Package org.apache.pulsar.client.api

Interface Reader<T>

All Superinterfaces:
AutoCloseable, Closeable
@Public @Stable public interface Reader<T> extends Closeable
A Reader can be used to scan through all the messages currently available in a topic.

  • Method Details

    • getTopic

      String getTopic()
      Returns:
      the topic from which this reader is reading from

    • readNext

      Message<T> readNext() throws PulsarClientException
      Read the next message in the topic.

      This method will block until a message is available.

      Returns:
      the next message
      Throws:
      PulsarClientException

    • readNext

      Message<T> readNext(int timeout, TimeUnit unit) throws PulsarClientException
      Read the next message in the topic waiting for a maximum time.

      Returns null if no message is received before the timeout.

      Returns:
      the next message(Could be null if none received in time)
      Throws:
      PulsarClientException

    • readNextAsync

      CompletableFuture<Message<T>> readNextAsync()
      Read asynchronously the next message in the topic.

      readNextAsync() should be called subsequently once returned CompletableFuture gets complete with received message. Else it creates backlog of receive requests in the application.

      The returned future can be cancelled before completion by calling .cancel(false) (CompletableFuture.cancel(boolean)) to remove it from the the backlog of receive requests. Another choice for ensuring a proper clean up of the returned future is to use the CompletableFuture.orTimeout method which is available on JDK9+. That would remove it from the backlog of receive requests if receiving exceeds the timeout.

      Returns:
      a future that will yield a message (when it's available) or PulsarClientException if the reader is already closed.

    • closeAsync

      CompletableFuture<Void> closeAsync()
      Asynchronously close the reader and stop the broker to push more messages.
      Returns:
      a future that can be used to track the completion of the operation

    • hasReachedEndOfTopic

      boolean hasReachedEndOfTopic()
      Return true if the topic was terminated and this reader has reached the end of the topic.

      Note that this only applies to a "terminated" topic (where the topic is "sealed" and no more messages can be published) and not just that the reader is simply caught up with the publishers. Use hasMessageAvailable() to check for for that.

    • hasMessageAvailable

      boolean hasMessageAvailable() throws PulsarClientException
      Check if there is any message available to read from the current position.

      This check can be used by an application to scan through a topic and stop when the reader reaches the current last published message. For example: 

      
 while (reader.hasMessageAvailable()) {
     Message<String> msg = reader.readNext();
     // Do something
 }

 // Done reading

      Note that this call might be blocking (see hasMessageAvailableAsync() for async version) and that even if this call returns true, that will not guarantee that a subsequent call to readNext() will not block.

      Returns:
      true if the are messages available to be read, false otherwise
      Throws:
      PulsarClientException - if there was any error in the operation

    • hasMessageAvailableAsync

      CompletableFuture<Boolean> hasMessageAvailableAsync()
      Asynchronously check if there is any message available to read from the current position.

      This check can be used by an application to scan through a topic and stop when the reader reaches the current last published message.

      Returns:
      a future that will yield true if the are messages available to be read, false otherwise, or a PulsarClientException if there was any error in the operation

    • isConnected

      boolean isConnected()
      Returns:
      Whether the reader is connected to the broker

    • seek

      void seek(MessageId messageId) throws PulsarClientException
      Reset the subscription associated with this reader to a specific message id.

      The message id can either be a specific message or represent the first or last messages in the topic.

      • MessageId.earliest : Reset the reader on the earliest message available in the topic
      • MessageId.latest : Reset the reader on the latest message in the topic

      Note: this operation can only be done on non-partitioned topics. For these, one can rather perform the seek() on the individual partitions.

      Parameters:
      messageId - the message id where to reposition the reader
      Throws:
      PulsarClientException

    • seek

      void seek(long timestamp) throws PulsarClientException
      Reset the subscription associated with this reader to a specific message publish time.

      Note: this operation can only be done on non-partitioned topics. For these, one can rather perform the seek() on the individual partitions.

      Parameters:
      timestamp - the message publish time where to reposition the reader The timestamp format should be Unix time in milliseconds.
      Throws:
      PulsarClientException

    • seek

      void seek(Function<String,Object> function) throws PulsarClientException
      Reset the subscription associated with this consumer to a specific message ID or message publish time.

      The Function input is topic+partition. It returns only timestamp or MessageId.

      The return value is the seek position/timestamp of the current partition. Exception is thrown if other object types are returned.

      If returns null, the current partition will not do any processing. Exception in a partition may affect other partitions.

      Parameters:
      function -
      Throws:
      PulsarClientException

    • seekAsync

      CompletableFuture<Void> seekAsync(Function<String,Object> function)
      Reset the subscription associated with this consumer to a specific message ID or message publish time asynchronously.

      The Function input is topic+partition. It returns only timestamp or MessageId.

      The return value is the seek position/timestamp of the current partition. Exception is thrown if other object types are returned.

      If returns null, the current partition will not do any processing. Exception in a partition may affect other partitions.

      Parameters:
      function -
      Returns:

    • seekAsync

      CompletableFuture<Void> seekAsync(MessageId messageId)
      Reset the subscription associated with this reader to a specific message id.

      The message id can either be a specific message or represent the first or last messages in the topic.

      • MessageId.earliest : Reset the reader on the earliest message available in the topic
      • MessageId.latest : Reset the reader on the latest message in the topic

      Note: this operation can only be done on non-partitioned topics. For these, one can rather perform the seek() on the individual partitions.

      Parameters:
      messageId - the message id where to position the reader
      Returns:
      a future to track the completion of the seek operation

    • seekAsync

      CompletableFuture<Void> seekAsync(long timestamp)
      Reset the subscription associated with this reader to a specific message publish time.

      Note: this operation can only be done on non-partitioned topics. For these, one can rather perform the seek() on the individual partitions.

      Parameters:
      timestamp - the message publish time where to position the reader The timestamp format should be Unix time in milliseconds.
      Returns:
      a future to track the completion of the seek operation

    • getLastMessageIds

      List<TopicMessageId> getLastMessageIds() throws PulsarClientException
      Get all the last message id of the topics the reader subscribed.
      Returns:
      the list of TopicMessageId instances of all the topics that the reader subscribed
      Throws:
      PulsarClientException - if failed to get last message id.

    • getLastMessageIdsAsync

      CompletableFuture<List<TopicMessageId>> getLastMessageIdsAsync()
      The asynchronous version of getLastMessageIds().