org.apache.flink.streaming.connectors.kafka

Class FlinkKafkaConsumer<T>

java.lang.Object

org.apache.flink.api.common.functions.AbstractRichFunction

org.apache.flink.streaming.api.functions.source.RichParallelSourceFunction<T>

org.apache.flink.streaming.connectors.kafka.FlinkKafkaConsumerBase<T>

org.apache.flink.streaming.connectors.kafka.FlinkKafkaConsumer<T>

All Implemented Interfaces:

Serializable, Function, RichFunction, ResultTypeQueryable<T>, CheckpointListener, CheckpointedFunction, ParallelSourceFunction<T>, SourceFunction<T>

Direct Known Subclasses:

FlinkKafkaShuffleConsumer

@PublicEvolving
public class FlinkKafkaConsumer<T>
extends FlinkKafkaConsumerBase<T>

The Flink Kafka Consumer is a streaming data source that pulls a parallel data stream from Apache Kafka. The consumer can run in multiple parallel instances, each of which will pull data from one or more Kafka partitions.

The Flink Kafka Consumer participates in checkpointing and guarantees that no data is lost during a failure, and that the computation processes elements "exactly once". (Note: These guarantees naturally assume that Kafka itself does not loose any data.)

Please note that Flink snapshots the offsets internally as part of its distributed checkpoints. The offsets committed to Kafka are only to bring the outside view of progress in sync with Flink's view of the progress. That way, monitoring and other jobs can get a view of how far the Flink Kafka consumer has consumed a topic.

Please refer to Kafka's documentation for the available configuration properties: http://kafka.apache.org/documentation.html#newconsumerconfigs

See Also:

Serialized Form

Nested Class Summary

Nested classes/interfaces inherited from interface org.apache.flink.streaming.api.functions.source.SourceFunction

SourceFunction.SourceContext<T>

Field Summary

Fields

Modifier and Type	Field and Description
static long	DEFAULT_POLL_TIMEOUT From Kafka's Javadoc: The time, in milliseconds, spent waiting in poll if data is not available.
static String	KEY_POLL_TIMEOUT Configuration key to change the polling timeout.
protected long	pollTimeout From Kafka's Javadoc: The time, in milliseconds, spent waiting in poll if data is not available.
protected Properties	properties User-supplied properties for Kafka.

Fields inherited from class org.apache.flink.streaming.connectors.kafka.FlinkKafkaConsumerBase

deserializer, KEY_DISABLE_METRICS, KEY_PARTITION_DISCOVERY_INTERVAL_MILLIS, LOG, MAX_NUM_PENDING_CHECKPOINTS, PARTITION_DISCOVERY_DISABLED

Constructor Summary

Constructors

Constructor and Description
FlinkKafkaConsumer(List<String> topics, DeserializationSchema<T> deserializer, Properties props) Creates a new Kafka streaming source consumer.
FlinkKafkaConsumer(List<String> topics, KafkaDeserializationSchema<T> deserializer, Properties props) Creates a new Kafka streaming source consumer.
FlinkKafkaConsumer(Pattern subscriptionPattern, DeserializationSchema<T> valueDeserializer, Properties props) Creates a new Kafka streaming source consumer.
FlinkKafkaConsumer(Pattern subscriptionPattern, KafkaDeserializationSchema<T> deserializer, Properties props) Creates a new Kafka streaming source consumer.
FlinkKafkaConsumer(String topic, DeserializationSchema<T> valueDeserializer, Properties props) Creates a new Kafka streaming source consumer.
FlinkKafkaConsumer(String topic, KafkaDeserializationSchema<T> deserializer, Properties props) Creates a new Kafka streaming source consumer.

