking approach is handy when the application wants 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 is occurring. Non-blocking methods are particularly useful in event-oriented programs and graphical programs where issuing methods that take time to complete on the the main or GUI thread can cause problems.

The non-blocking client can also be used in a blocking form by turning a non-blocking method into a blocking invocation using the following pattern:

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

Using the non-blocking client allows an application to use a mixture of blocking and non-blocking styles. Using the blocking client only allows an application to use one style. The blocking client provides compatibility with earlier versions of the MQTT client.

Method Summary

Modifier and Type	Method and Description
void	close() Close the client Releases all resource associated with the client.
void	connect() Connects to an MQTT server using the default options.
void	connect(MqttConnectOptions options) Connects to an MQTT server using the specified options.
IMqttToken	connectWithResult(MqttConnectOptions options) Connects to an MQTT server using the specified options.
void	disconnect() Disconnects from the server.
void	disconnect(long quiesceTimeout) 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, as a URI.
MqttTopic	getTopic(java.lang.String topic) Get a topic object which can be used to publish messages.
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.
void	publish(java.lang.String topic, byte[] payload, int qos, boolean retained) Publishes a message to a topic on the server and return once it is delivered.
void	publish(java.lang.String topic, MqttMessage message) Publishes a message to a topic on the server.
void	setCallback(MqttCallback callback) Sets the 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.
void	subscribe(java.lang.String topicFilter) Subscribe to a topic, which may include wildcards using a QoS of 1.
void	subscribe(java.lang.String[] topicFilters) Subscribes to a one or more topics, which may include wildcards using a QoS of 1.
void	subscribe(java.lang.String[] topicFilters, IMqttMessageListener[] messageListeners) Subscribes to a one or more topics, which may include wildcards using a QoS of 1.
void	subscribe(java.lang.String[] topicFilters, int[] qos) Subscribes to multiple topics, each of which may include wildcards.
void	subscribe(java.lang.String[] topicFilters, int[] qos, IMqttMessageListener[] messageListeners) Subscribes to multiple topics, each of which may include wildcards.
void	subscribe(java.lang.String topicFilter, IMqttMessageListener messageListener) Subscribe to a topic, which may include wildcards using a QoS of 1.
void	subscribe(java.lang.String topicFilter, int qos) Subscribe to a topic, which may include wildcards.
void	subscribe(java.lang.String topicFilter, int qos, IMqttMessageListener messageListener) Subscribe to a topic, which may include wildcards.
void	unsubscribe(java.lang.String topicFilter) Requests the server unsubscribe the client from a topic.
void	unsubscribe(java.lang.String[] topicFilters) Requests the server unsubscribe the client from one or more topics.

Method Detail

connect

void connect()
      throws MqttSecurityException,
             MqttException

Connects to an MQTT server using the default options.

The default options are specified in MqttConnectOptions class.

Throws:

MqttSecurityException - when the server rejects the connect for security reasons

MqttException - for non security related problems

See Also:

connect(MqttConnectOptions)

connect

void connect(MqttConnectOptions options)
      throws MqttSecurityException,
             MqttException

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.

This is a blocking method that returns once connect completes

Parameters:

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

Throws:

MqttSecurityException - when the server rejects the connect for security reasons

MqttException - for non security related problems including communication errors

connectWithResult

IMqttToken connectWithResult(MqttConnectOptions options)
                      throws MqttSecurityException,
                             MqttException

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.

This is a blocking method that returns once connect completes

Parameters:

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

Returns:

the MqttToken used for the call. Can be used to obtain the session present flag

Throws:

MqttSecurityException - when the server rejects the connect for security reasons

MqttException - for non security related problems including communication errors

disconnect

void 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.

Throws:

MqttException

See Also:

disconnect(long)

disconnect

void disconnect(long quiesceTimeout)
         throws MqttException

Disconnects from the server.

The client will wait for all 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 example, it will wait for the QoS 2 flows from earlier publications to complete. 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 is a blocking method that returns once disconnect completes

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.

Throws:

MqttException - if a problem is 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

subscribe

void subscribe(java.lang.String topicFilter)
        throws MqttException,
               MqttSecurityException

Subscribe to a topic, which may include wildcards using a QoS of 1.

Parameters:

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

Throws:

MqttException - if there was an error registering the subscription.

