org.eclipse.paho.client.mqttv3
Class MqttClient

java.lang.Object
  extended by org.eclipse.paho.client.mqttv3.MqttClient
All Implemented Interfaces:
IMqttClient

public class MqttClient
extends Object
implements IMqttClient

Lightweight client for talking to an MQTT server using methods that block until an operation completes.

This class implements the blocking IMqttClient client interface where all actions block until they have completed (or timed out). This implementation is compatible with all Java SE runtimes from 1.4.2 and up.

An application can connect to an MQTT server using:

To enable messages to be delivered even across network and client restarts messages need to be safely stored until the message has been delivered at the requested quality of service. A pluggable persistence mechanism is provided to store the messages.

By default MqttDefaultFilePersistence is used to store messages to a file. If persistence is set to null then messages are stored in memory and hence can be lost if the client, Java runtime or device shuts down.

If connecting with MqttConnectOptions.setCleanSession(boolean) set to true it is safe to use memory persistence as all state it cleared when a client disconnects. If connecting with cleanSession set to false, to provide reliable message delivery then a persistent message store should be used such as the default one.

The message store interface is pluggable. Different stores can be used by implementing the MqttClientPersistence interface and passing it to the clients constructor.

See Also:
IMqttClient

Field Summary
protected  MqttAsyncClient aClient
           
 Logger log
           
protected  long timeToWait
           
 
Constructor Summary
MqttClient(String serverURI, String clientId)
          Create an MqttClient that can be used to communicate with an MQTT server.
MqttClient(String serverURI, String clientId, MqttClientPersistence persistence)
          Create an MqttClient that can be used to communicate with an MQTT server.
 
Method Summary
 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.
 void disconnect()
          Disconnects from the server.
 void disconnect(long quiesceTimeout)
          Disconnects from the server.
static String generateClientId()
          Returns a randomly generated client identifier based on the current user's login name and the system time.
 String getClientId()
          Returns the client ID used by this client.
 Debug getDebug()
          Return a debug object that can be used to help solve problems.
 IMqttDeliveryToken[] getPendingDeliveryTokens()
          Returns the delivery tokens for any outstanding publish operations.
 String getServerURI()
          Returns the address of the server used by this client, as a URI.
 long getTimeToWait()
          Return the maximum time to wait for an action to complete.
 MqttTopic getTopic(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 publish(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(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 setTimeToWait(long timeToWaitInMillis)
          Set the maximum time to wait for an action to complete.
 void subscribe(String topicFilter)
          Subscribe to a topic, which may include wildcards using a QoS of 1.
 void subscribe(String[] topicFilters)
          Subscribes to a one or more topics, which may include wildcards using a QoS of 1.
 void subscribe(String[] topicFilters, int[] qos)
          Subscribes to multiple topics, each of which may include wildcards.
 void subscribe(String topicFilter, int qos)
          Subscribe to a topic, which may include wildcards.
 void unsubscribe(String topicFilter)
          Requests the server unsubscribe the client from a topic.
 void unsubscribe(String[] topicFilters)
          Requests the server unsubscribe the client from one or more topics.
 
Methods inherited from class java.lang.Object
clone, equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait
 

Field Detail

aClient

protected MqttAsyncClient aClient

timeToWait

protected long timeToWait

log

public Logger log
Constructor Detail

MqttClient

public MqttClient(String serverURI,
                  String clientId)
           throws MqttException
Create an MqttClient that can be used to communicate with an MQTT server.

The address of a server can be specified on the constructor. Alternatively a list containing one or more servers can be specified using the setServerURIs method on MqttConnectOptions.

The serverURI parameter is typically used with the the clientId parameter to form a key. The key is used to store and reference messages while they are being delivered. Hence the serverURI specified on the constructor must still be specified even if a list of servers is specified on an MqttConnectOptions object. The serverURI on the constructor must remain the same across restarts of the client for delivery of messages to be maintained from a given client to a given server or set of servers.

The address of the server to connect to is specified as a URI. Two types of connection are supported tcp:// for a TCP connection and ssl:// for a TCP connection secured by SSL/TLS. For example:

If the port is not specified, it will default to 1883 for tcp://" URIs, and 8883 for ssl:// URIs.

A client identifier clientId must be specified and be less that 23 characters. It must be unique across all clients connecting to the same server. The clientId is used by the server to store data related to the client, hence it is important that the clientId remain the same when connecting to a server if durable subscriptions or reliable messaging are required.

A convenience method is provided to generate a random client id that should satisfy this criteria - generateClientId(). As the client identifier is used by the server to identify a client when it reconnects, the client must use the same identifier between connections if durable subscriptions or reliable delivery of messages is required.

In Java SE, SSL can be configured in one of several ways, which the client will use in the following order:

In Java ME, the platform settings are used for SSL connections.

