co.cask.cdap.messaging

Class MessageFetcher

java.lang.Object

co.cask.cdap.messaging.MessageFetcher

public abstract class MessageFetcher
extends Object

A builder to setup parameters for fetching messages from the messaging system. Sub-class needs to override the fetch() method to return a CloseableIterator for fetching messages.

Constructor Summary

Constructors

Constructor and Description
MessageFetcher()

Method Summary

Modifier and Type	Method and Description
abstract co.cask.cdap.api.dataset.lib.CloseableIterator<RawMessage>	fetch() Returns a CloseableIterator that iterates over messages fetched from the messaging system.
protected int	getLimit()
protected byte[]	getStartOffset()
protected Long	getStartTime()
protected org.apache.tephra.Transaction	getTransaction()
protected boolean	isIncludeStart()
MessageFetcher	setLimit(int limit) Sets the maximum limit on number of messages to be fetched.
MessageFetcher	setStartMessage(byte[] startOffset, boolean inclusive) Setup the message fetching starting point based on the given message id.
MessageFetcher	setStartTime(long startTime) Setup the message fetching start time (publish time).
MessageFetcher	setTransaction(org.apache.tephra.Transaction transaction) Sets the transaction to use for fetching.

Methods inherited from class java.lang.Object

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

Constructor Detail

MessageFetcher

public MessageFetcher()

Method Detail

setStartMessage

public MessageFetcher setStartMessage(byte[] startOffset,
                                      boolean inclusive)

Setup the message fetching starting point based on the given message id. Calling this method will clear the start time set by the setStartTime(long) method.

Parameters:

startOffset - the message id to start fetching from.

inclusive - if true, it will include the message identified by the given message id as the first message (if still available in the system); otherwise it won't be included.

Returns:

this instance

setStartTime

public MessageFetcher setStartTime(long startTime)

Setup the message fetching start time (publish time). Calling this method will clear the start offset set by the setStartMessage(byte[], boolean) method.

Parameters:

startTime - timestamp in milliseconds

Returns:

this instance

setTransaction

public MessageFetcher setTransaction(org.apache.tephra.Transaction transaction)

Sets the transaction to use for fetching. It is for transactional consumption.

Parameters:

transaction - the transaction to use for reading messages

Returns:

this instance

setLimit

public MessageFetcher setLimit(int limit)

Sets the maximum limit on number of messages to be fetched. By default, this is set to Integer.MAX_VALUE.

Parameters:

limit - maximum number of messages to be fetched

Returns:

this instance

getStartOffset

@Nullable
protected byte[] getStartOffset()

isIncludeStart

protected boolean isIncludeStart()

getStartTime

@Nullable
protected Long getStartTime()

getTransaction

@Nullable
protected org.apache.tephra.Transaction getTransaction()

getLimit

protected int getLimit()

fetch

public abstract co.cask.cdap.api.dataset.lib.CloseableIterator<RawMessage> fetch()
                                                                          throws co.cask.cdap.api.messaging.TopicNotFoundException,
                                                                                 IOException

Returns a CloseableIterator that iterates over messages fetched from the messaging system.

Throws:

co.cask.cdap.api.messaging.TopicNotFoundException - if the topic does not exist

IOException - if it fails to create the iterator