org.apache.pulsar.client.api

Interface Reader<T>

All Superinterfaces:

AutoCloseable, Closeable

public interface Reader<T>
extends Closeable

A Reader can be used to scan through all the messages currently available in a topic.

Method Summary

Modifier and Type	Method and Description
CompletableFuture<Void>	closeAsync() Asynchronously close the reader and stop the broker to push more messages
String	getTopic()
boolean	hasMessageAvailable() Check if there is any message available to read from the current position.
CompletableFuture<Boolean>	hasMessageAvailableAsync() Asynchronously check if there is any message available to read from the current position.
boolean	hasReachedEndOfTopic() Return true if the topic was terminated and this reader has reached the end of the topic.
boolean	isConnected()
Message<T>	readNext() Read the next message in the topic.
Message<T>	readNext(int timeout, TimeUnit unit) Read the next message in the topic waiting for a maximum time.
CompletableFuture<Message<T>>	readNextAsync() Read asynchronously the next message in the topic.

Methods inherited from interface java.io.Closeable

close

Method Detail

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.

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 {@link #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