An instance of the default persistence mechanism MqttDefaultFilePersistence is used by the client. To specify a different persistence mechanism or to turn off persistence, use the MqttClient(String, String, MqttClientPersistence) constructor.

Parameters:
serverURI - the address of the server to connect to, specified as a URI. Can be overridden using MqttConnectOptions.setServerURIs(String[])
clientId - a client identifier that is unique on the server being connected to
Throws:
IllegalArgumentException - if the URI does not start with "tcp://", "ssl://" or "local://".
IllegalArgumentException - if the clientId is null or is greater than 23 characters in length
MqttException - if any other problem was encountered

MqttClient

public MqttClient(String serverURI,
                  String clientId,
                  MqttClientPersistence persistence)
           throws MqttException
Create an MqttClient that can be used to communicate with an MQTT server.

The address of a server can be specified on the constructor. Alternatively a list containing one or more servers can be specified using the setServerURIs method on MqttConnectOptions.

The serverURI parameter is typically used with the the clientId parameter to form a key. The key is used to store and reference messages while they are being delivered. Hence the serverURI specified on the constructor must still be specified even if a list of servers is specified on an MqttConnectOptions object. The serverURI on the constructor must remain the same across restarts of the client for delivery of messages to be maintained from a given client to a given server or set of servers.

The address of the server to connect to is specified as a URI. Two types of connection are supported tcp:// for a TCP connection and ssl:// for a TCP connection secured by SSL/TLS. For example:

If the port is not specified, it will default to 1883 for tcp://" URIs, and 8883 for ssl:// URIs.

A client identifier clientId must be specified and be less that 23 characters. It must be unique across all clients connecting to the same server. The clientId is used by the server to store data related to the client, hence it is important that the clientId remain the same when connecting to a server if durable subscriptions or reliable messaging are required.

A convenience method is provided to generate a random client id that should satisfy this criteria - generateClientId(). As the client identifier is used by the server to identify a client when it reconnects, the client must use the same identifier between connections if durable subscriptions or reliable delivery of messages is required.

In Java SE, SSL can be configured in one of several ways, which the client will use in the following order:

In Java ME, the platform settings are used for SSL connections.

A persistence mechanism is used to enable reliable messaging. For messages sent at qualities of service (QoS) 1 or 2 to be reliably delivered, messages must be stored (on both the client and server) until the delivery of the message is complete. If messages are not safely stored when being delivered then a failure in the client or server can result in lost messages. A pluggable persistence mechanism is supported via the MqttClientPersistence interface. An implementer of this interface that safely stores messages must be specified in order for delivery of messages to be reliable. In addition MqttConnectOptions.setCleanSession(boolean) must be set to false. In the event that only QoS 0 messages are sent or received or cleanSession is set to true then a safe store is not needed.

An implementation of file-based persistence is provided in class MqttDefaultFilePersistence which will work in all Java SE based systems. If no persistence is needed, the persistence parameter can be explicitly set to null.

Parameters:
serverURI - the address of the server to connect to, specified as a URI. Can be overridden using MqttConnectOptions.setServerURIs(String[])
clientId - a client identifier that is unique on the server being connected to
persistence - the persistence class to use to store in-flight message. If null then the default persistence mechanism is used
Throws:
IllegalArgumentException - if the URI does not start with "tcp://", "ssl://" or "local://"
IllegalArgumentException - if the clientId is null or is greater than 23 characters in length
MqttException - if any other problem was encountered
Method Detail

connect

public void connect()
             throws MqttSecurityException,
                    MqttException
Description copied from interface: IMqttClient
Connects to an MQTT server using the default options.

The default options are specified in MqttConnectOptions class.

Specified by:
connect in interface IMqttClient
Throws:
MqttSecurityException - when the server rejects the connect for security reasons
MqttException - for non security related problems
See Also:
IMqttClient.connect(MqttConnectOptions)

connect

public void connect(MqttConnectOptions options)
             throws MqttSecurityException,
                    MqttException
Description copied from interface: IMqttClient
Connects to an MQTT server using the specified options.

The server to connect to is specified on the constructor. It is recommended to call IMqttClient.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

Specified by:
connect in interface IMqttClient
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

disconnect

public void disconnect()
                throws MqttException
Description copied from interface: IMqttClient
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.

Specified by:
disconnect in interface IMqttClient
Throws:
MqttException
See Also:
IMqttClient.disconnect(long)

disconnect

public void disconnect(long quiesceTimeout)
                throws MqttException
Description copied from interface: IMqttClient
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

Specified by:
disconnect in interface IMqttClient
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

subscribe

public void subscribe(String topicFilter)
               throws MqttException
Description copied from interface: IMqttClient
Subscribe to a topic, which may include wildcards using a QoS of 1.

