Package 

Interface IMqttToken

  • 
public interface IMqttToken

    Provides a mechanism for tracking the completion of an asynchronous task.

    When using the asynchronous/non-blocking MQTT programming interface all methods/operations that take any time (and in particular those that involve any network operation) return control to the caller immediately. The operation then proceeds to run in the background so as not to block the invoking thread. An IMqttToken is used to track the state of the operation. An application can use the token to wait for an operation to complete. A token is passed to callbacks once the operation completes and provides context linking it to the original request. A token is associated with a single operation.

    An action is in progress until either:

    • isComplete() returns true or
    • getException() is not null.

    • Method Summary

      Modifier and Type Method Description
      abstract void waitForCompletion() Blocks the current thread until the action this token is associated with has completed.
      abstract void waitForCompletion(long timeout) Blocks the current thread until the action this token is associated with has completed.
      abstract boolean isComplete() Returns whether or not the action has finished.
      abstract MqttException getException() Returns an exception providing more detail if an operation failed.
      abstract void setActionCallback(IMqttActionListener listener) Register a listener to be notified when an action completes.
      abstract IMqttActionListener getActionCallback() Return the async listener for this token.
      abstract IMqttAsyncClient getClient() Returns the MQTT client that is responsible for processing the asynchronous action
      abstract Array<String> getTopics() Returns the topic string(s) for the action being tracked by this token.
      abstract void setUserContext(Object userContext) Store some context associated with an action.
      abstract Object getUserContext() Retrieve the context associated with an action.
      abstract int getMessageId() Returns the message ID of the message that is associated with the token.

      • Methods inherited from class java.lang.Object

        clone, equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait

    • Method Detail

      • waitForCompletion

         abstract void waitForCompletion()

        Blocks the current thread until the action this token is associated with has completed.

      • waitForCompletion

         abstract void waitForCompletion(long timeout)

        Blocks the current thread until the action this token is associated with has completed.

        The timeout specifies the maximum time it will block for. If the action completes before the timeout then control returns immediately, if not it will block until the timeout expires.

        If the action being tracked fails or the timeout expires an exception will be thrown. In the event of a timeout the action may complete after timeout.

        Parameters:
        timeout - the maximum amount of time to wait for, in milliseconds.

      • isComplete

         abstract boolean isComplete()

        Returns whether or not the action has finished.

        True will be returned both in the case where the action finished successfully and in the case where it failed. If the action failed getException will be non null.

      • getException

         abstract MqttException getException()

        Returns an exception providing more detail if an operation failed.

        While an action in in progress and when an action completes successfully null will be returned. Certain errors like timeout or shutting down will not set the exception as the action has not failed or completed at that time

      • setActionCallback

         abstract void setActionCallback(IMqttActionListener listener)

        Register a listener to be notified when an action completes.

        Once a listener is registered it will be invoked when the action the token is associated with either succeeds or fails.

        Parameters:
        listener - to be invoked once the action completes

      • getClient

         abstract IMqttAsyncClient getClient()

        Returns the MQTT client that is responsible for processing the asynchronous action

      • getTopics

         abstract Array<String> getTopics()

        Returns the topic string(s) for the action being tracked by this token. If the action has not been initiated or the action has not topic associated with it such as connect then null will be returned.

      • setUserContext

         abstract void setUserContext(Object userContext)

        Store some context associated with an action.

        Allows the caller of an action to store some context that can be accessed from within the ActionListener associated with the action. This can be useful when the same ActionListener is associated with multiple actions

        Parameters:
        userContext - to associate with an action

      • getUserContext

         abstract Object getUserContext()

        Retrieve the context associated with an action.

        Allows the ActionListener associated with an action to retrieve any context that was associated with the action when the action was invoked. If not context was provided null is returned.

      • getMessageId

         abstract int getMessageId()

        Returns the message ID of the message that is associated with the token. A message id of zero will be returned for tokens associated with connect, disconnect and ping operations as there can only ever be one of these outstanding at a time. For other operations the MQTT message id flowed over the network.