MqttSecurityException

See Also:

subscribe(String[], int[])

subscribe

void subscribe(java.lang.String[] topicFilters)
        throws MqttException

Subscribes to a one or more topics, which may include wildcards using a QoS of 1.

Parameters:

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

Throws:

MqttException - if there was an error registering the subscription.

See Also:

subscribe(String[], int[])

subscribe

void 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.

Throws:

MqttException - if there was an error registering the subscription.

See Also:

subscribe(String[], int[])

subscribe

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

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

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 when connecting to the server then the subscription remains in place until either:

• An unsubscribe method is called to unsubscribe the topic
• 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.

This is a blocking method that returns once subscribe completes

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.

Throws:

MqttException - if there was an error registering the subscription.

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

subscribe

void subscribe(java.lang.String topicFilter,
               IMqttMessageListener messageListener)
        throws MqttException,
               MqttSecurityException

Subscribe to a topic, which may include wildcards using a QoS of 1.

Parameters:

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

messageListener - a callback to handle incoming messages

Throws:

MqttException - if there was an error registering the subscription.

MqttSecurityException

See Also:

subscribe(String[], int[])

subscribe

void subscribe(java.lang.String[] topicFilters,
               IMqttMessageListener[] messageListeners)
        throws MqttException

Subscribes to a one or more topics, which may include wildcards using a QoS of 1.

Parameters:

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

messageListeners - one or more callbacks to handle incoming messages

Throws:

MqttException - if there was an error registering the subscription.

See Also:

subscribe(String[], int[])

subscribe

void 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

Throws:

MqttException - if there was an error registering the subscription.

See Also:

subscribe(String[], int[])

subscribe

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

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

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 when connecting to the server then the subscription remains in place until either:

• An unsubscribe method is called to unsubscribe the topic
• 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.

This is a blocking method that returns once subscribe completes

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.

messageListeners - one or more callbacks to handle incoming messages

Throws:

MqttException - if there was an error registering the subscription.

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

unsubscribe

void 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 the subscribe.

Throws:

MqttException - if there was an error unregistering the subscription.

See Also:

unsubscribe(String[])

unsubscribe

void unsubscribe(java.lang.String[] topicFilters)
          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 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 subscribe to succeed

This is a blocking method that returns once unsubscribe completes

Parameters:

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

Throws:

MqttException - if there was an error unregistering the subscription.

publish

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

Publishes a message to a topic on the server and return once it is delivered.

This is a convenience method, which will create a new MqttMessage object with a byte array payload and the specified QoS, and then publish it. All other values in the message will be set to the defaults.

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.

Throws:

MqttPersistenceException - when a problem with 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), MqttMessage.setQos(int), MqttMessage.setRetained(boolean)

publish

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

Publishes a message to a topic on the server.

Delivers a message to the server at the requested quality of service and returns control once the message has been delivered. In the event the connection fails or the client stops, any messages that are in the process of being delivered will be delivered once a 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

In the event that the connection breaks or the client stops it is still possible to determine when the delivery of the message completes. Prior to re-establishing the connection to the server:

• Register a setCallback(MqttCallback) callback on the client and the delivery complete callback will be notified once a delivery of a message completes
• or call getPendingDeliveryTokens() which will return a token for each message that is in-flight. The token can be used to wait for delivery to complete.

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.

This is a blocking method that returns once publish completes

*

Parameters:

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

message - to delivery to the server

Throws:

MqttPersistenceException - when a problem with 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.

setCallback

void setCallback(MqttCallback callback)

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

There are a number of events that 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 passed to the operation

Parameters:

callback - the class to callback when for events related to the client

See Also:

MqttCallback

getTopic

MqttTopic getTopic(java.lang.String topic)

Get a topic object which can be used to publish messages.

An alternative method that should be used in preference to this one when publishing a message is:

• MqttClient.publish(String, MqttMessage) to publish a message in a blocking manner
• or use publish methods on the non-blocking client like IMqttAsyncClient.publish(String, MqttMessage, Object, IMqttActionListener)

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.

Parameters:

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

Returns:

an MqttTopic object, which can be used to publish messages to the topic.

Throws:

java.lang.IllegalArgumentException - if the topic contains a '+' or '#' wildcard character.

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, as a URI.

The format is the same as specified on the constructor.

Returns:

the server's address, as a URI String.

See Also:

MqttAsyncClient.MqttAsyncClient(String, String)

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 will return a token for each 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.