Method Summary

Modifier and Type	Method and Description
protected AbstractFetcher<T,?>	createFetcher(SourceFunction.SourceContext<T> sourceContext, Map<KafkaTopicPartition,Long> assignedPartitionsWithInitialOffsets, SerializedValue<WatermarkStrategy<T>> watermarkStrategy, StreamingRuntimeContext runtimeContext, OffsetCommitMode offsetCommitMode, MetricGroup consumerMetricGroup, boolean useMetrics) Creates the fetcher that connect to the Kafka brokers, pulls data, deserialized the data, and emits it into the data streams.
protected AbstractPartitionDiscoverer	createPartitionDiscoverer(KafkaTopicsDescriptor topicsDescriptor, int indexOfThisSubtask, int numParallelSubtasks) Creates the partition discoverer that is used to find new partitions for this subtask.
protected Map<KafkaTopicPartition,Long>	fetchOffsetsWithTimestamp(Collection<KafkaTopicPartition> partitions, long timestamp)
protected boolean	getIsAutoCommitEnabled()

Methods inherited from class org.apache.flink.streaming.connectors.kafka.FlinkKafkaConsumerBase

adjustAutoCommitConfig, assignTimestampsAndWatermarks, assignTimestampsAndWatermarks, assignTimestampsAndWatermarks, cancel, close, disableFilterRestoredPartitionsWithSubscribedTopics, getEnableCommitOnCheckpoints, getProducedType, initializeState, notifyCheckpointAborted, notifyCheckpointComplete, open, run, setCommitOffsetsOnCheckpoints, setStartFromEarliest, setStartFromGroupOffsets, setStartFromLatest, setStartFromSpecificOffsets, setStartFromTimestamp, snapshotState

Methods inherited from class org.apache.flink.api.common.functions.AbstractRichFunction

getIterationRuntimeContext, getRuntimeContext, setRuntimeContext

Methods inherited from class java.lang.Object

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

Field Detail

KEY_POLL_TIMEOUT

public static final String KEY_POLL_TIMEOUT

Configuration key to change the polling timeout. *

See Also:

Constant Field Values

DEFAULT_POLL_TIMEOUT

public static final long DEFAULT_POLL_TIMEOUT

From Kafka's Javadoc: The time, in milliseconds, spent waiting in poll if data is not available. If 0, returns immediately with any records that are available now.

See Also:

Constant Field Values

properties

protected final Properties properties

User-supplied properties for Kafka. *

pollTimeout

protected final long pollTimeout

From Kafka's Javadoc: The time, in milliseconds, spent waiting in poll if data is not available. If 0, returns immediately with any records that are available now

Constructor Detail

FlinkKafkaConsumer

public FlinkKafkaConsumer(String topic,
                          DeserializationSchema<T> valueDeserializer,
                          Properties props)

Creates a new Kafka streaming source consumer.

Parameters:

topic - The name of the topic that should be consumed.

valueDeserializer - The de-/serializer used to convert between Kafka's byte messages and Flink's objects.

props -

FlinkKafkaConsumer

public FlinkKafkaConsumer(String topic,
                          KafkaDeserializationSchema<T> deserializer,
                          Properties props)

Creates a new Kafka streaming source consumer.

This constructor allows passing a KafkaDeserializationSchema for reading key/value pairs, offsets, and topic names from Kafka.

Parameters:

topic - The name of the topic that should be consumed.

deserializer - The keyed de-/serializer used to convert between Kafka's byte messages and Flink's objects.

props -

FlinkKafkaConsumer

public FlinkKafkaConsumer(List<String> topics,
                          DeserializationSchema<T> deserializer,
                          Properties props)

Creates a new Kafka streaming source consumer.

This constructor allows passing multiple topics to the consumer.

Parameters:

topics - The Kafka topics to read from.

deserializer - The de-/serializer used to convert between Kafka's byte messages and Flink's objects.

props -

FlinkKafkaConsumer

public FlinkKafkaConsumer(List<String> topics,
                          KafkaDeserializationSchema<T> deserializer,
                          Properties props)

Creates a new Kafka streaming source consumer.

This constructor allows passing multiple topics and a key/value deserialization schema.

