org.eclipse.paho.client.mqttv3

Interface IMqttClient

All Superinterfaces:

AutoCloseable

All Known Implementing Classes:

MqttClient

public interface IMqttClient
extends AutoCloseable

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

IMqttClient provides a set of methods that block and return control to the application program once the MQTT action has completed.

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.
void	disconnect() Disconnects from the server.
String	getClientId() Returns the client ID used by this client.
String	getServerURI() Returns the address of the server used by this client, as a URI.
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	subscribe(String topicFilter) Subscribe to a topic, which may include wildcards using a QoS of 1.
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.

Method Detail

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.

Specified by:

close in interface AutoCloseable

Throws:

MqttException - if the client is not disconnected.

connect

void connect()
      throws MqttException

Connects to an MQTT server using the default options.

The default options are specified in MqttConnectOptions class.

Throws:

MqttException - for non security related problems

See Also:

connect(MqttConnectOptions)

connect

void connect(MqttConnectOptions options)
      throws 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:

MqttException - for non security related problems including communication errors

disconnect

void disconnect()
         throws MqttException

Disconnects from the server.

This is a blocking method that returns once disconnect completes

Throws:

MqttException - if a problem is encountered while disconnecting

getClientId

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

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:

MqttClient(String, String)

isConnected

boolean isConnected()

Determines if this client is currently connected to the server.

Returns:

true if connected, false otherwise.

publish

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

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:

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(String topic,
             MqttMessage message)
      throws MqttException

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.

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:

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.

Parameters:

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

See Also:

MqttCallback

subscribe

void subscribe(String topicFilter)
        throws MqttException

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.

subscribe

void subscribe(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.

unsubscribe

void unsubscribe(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.