Specified by:
subscribe in interface IMqttClient
Parameters:
topicFilter - the topic to subscribe to, which can include wildcards.
Throws:
MqttException - if there was an error registering the subscription.
See Also:
IMqttClient.subscribe(String[], int[])

subscribe

public void subscribe(String[] topicFilters)
               throws MqttException
Description copied from interface: IMqttClient
Subscribes to a one or more topics, which may include wildcards using a QoS of 1.

Specified by:
subscribe in interface IMqttClient
Parameters:
topicFilters - the topic to subscribe to, which can include wildcards.
Throws:
MqttException - if there was an error registering the subscription.
See Also:
IMqttClient.subscribe(String[], int[])

subscribe

public void subscribe(String topicFilter,
                      int qos)
               throws MqttException
Description copied from interface: IMqttClient
Subscribe to a topic, which may include wildcards.

Specified by:
subscribe in interface IMqttClient
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:
IMqttClient.subscribe(String[], int[])

subscribe

public void subscribe(String[] topicFilters,
                      int[] qos)
               throws MqttException
Description copied from interface: IMqttClient
Subscribes to multiple topics, each of which may include wildcards.

The IMqttClient.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:


unsubscribe

public void unsubscribe(String topicFilter)
                 throws MqttException
Description copied from interface: IMqttClient
Requests the server unsubscribe the client from a topic.

Specified by:
unsubscribe in interface IMqttClient
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:
IMqttClient.unsubscribe(String[])

unsubscribe

public void unsubscribe(String[] topicFilters)
                 throws MqttException
Description copied from interface: IMqttClient
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

Specified by:
unsubscribe in interface IMqttClient
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

public void publish(String topic,
                    byte[] payload,
                    int qos,
                    boolean retained)
             throws MqttException,
                    MqttPersistenceException
Description copied from interface: IMqttClient
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.

Specified by:
publish in interface IMqttClient
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
MqttException - for other errors encountered while publishing the message. For instance client not connected.
See Also:
IMqttClient.publish(String, MqttMessage), MqttMessage.setQos(int), MqttMessage.setRetained(boolean)

publish

public void publish(String topic,
                    MqttMessage message)
             throws MqttException,
                    MqttPersistenceException
Description copied from interface: IMqttClient
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:

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:

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

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

This is a blocking method that returns once publish completes

*

Specified by:
publish in interface IMqttClient
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
MqttException - for other errors encountered while publishing the message. For instance client not connected.

setTimeToWait

public void setTimeToWait(long timeToWaitInMillis)
                   throws IllegalArgumentException
Set the maximum time to wait for an action to complete.

Set the maximum time to wait for an action to complete before returning control to the invoking application. Control is returned when:


getTimeToWait

public long getTimeToWait()
Return the maximum time to wait for an action to complete.

See Also:
setTimeToWait(long)

close

public void close()
           throws MqttException
Description copied from interface: IMqttClient
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.

Specified by:
close in interface IMqttClient
Throws:
MqttException - if the client is not disconnected.

getClientId

public String getClientId()
Description copied from interface: IMqttClient
Returns the client ID used by this client.

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

Specified by:
getClientId in interface IMqttClient
Returns:
the client ID used by this client.

getPendingDeliveryTokens

public IMqttDeliveryToken[] getPendingDeliveryTokens()
Description copied from interface: IMqttClient
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

Specified by:
getPendingDeliveryTokens in interface IMqttClient
Returns:
zero or more delivery tokens

getServerURI

public String getServerURI()
Description copied from interface: IMqttClient
Returns the address of the server used by this client, as a URI.

The format is the same as specified on the constructor.

Specified by:
getServerURI in interface IMqttClient
Returns:
the server's address, as a URI String.
See Also:
MqttAsyncClient.MqttAsyncClient(String, String)

getTopic

public MqttTopic getTopic(String topic)
Description copied from interface: IMqttClient
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:

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

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

Specified by:
getTopic in interface IMqttClient
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.

isConnected

public boolean isConnected()
Description copied from interface: IMqttClient
Determines if this client is currently connected to the server.

Specified by:
isConnected in interface IMqttClient
Returns:
true if connected, false otherwise.

setCallback

public void setCallback(MqttCallback callback)
Description copied from interface: IMqttClient
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

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

Specified by:
setCallback in interface IMqttClient
Parameters:
callback - the class to callback when for events related to the client
See Also:
MqttCallback

generateClientId

public static String generateClientId()
Returns a randomly generated client identifier based on the current user's login name and the system time.

When cleanSession is set to false, an application must ensure it uses the same client identifier when it reconnects to the server to resume state and maintain assured message delivery.

Returns:
a generated client identifier
See Also:
MqttConnectOptions.setCleanSession(boolean)

getDebug

public Debug getDebug()
Return a debug object that can be used to help solve problems.



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