Parameters:

topics - The Kafka topics to read from.

deserializer - The keyed de-/serializer used to convert between Kafka's byte messages and Flink's objects.

props -

FlinkKafkaConsumer

public FlinkKafkaConsumer(Pattern subscriptionPattern,
                          DeserializationSchema<T> valueDeserializer,
                          Properties props)

Creates a new Kafka streaming source consumer. Use this constructor to subscribe to multiple topics based on a regular expression pattern.

If partition discovery is enabled (by setting a non-negative value for FlinkKafkaConsumerBase.KEY_PARTITION_DISCOVERY_INTERVAL_MILLIS in the properties), topics with names matching the pattern will also be subscribed to as they are created on the fly.

Parameters:

subscriptionPattern - The regular expression for a pattern of topic names to subscribe to.

valueDeserializer - The de-/serializer used to convert between Kafka's byte messages and Flink's objects.

props -

FlinkKafkaConsumer

public FlinkKafkaConsumer(Pattern subscriptionPattern,
                          KafkaDeserializationSchema<T> deserializer,
                          Properties props)

Creates a new Kafka streaming source consumer. Use this constructor to subscribe to multiple topics based on a regular expression pattern.

If partition discovery is enabled (by setting a non-negative value for FlinkKafkaConsumerBase.KEY_PARTITION_DISCOVERY_INTERVAL_MILLIS in the properties), topics with names matching the pattern will also be subscribed to as they are created on the fly.

This constructor allows passing a KafkaDeserializationSchema for reading key/value pairs, offsets, and topic names from Kafka.

Parameters:

subscriptionPattern - The regular expression for a pattern of topic names to subscribe to.

deserializer - The keyed de-/serializer used to convert between Kafka's byte messages and Flink's objects.

props -

Method Detail

createFetcher

protected AbstractFetcher<T,?> createFetcher(SourceFunction.SourceContext<T> sourceContext,
                                             Map<KafkaTopicPartition,Long> assignedPartitionsWithInitialOffsets,
                                             SerializedValue<WatermarkStrategy<T>> watermarkStrategy,
                                             StreamingRuntimeContext runtimeContext,
                                             OffsetCommitMode offsetCommitMode,
                                             MetricGroup consumerMetricGroup,
                                             boolean useMetrics)
                                      throws Exception

Description copied from class: FlinkKafkaConsumerBase

Creates the fetcher that connect to the Kafka brokers, pulls data, deserialized the data, and emits it into the data streams.

Specified by:

createFetcher in class FlinkKafkaConsumerBase<T>

Parameters:

sourceContext - The source context to emit data to.

assignedPartitionsWithInitialOffsets - The set of partitions that this subtask should handle, with their start offsets.

watermarkStrategy - Optional, a serialized WatermarkStrategy.

runtimeContext - The task's runtime context.

Returns:

The instantiated fetcher

Throws:

Exception - The method should forward exceptions

createPartitionDiscoverer

protected AbstractPartitionDiscoverer createPartitionDiscoverer(KafkaTopicsDescriptor topicsDescriptor,
                                                                int indexOfThisSubtask,
                                                                int numParallelSubtasks)

Description copied from class: FlinkKafkaConsumerBase

Creates the partition discoverer that is used to find new partitions for this subtask.

Specified by:

createPartitionDiscoverer in class FlinkKafkaConsumerBase<T>

Parameters:

topicsDescriptor - Descriptor that describes whether we are discovering partitions for fixed topics or a topic pattern.

indexOfThisSubtask - The index of this consumer subtask.

numParallelSubtasks - The total number of parallel consumer subtasks.

Returns:

The instantiated partition discoverer

fetchOffsetsWithTimestamp

protected Map<KafkaTopicPartition,Long> fetchOffsetsWithTimestamp(Collection<KafkaTopicPartition> partitions,
                                                                  long timestamp)

Specified by:

fetchOffsetsWithTimestamp in class FlinkKafkaConsumerBase<T>

getIsAutoCommitEnabled

protected boolean getIsAutoCommitEnabled()

Specified by:

getIsAutoCommitEnabled in class FlinkKafkaConsumerBase<T>